Removal of theoretical cooling #8 & #6 cylinders mod

[john8662]

I have a small dilemma that I want opinions on, pro and con. First off I have the 97 cooling mods on my 95 K2500 burb. Prior to the install (when I got the burb and didn't know any better) I consulted with a good friend and owner of a local diesel shop about 6.5 cooling. He and I had talked many times about what goes wrong on some of the 6.5's that he had gotten to work on in the shop that had knocks and bad engines. He said that most of them went bad as a result of the #8 cylinder getting too hot and galling. I talked to him many times about what could be done to prevent that from happening. His solution that he had been installing on many early (92-95) 6.5's was a heater hose passage to the passenger side cylinder head. All this consisted of was a piece of 1/2 heater hose, two nipples and a plate for the passenger side head (a plate like whats used on a 6.2 glow controller cigar-style or inhibitor switch). I didn't tow with my 6.5 at the time and didn't really worry about cooling that much so I installed this mod on my 6.5. The plate is installed on the passenger side rear head and gets a nipple installed into it. Then attach the heater hose to the rear of the head and connect it to the extra port on the water pump by installing a nipple in the extra port. It looks like this when installed:

http://members.cox.net/acmdsl/coolingmods/waterdrain/02.jpg

http://members.cox.net/acmdsl/coolingmods/engine3.jpg


The theory behind the mod (whether it works or not) is that it gives the coolant in the hottest point in a GM head a passage directly do the water pump and to a cooler part of the engine or radiator. This mod in theory (without actually looking at where things flow) could allow this area of the head to cool better and better cool the #8 & # 6 cylinders nearest to the hot turbo system. What direction would coolant really flow in this idea?

Later on I got to reading on TDP about 6.5's, I hadn't paid much attention in the past to anything pertaining to 6.5's as I had a 6.2 at the time and never wanted a 6.5 for all the problems I had heard about them. But since I purchased one (I wanted a TURBO DIESEL) I really have enjoyed it and learning about it, I should have gotten one sooner. From my reading on 6.5's I learned that you could upgrade the cooling system to the "97 cooling mods" by replacing the water pump, thermostats, etc (you've all heard it before.) That

[Barry Nave]

This sounds like something for the guys who still run the single stat.
I do wonder though if that hose even flows any water :confused: Looks as though it would be nothing more than a Balance tube.
Knowing the cooling up grade allows more coolent to flow,around the block as not to allow hot spots.I,m thinking only about 9% more flow through rad. is upped yet more flow around block is whats as important.
I'd would pull it out for fear it may cause the up grade to degrade :eek:
Still the ? as you state, How or if there is any flow through that hose and what diweck-son :D
Just went out to look at the water pump. That port would seem to be a return like the other top side from cross over that takes the flow back to the block. So it would seem as though your pulling coolent from that area, 6&8 and taking it back through the block,as is what the cooling up grade is doing. May be now taking to much hot coolent back through the block and not letting it go to the Rad.
Now take this ideal on a single stat,with a high flow thermastat and a high flow pump and you may have something going on.
Can't what to see this thread go :D

[ 02-22-2004, 02:36 AM: Message edited by: Bnave95 ]

[gmctd]

Several types of infra-red laser spot-temperature digital thermometers are available.

I would take measurements back to front on each head, starting at the rear block-off plates, then between the intake ports, then the outlets into the coolant cross-over.

Do this with engine at normal temps, at idle and cruise rpm.
Block off radiator air flow, so temps rise, fan clutch is fully engaged, take the readings again, same spots, same rpms.

Block off the mod hose with vise-grips, take all readings again, same method, same coolant temp ranges.

Removes all guess-work, gives a reliable base of information.

Would get better readings on the exhaust side, but the turbo manifold is a major restriction.

[grape]

I asked over a year ago about running those outlets up to the crossover behind the thermostat. Works on hot rod 700 horse gas engines but was told here it wouldn't work on our complicated 200 horse diesels?????? go figure.

[john8662]

Thanks for the replies, keep em coming.

GMCTD, I like your idea of testing if it really does any good by eliminating it from the system for a little while (penching it off) and seeing temps, and the using it and measuring the temps. If I get something to measure the temps with I'll give it a try. How much do you think a laser temp measuring meter like you were describing would cost me, and where would I get it?

Bnave95, I also wonder if what you were saying is true also, that this flow of water is only throwing hotter coolant from the # 8 & 6 area back into the block. This wouldn't necessarily be a bad thing just that it could effect the effecientcy of the cooling system. This could add hotter coolant to an already warm/hot area into the block to mix with the other yet cooler coolant.

I still have the mod in place, weather it does any good is what I'll need to find out.

Main thing though, is this sort of mod helping or hurting the cooling capacity of the engine, with the 97 HO cooling mods in place?

[Tom C.]

There is a site that sells aftermarket items for Hummers. They have a cool kit for the 6.5 TD that feeds extra coolant to the rear of both heads via the "inspection plates" at the rear of each head. It would be very simple to make for a fraction of what they are selling it for. If you want to take a look email me at me2howu@yahoo.com and I'll send you the link.

Tom C.

[Barry Nave]

Hey Tom, post the link here ;)

[toyboxrv]

If you're expecting that the pump will push more water to the rear of one head, I would doubt it can. The two inlets from the pump to the block are slightly larger than the two outlets going to the thermostat housing. I had installed a temp gauge at the rear of the passenger head and found the temperature to be as much as 20* higher by the #8 cylinder during towing on hills. I bought 2 of the same plates you have and ran hoses from them to the engine side of the thermostat housing. I immediately noticed a significant drop in temps during the same situations. I posted on here about my mods, but was dismissed by most as having created more of a problem than I was solving. Despite everyone else's opinion, I still stick to the effectiveness of this mod.

[Kidd]

I picked up a laser infrared temp meter at my local parts jobber for about 100 bucks. The laser shows exactly where you are reading temps.
K.D.

[mhagie]

To add to the confusion I have a 93 6.2 block bored to 6.5 specs w/Banks Turbo, At rear of right head I installed a temp sender (Nordskog) digital temp gauge from Summit racing.
I just installed it late November and only managed about 50 miles on it before retiring truck for the winter,during the time I run it the digital temp gauge never exceded 170* this is with a 195* stat and factory dash gauge reading a tad shy of 200*.
One of these days I plan to remove sender and heat it in a pan of water to check accuracy cause I can't believe that the back of the cyl head is running cooler than the center where the factory temp sender is located.
To make matters worse the glow plug temp switch is located on rear of left head and it is acting funny also, it is supposed to open at approx 150* so glow plugs will not operate above that temp, but when I drove it last at normal temp on factory gauge the glow plugs still cycle so the temp switch is not breaking contact.
Every sender on the engine is new so now I have to figure out which is the bad one.
The fast idle switch does work droping idle down around 100* recorded on the digital gauge.
I am tempted to dump the digital gauge for a 2 5/8 mechanical gauge cause I believe its accuracy is in question here, I never did like electric gauges, but that green Led does look really cool.
Thoughts?..........Merle

[gmctd]

Thanks, K.D. - I had thought they were still up around 200.

The tap used in the modification is on the intake side of the water pump, so the coolant drawn from the rear of the head would be recirculated along with coolant drawn from the cross-over bypass.

It might require enlarging the coolant passages in the head gaskets to be really effective.
The passages are gaged small at the front, increasing in diameter towards the back to meter block-to-head coolant flow.
This is due to increasing frictional drag as the coolant must flow around the cylinders on it's way thru the block.

A laser spot-check would tell the tale.

p.s.

Merle I'd stick the digital sender in various places in question - rear head, front head, cross-over, etc - to get an accurate reading.
It probably won't be off more than a degree or two, and might set your mind at ease as to what's actually happening.

[ 02-22-2004, 07:09 PM: Message edited by: gmctd ]

[ANXIOUS-SUBMAN]

Please be aware that the lazer pointer on those infrared meters is just that, a pointer. The meter is not just indicating the temp at that small point of light but instead the lazer indicates the center of a much larger area from which the temp is averaged. These are optical divices and so the farther away from an object you are with the meter the larger the area that is averaged. I've watched people in the plant point these things at a steam pipe 20' over their head thinking they are only getting the temp of the pipe cuz they have that little lazer on it when they are actually getting the average temp from about a 10' circle around the pipe. The brochure for the Raytek MiniTemp has a good illustration of how these work. Raytek MiniTemp (http://www.raytek-northamerica.com/admin/file_handler/2ae6092f570efab9e577de9b6820919c/1013708266/MT_Brochure_RevC.pdf)

[john8662]

Tom C.,

Would you post the link to the Hummer cooling upgrade, so that we can all see what you're talking about. I would be interested if it is plumbed similar to what I have installed and what they back their product with. Whether they have any proof that this type of mod does better cool the suspect area of the head.

GMCTD, you bring an interesting point that if the ports in the heads are not very large that the existing cooling system is probably more than sufficient to push enough coolant though the passages anyways. So, in conclusion, that would mean that the mod wouldn't do much good anyways, without the enlargement of the ports in the heads and gaskets.

I'm a little strapped for cash, so I don't think I will be able to get a digital temp meter any time soon, as I would probably put the money in other upgrades. Anyone want to lend me one for testing? Thanks for the replies! Still haven't decided whether to take it off or not.

[Barry Nave]

John
Sounds like it's not doing any harm,maybe some good and may be not. Like to be more work still ahead. Hummer has it so it's been done. More pluming to work around :eek:
The cooling up grade,the updated fan and clutch seem to be the ticket for the 6.5 with added HP.
I'm one that needs my truck to last for ever :D New trucks are out of the price and I know all I have done to my truck to make it live.
Some of my jobs the owner thinks the truck is new and not a 95.
So any ideals I can pick up on I'll use :D

[C.K. Piquup]

I wunder what a little radiator would do for that extra hose(like a section of baseboard).

[grape]

what I'm doing next will blow your minds. I'm mounting the double stat housing on the rear of the engine with the hose outlet pointing forward on the pass side. Using the bypass on the housing to go to the heater core, then connecting the front therm housing holes to the water pump bypass with a t just infront of the injection pump. This ought to be interesting. At least I won't have to butcher the housing for the mechanical injection.

[gmctd]

When I first stumbled across the dual t-stat cross-over in a boneyard, without knowing exactly what it was, that was my first thought - mounted at the rear of the engine, hose outlet facing forward to the radiator.

Motorhome? Stationary? What?

Then I checked the coolant passages thru the decks in a bare 6.5L block, and knew that was not the purpose or correct location.

It was a neat piece, and for only $5, so I bought it anyway.

Fortuitous move!

A short while later, I saw More Power's coolant upgrade article, and there it was.

Long, slow pitch before the fast curve.......

Point being - if you have not, you might compare the deck passages to the restrictions in the gaskets, see what you think about front-to-back flow thru the block, parallel flow block-to-heads, and back-to-front flow thru the heads in oem configuration.

Seems to me, decks and gaskets will require some modification, particularly for the turbocharged engines.

Anyone with further thoughts?

edited for content, to fit time allotted, and for screen width. ;)

[ 02-23-2004, 12:37 PM: Message edited by: gmctd ]

[john8662]

OK, so it looks like no one has really a reason why it shouldn't be on there, that possibly it could give a small margin of added cooling to the hottest part of the engine. For now, I'll leave it until proven otherwise. Only weird thing is if I have to take this rig in eventually for an in warranty pump replacement, the mechanic will have something to poder about, as well as the other upgrades. Anyways, eventually I will need to borrow or eventually purchase a digital laser temp meter for further testing. If I can test it, then maybe I can prove that it does help, even for an already upgraded engine. Thanks for the suggestions and ideas!

[toyboxrv]

It would work better if it took water from both heads. Since both are hotter in the rear, you should be diverting an equal amount of water from each head to balance the flow.Drawing the water into the pump would recirculate it into the engine, whereas putting it into the thermo housing would allow it to go to the radiator to be cooled.

[ucdavis]

Couldn't tell you if its good, bad or indifferent for cooling. But i'd suspect it is hard to purge the air from that tubing sinc it represents sort of a high spot in the assembly; so if you are using DexCool or equivalent "permanent" anti-freeze, the more rapid oxidation from air entrained in the high tech coolant could be an issue. The early radiator/coolant failures on GM v6's, IIRC, were from not getting the air properly bled from the system.
Just my $.02.

[Tom C.]

I don't know if this applies to what you are trying to do but the "cool kit" in the following link bleeds off coolant from a heater hose and routes it to the rear of the heads by way of the "inspection plates". I don't think the idea is to add cooler water to the heads but to increase flow to an area that tends to stagnate. I saw a post by some one who claimed a 10 degree drop in temps in the back of the heads after doing this mod. Its been quite a while back and I have no idea even of what web site I read about it on but I kept the link. It would be very simple to construct your own very cheaply.

http://www.humhers.com/

Tom C.

[john8662]

Tom C.,

Thanks for posting the link to the Hummer cooling upgrade kit! I can't tell from just looking at it where it hooks up though from the description on the page. It either connects on the thermostat housing or in the suction port on the waterpump as I have used.

From what I understand from our discussion, the upgrade isn't a bad idea, and I think the most positive thing that would come of it is that it would get better flow to the hottest part of the engine. Not necessarily cooler coolant. Maybee a change in tube size is also in order, smaller, easier to bleed. Some points that are well taken:

The tube would be hard to bleed all the air out, and this IS a problem with Dexcool systems, mine is converted. After the install I bled out all the air I could multiples times to make sure I got it all, after the system had circulated of course.

Another point, why not do both sides? I conclude this with just saying that I think the hottest head is where #6 and #8 are located, typical GM head, whether diesel or gasser. I think that doing just the one would be sufficient, as it's hotter due to where the turbo junctions. This passenger side head gets heat from both sides of the engine. So, the drivers side would be cooler because it could have less backpressure and less built up combined heat.

[whatnot]

Laser thermometers on ebay. (http://search.ebay.com/search/search.dll?query=raytek&ht=1&sosortproperty=1&from=R10&BasicSearch=)

[Barry Nave]

Good price :D Have one on the way.
Thanks for the info ;)

[grape]

That kit appears to have AN 4 lines which are about the size of brake lines. Not to mention it's not even braided......with brass hardware store fittings. That thing could be built for about 30 bucks.

[Tom C.]

John8662,

To install the cool kit you splice into one of the heater lines. The two flat plates replace the ones mounted way at the back of your heads. The needle valve is there to adjust flow and kind of keep things in balance. It just adds a little flow to an area of stagnation.
Tom C.

[gmctd]

Thanks, Whatnot - they've expanded their lines since last I looked.
The 200 buck models were what I was interested in.

And, while Anxious Subman is correct on actual useage, coolant temp readings will be within 6" of the actual target, and should be accurate enough for these purposes.

[JeepSJ]

We did a similar type of bypass on one of our Bonneville cars. The point was to get some extra cooling around the back cylinders and to try to reduce the coolant temps in the heads. The coolant is getting fairly hot by the time it gets back there and we wanted to try to even out the temps between cylinders. On that engine, we tapped into the passages on the back of the intake and ran a couple 1/4" lines up and into the cooling passages on the front of the intake. It worked nicely - it really helped stabilize the temps on the back cylinders, plus that very hot water was not being passed back through the heads.

I think if I were to do this on my 6.5, I would run the lines from the inspection plates into the crossover pipe. That would allow the coolant to recirculate as the engine warmed up, then it would go through the radiator with the rest of the coolant after the thermostat(s) opened. Routing those to the water pump would make the superheated coolant return to the block all the time. Depending on your heater hose routing, splicing that into the heater hose may also recirculate the hot coolant. If your heater hose goes into your water pump it would be a problem, but if your heater hose went into your radiator then that should be OK.

I had completely forgotten about that modification until I read this thread. Since my engine is sitting on a stand right now, I think I'll take a look at it.

[lupey6.5]

i have the 130GPH pump and still running a single tstat. would someone please tell me the advantage of leaving the restrictor plate on the bottom of the tstat. the dual crossover doesn't have one :confused:

[gmctd]

The 6.2, with the bypass but no valve, would cycle between 200 to 180 deg rapidly, as the t-stat opened and closed.

GM increased bypass diameter, added the bypass valve to the t-stat in effort to stabilize coolant temps in the 6.5L.
The PCM versions run best at about 215deg, but adding the turbo increased heat output tremendously.

The t-stat bypass valve was removed for '97, again allowing constant coolant recirculation when t-stats were closed and open.
This prevented some overheating in the #7 and 8 rear cylinders, but the 130gpm water pump was necessary to further increase recirculation.

The dual t-stats allowed faster dumping into the radiator, while continued recirculation stabilized temperatures.

When this system proved itself, power was upped from 195hp to 215hp.

That's my story, and I'm stickin' to it! ;)

You should add the dual t-stat cross-over to complete the coolant system upgrade in your truck.

[JeepSJ]

Anyone have a set of inspection plates that they are willing to part with?

[john8662]

Which inspection plates are you looking for? The ones with the threaded hole in them like I used for my mod, or just the solid block off plates. If you want the plates with the threaded hole in the center, just go to the Stealer and tell em you have an 82 or 83 model 6.2 diesel, and you need the plate for the head that the glow plug controller mounts in.

[tom.mcinerney]

A few months back someone with a Hummer mentioned on a post here that his engine used the blocked-off / inspection cover at the rear of the heads for coolant flow. A few days later i was standing over my engine preparing to install the thermostat crossover after having installed the intake manifold (wrong order of events). It occurred to me that if i put a crossover at both the front and rear of the engine that i'd be in the dual thermo configuration, with better flow/transfer from the rear of the heads. I tried to fit my single-thermo crossover at the rear, but the forward slant interferes with the intake manifold. So i put the single crossover up front, per design. Since i'd been persuaded [by TDP posts] to chop off the factory aluminum tube-end fitting that connects the heater hose to the crossover, i realised that the heater drains hot coolant from the forward psgr head "inspection/crossover" to the tee on the lower radiator hose (that is input to the water pump). So i continued to hack off almost all of the tube. Then drilled & tapped(1/2"NPT) the rear psgr block-off plate, installed a 45* 1/2"pipe 'street elbow', with a 5/8" hose nipple ,and ran a 8" hose [to the stubby aluminum tube from the silicon rubber hose to the heater] to feed the heater core from the rear inspection plate. Cleaned up the psgr head surface, made a jam by the trans dipstick. Well worthwhile, i think , to drain heat from rear of the hotter head. {My driver side head had 2 cracks, psgr side 10 cracks}.
Afterward, it occurred that better technique would have been to run a pipe tap right into the hole in the head that the inspection/block-off plate covers, and then use studs/bolts to block off the tapped holes.
If i were to rebuild a 6.5L, i'd vote similar to Grape--1" pipe(if fit, else 3/4") from rear each head , 1/2" tee from psgr head to heater; both 1" hoses merge to 1-1/2" runs forward to second thermo, tees into top hose feeding radiator.

[grape]

I don't think my dual stat housing is going to fit in my old bodystyle truck on the rear of the heads, the firewall gets in the way. Besides i got it all bolted up on the engine stand and forgot.........i'm not using an elecltronic transmission yet so i have to have the one plate for my tv mount. Thank god i'm finally getting rid of the rear vacuhm pump thanks to the local bone yard that sold me a serpentine set up.

[gmctd]

No intent of discouraging inventive ingenuity here, but, other than Anxious Subman's '99, it may be noted that vehicle representation in this topic is consistantly prior to the '97 factory coolant upgrade scheme.
Mine's Dec '94, has the upgrades, as have most of yours.

Question - were Hummers ever availed of the '97 scheme, due to cooling system layout?

I will say, that if it can be proven, by temperature readings across the heads, cylinder by cylinder, that temps stabilize and equalize across each cylinder with any or all of these mods, then I've got some 304ss fittings needing a noisy home.

Per-cylinder head temperatures are of concern, where bypassing the heads with a less-restrictive flow path may allow hot spots across the combustion areas.

The passages thru the head gaskets are .125" or so - very restrictive, even tho the between-cylinder deck passages are 1/2 - 3/4", IIRC.
The rear deck passage is approx 1/2 x 1 1/2" rectangle, with no restriction in the head gasket.

It can be seen that almost all coolant flow thru the head is thru that rectangular passage at the rear of the block.

The 6.5 water pump is not cranking 7000rpm, as in a racing engine, where cavitation can play a big part when coolant passages in block and heads restricts flow back to the water pump inlet. Pump spins faster than coolant can flow, so provide an external path to improve flow back to the pump.

Yeah, I know - lots of you guys already know this stuff, but a lot of folks with cooling questions do not.

The intake-side head area is not good for spot temp readings, as no water passages exist around the intake ports.
They are, as a matter of fact, constantly bathed in heated engine oil and vapors on their way thru the CDR system.
Better readings would be taken in injector\glow plug area.

Skeptical, yes, but always open to factual results.

[ 02-26-2004, 03:08 PM: Message edited by: gmctd ]

[JeepSJ]

I'm looking for blank plates. I think the hole for the glow plug controller would be too big. You don't want to allow too much flow from there or you risk overheating the center cylinders. Fluid is going to take the path of least resistance. In stock form, water is pumped into the front of the block, travels rearward, up into the head then back out of the crossover (yes, some does work its way up into the head around the front cylinders as well). You still want to maintain the same flow path. The idea of the bypass at the rear of the head is to allow a little more coolant to get around the back of the block. Personally I wouldn't take coolant out of there with anything bigger than a 1/4" line.

[tom.mcinerney]

Thanks for your considerations, GMCTD, and JeepSJ.
I will rethink my efforts....

[Uncle Wally]

I was thinking about this last night after I read the whole post.

Has anyone taken a cracked block and some heads and experimented with coolant flow to see how much really flows and where?

Here was what I was thinking. Apparently the holes on the block that feed the head are different sizes. I would assume to control the amount of flow to certain parts of the block. I think it would easy enough to hook up a plate and mount some flow gauges to see how much the block actually flows. Use a water pump and then rig up an electric motor that would spin the setup close to 2000 rpm. Use a garbage can with a bung in the bottom as the reservoir and then pipe the water from the flow gauges back to the garbage can. Kind of a backwoods setup, but I think it might be informational.

Then install the heads and mount plates at the four corners and see how much flows out of each one. Same setup with the garbage can.

I would expect that to make sure that everything cools as it should the flows should be fairly evenly balanced out. One might be able to experiment a bit with enlarging the holes in the block that feed the heads. My assumption would be that the heads have all the same size holes as you should be able to bolt one head on either side of the engine. I would think if someone has an old cracked block, it would be fairly easy to set something like this up.

Once all that was figured out, it would easy to designsome tubes that come up the intake valley and tie into the coolant crossover. One would probably have to 'tweek' injector lines to minimize interference. That would keep the housing the high point in the system, allowing one to bleed it fairly easily.

If you really wanted to see how this would work in a closer to real world scenario, one could plump some tubing that would allow the use of a 'tiger torch' in each cylinder. That way you could introduce some heat to the block to see how much of a difference it really made on balancing the cooling out, if it really is a problem.

Any inputs on this idea?

Waldo

[More Power]

The idea of adding hoses to rear of the cyl heads in an attempt to improve cooling comes up about once a year. Taking coolant out at that location only makes things worse.

As was mentioned earlier, coolant flow begins at the water pump and is pumped into the cylinder block which flows primarily front to rear, then up into the rear of the cylinder heads, then forward to the thermostat housing. There are a series of smaller coolant passages in the head gasket that allows some coolant to shortcut, but the largest cooling passages and the coolant flow is at the rear of each head.

Taking coolant out at the rear of each head will reduce the coolant flow that flows forward inside each head.

Secondarily, I've seen a number of #6 & #8 cylinders that were washed out. In the cases I saw, it was due to dirt ingestion. The flow path through the turbo and intake manifold deposits the majority of the grit in #6 & #8.

MP

[ 02-27-2004, 08:32 AM: Message edited by: More Power ]

[gmctd]

Absolutely!

And, no - I am not one of the Boss's lackeys! ;)
I have never seen evidence of, or even suspected that, Jim had any requirements or desire to have any lackeys, but I want to cover any points of contention, in order to establish purity of opinion.

And, I am unanimous, in that. ;)

The key to preventing hot spots is to improve coolant flow\circulation thru the block AND heads.

Removing the bypass valve from the thermostat improved block\head circulation.

That, and adding the 130gpm water pump increased b\h circulation by around 75%.

Adding the dual t-stat increased radiator flow by around 10%.

(Don't remember the exact values, but MP stated them in his article on '97 coolant system upgrades.)

Adding blades to the fan increased air flow thru the radiator.

The combined package allowed a power increase in '99.

Modified fan clutches are available which stabilize to overall lower temps under loaded conditions.

Good ideas, Uncle Wally - I'd like to see results from that type of testing.

[ 02-27-2004, 12:53 PM: Message edited by: gmctd ]

[tom.mcinerney]

Thanks, Jim; thanks again, J.D!

[john8662]

Thanks More Power. Like I mentioned in my first post in this thread, it was an idea that I was told by a reputable diesel mechanic as a way to help the problem with "washed out" cylinders. His theory was that the cylinders were getting too hot. I'll also agree that it probably was due to dirt. The airbox's in the 92-96 6.5 trucks/subs/etc were a BIG source of problems as they didn't seal good and were difficult to know if you had a positive seal w/o taking the box out. Thats why I have fixed that problem by installing an air-box from a 97+ rig with the ROUND positive seal airbox. This is something that a lot of people that had their vehicles serviced by "jiffy-lube" probably had problems with, as they don't care about your truck. Thats why I do ALL of my own maintenance like oil changes. As I mentioned in the first post, the mod was a trial for before I had the 97 cooling mods. I left it in place, but have been having second thoughts since doing so. Thats why I posted here on the page to see what others that had better knowlege of the internals of the engine would have to say about it.

For the majority, most are concerned with what you are concerned about, that it could (and probably is) robbing cooling potential from the heads, or head in which it is installed in. Also, most that replied to the post had the idea that it probably doesn't hurt anything, but there is no proof that it does actually help. The "mod" is also in the way in my opinion. When I get the opportunity to take off the intake manifold, it will be in the way. And it sure is one more thing for the Stealer to look at going around when I take the rig in for the warrantied IP (its getting one before it goes out of warranty whether I have to sabotage it or not). smile.gif

One thing for sure, the tubing I was advised to use is in my opinion TOO large, and could very well have an adverse affect on cooling performance. A smaller hose could be used, but who knows if this actually works or not. And the chosen way of tapping into the suction port on the waterpump may not be the right place, as some pointed out. Some people that have offered their opinions say that if it were to help that it would be best to be connected to the thermostat housing. I don't know. I appreciate everyones input in this matter, I like the comments either for or against the mod, because thats what I needed to make my decision.

My final last questions I have concern the durability of the 6.5L.

Approximatly how common is it for having excessive wear on the #8 cylinder in the 6.5 engines that either fail or were replaced under warranty?

And finally, are the later engines (1997 and beyond) that fail and were replaced under warranty have the same washed out cylinder problem or was it truely fixed? If it was fixed, was it fixed by, A: better air filtration, or B: cooling mods? I am aware of other reasons for replacement (like cracked blocks due to large oil spray holes), not conerned with that right now.

[ 02-27-2004, 08:16 PM: Message edited by: john8662 ]

[gmctd]

I just dug out my DP Feature Article volumes (and like my Playboy subscription, I get them for the articles, not the pictures!), and More Power did at least three articles on the '97 coolant system upgrades, and variants.

Maybe enough interest\votes would get them re-posted in the Blast from the Past reprint series.

[ 02-28-2004, 06:07 AM: Message edited by: gmctd ]

[toyboxrv]

One thing people tend to ignore on the bypass mod, although I look at it as a balance flow mod, is that the size of the passage in the block from the water pump is bigger than the size of the passage going into the crossover. The crossover is restricting the amount of water that the pump can supply to the block. A simple mathematical calculation can show that a 1/2" fitting in the rear plates will equal out the difference between the two. In that case the pump will flow slightly more and not be a problem with restricting cooling flow through the heads. I have a year and a half of using this mod and my heads are not cracked and I have a measurable change in the temps at the rear of the engine. No one who claims this is a bad idea can show me that it doesn't work. I used to get as much as 215* on the truck gauge and a scary 235* on a gauge with a sender mounted on the outside rear of the passenger head. The most I have seen since is 210* and 220* for the two different gauges and to me that is an improvement. Since the two cylinder banks are fed separately from the pump and act like two 4 cylinder engines from a cooling standpoint, I can see no reason why the #8 cylinder would be any hotter than the #7. Coolant doesn't flow from one side to the other, only to the back through the block and back to the front through the head. Maybe a 3/8" line could acheive some results, but my opinion is a 1/4" line wouldn't make enough difference to be worth it. :D

[gmctd]

1. Agreed, the pump\block port and head\crossover port are of inequal sizing.
Restriction can be good in some instances, not so good in others.

A pump flowing 20gpm in a free-flowing 20gpm circuit will not develop any pressure, as an example.
The pumped fluid will just circulate at the speed of the impeller - no restriction to volume velocity, no pressure.
(Yes, I'm disregarding fluid\wall interface friction)
When pump output flow-rate exceeds thru-put flow rate, excess volume stacks up as pressure.
Pressure is needed to raise coolant boiling point above the operating temps in the cooling system.

2. Agreed that rear block and head on pass side can exhibit hotter temps than at the front.

3. Agreed that temps will drop at the rear block\head by utilizing an external bypass.

The contention being , and with no intent to single any post out -

The passenger-side head does exist in close proximity to turbo exhaust manifold, where radiated heats can approach 1200deg, and so may exhibit higher coolant temps than driver-side system.
Put a pot of water on a hot stove, and an unusual thing begins to happen - the portion of the pot adjacent to to the radiated heat begins to increase in temperature, along with the contents, therein.

That coolant from the engine rear is mixed with coolant via the between-cylinder block-to-head passages as it flows frontward thru the head. These passages also serve to prevent steam generation at various "normal" hot-spot areas in the block and heads.

The temp sender in front left head gives averaged coolant temps from left side only - we do not have any indication of right-side temps for comparison.
Far as averages go, we all know that a man standing with one foot in a bucket of boiling water, the other foot in a bucket of ice water, is on the average fairly comfortable.

Temps must be compared with same sender\gage assembly, or the baseline is faulty.
If the temp\gage assembly measuring front head temps is used for comparison, it must also be used for rear head temps to establish any actual difference, or initial temp spread.
Even if that gage is not accurate (and we all know the factory gage seldom is - mine is 10deg higher than the PCM ECT sender), a comparison baseline must be established.

Temps must then be taken across each cylinder, with that same gage, to insure the modification does not result in any temperature increase per cylinder.
20deg coolant drop at the rear cylinder results in how much temp increase in cylinders # six\four\two and five\three\one.

Use any preferred probe\gage or digital instrument, but it must be used for all readings.
Probes for digital gages are reliably accurate, so multiple probes can be used with the same instrument for precise comparison.

I am skeptical, for currently known, proveable reasons.
I would like to see the individual temps which factor in to result in the "average" temp, before and after any modification.
Convince me with numbers.

I believe, as do others here, that any head cracking was due to overheating and hotspots caused by the recirculation bypass shut-off valve in the '97-back cooling scheme - as the t-stat opened, it also functioned to close the bypass.
That, and high coolant temps from radiator blockage by accumulated dirt, leaves, grass, etc, which MP addressed in the cooling system maintanence article.

Again - and this is due to the low-rpm nature of a Diesel - improved constant coolant recirculation, increased circulation by a larger pump, a more aggressive fan - water-pump rpm is low, so add more blades to increase air flow - are proven methods to stablize temps in this engine.

[ 02-29-2004, 01:30 PM: Message edited by: gmctd ]

[grape]

I just love that everybody who has no personal experience with bringing water out of the back of the head on their own engines, has so many facts as to why it doesn't work. Yet the people that actually do it and note temperature drops can't be right. Race cars do this on every engine I've ever seen...yea yea yea I know, cavitation......you have any idea how far underdriven our water pumps are to free up power and to keep them from cavitating? When we turn a short track engine 9200 rpm we are underdriving the waterpump 5-1. This works on every engine I've ever seen, no reason it won't on these stupid things. Connect the rear of the heads to the thermostat crossover and the cylinder head temp WILL even out.

[toyboxrv]

I'll agree gmctd that I would have to use the same gauge to determine the exact amount of change from front to rear. I saw a drop of 15* at the rear from prior to the mod and even a drop at the trucks gauge indicating an overall reduction in engine temps. I already had a dual t-stat crossover and high volume water pump and was looking for something more and found it. The hot turbo may add some heat to the passenger side, but I haven't seen anyone demonstrate how much. I guess I'll just stick with it until I can see a downside. I'll agree with grape that those who speculate know even less than those who try it. :D

[gmctd]

Anyone with roundy-round experience care to jump in here?

It's not about dampening enthusiasm or initiative.

I would like a definitive answer as to why a 600hp engine, turning 9200rpm, would not have coolant circulation problems from a water pump turning only 1800rpm (5 to 1 underdriven), without a bypass from the rear of the engine to improve circulation.

That's quite a thermal load to be dumping into the water jacket.
Even water jackets originally oem-designed with racing in mind.

'Course, Chevy couldn't admit to it due to corporate pressure, but the small- and big-blocks were designed for something over and above street use.
And Dodge. And Ford.

And Detroit Diesel - not!

Not a good idea to dismiss the inherent differences, particularly in the heads.

Again, I plead my case. I'm game - show me the numbers.

And, don't forget, guys - I not only drive a Diesel truck....I built the truck I drive.

[toyboxrv]

Those numbers are 235* max without the mod and 220* with it being measured by the same gauge at the same point. I also believe, although I did not time anything pre-mod, that it returns to normal temp quicker after cresting a hill. You accept that the outlet from the head at the crossover is smaller than what the pump can deliver to the block. I don't see why allowing the output to match the input capability, which could mean more flow in, could cause temps to rise or reduce cooling in part of the head. I used two lines to the t-stat housing, but I have since found a y-block fitting at Jeg's that has two 10AN connections and one 12AN that would couple the two lines from the head and send one line to the t-stat housing. There are also smaller blocks available for those that would think 1/2" from each head would be too much. I have seen some postive results with this mod and have yet to see real proof of any problem with it. :D

[Barry Nave]

GMCTD

wow :cool:
Your the man :D
How can any body not hear you :confused:
I can't wait for my temp probe to come :D

[JohnC]

It would be interesting to see what happens to the temperature of the water exiting the front of the heads before and after the mod.

[gmctd]

Thanks, Toyboxrv - believe me, I do not doubt your numbers or the results.

Here are some numbers for your consideration, also.

Specifically, coolant passage dimensions:

Waterpump passage is 1.125" wide x 0.625" deep
Timing cover thru block is 1.250"
Front, passsenger-side head is 1.125 x 1.250"
Front, driver-side head is 1.125 x 1.125"
Crossover manifold is 1.250" dia, each side.

Differences in head passages are due to casting tolerances - yours may be better or worse.

As mentioned previously, an examination of coolant passages would reveal some areas which should be modified for improvement.
Equalizing the flow thru and out of the heads would be a good start.

Prior to completing '97 cooling mods, a summer trip towing a loaded tandem axle trailer resulted in coolant temps in the gage red area. No a\c, 55mph, the temps never dropped in over 200 miles.
FSD failure shortly thereafter.

After completing the modifications, another summer, same trip, same trailer heavier load, 200lb passenger, burned the a\c the entire trip, 55 - 70mph, temps never went over the hash mark above 200deg, would drop below 200deg on flat runs.
Tech 2 indicates engine coolant temp to be 10deg less than the temp gage indicates.

That's my story - more on racing a low-speed water pump, later.

[ 03-01-2004, 06:31 PM: Message edited by: gmctd ]

[john8662]

Geez, Looks like this got serious! As far as I am concerned, I've got some testing to do, I am getting a digital thermometer to see how things add up. But for others looking at this post just reading, I would just say stick with the 97 cooling mods. If it's good enough for a 300hp 6.5TD in Tough Guys truck, then its a good solution.

[gmctd]

To restate, simply -

The rear coolant bypass works as stated, whether in a racing engine, or a Diesel engine.
Install the bypass, rear cylinder temps will drop.

Contention -

What effect does the bypass have in the area aound the pre-combustion chamber and the valves, noted for cracking in the pre-'97 turbo Diesel heads.

Removing any coolant flow from those areas cannot be a good thing.

Para-phrasing JohnC's statement, monitoring temperatures where coolant exits the heads would establish a reliable reference.

[toyboxrv]

So far I would have to say there has been no effect on potential cracking of the head. It has not been established that there is any reduction in flow through the head by installing a bypass, or as I see it a balance flow line. A 1/2" hose has a sectional area of .2 square inches, while the 1.25" block inlet has close to 1.25 in area. The difference between the crossover area and the block inlet is about .2, resulting in a reduction of resistance and potentially an increase in total flow.The passages through the block to the head are greater than what the pump can deliver. What regulates flow is what can be delivered from the pump and what can leave the block and go to the t-stat. This mod isn't the first thing anyone should do, that would be the high capacity mod, the Dmax fan and different clutch and maintaining a clean radiator. The balanced flow cooling mod adds an extra amount of insurance against reaching those high temps that can lead to serious problems. :D

[gmctd]

Final clue to the puzzle -

C\K1500 trucks were shipped with TDC Offset at -1.5 degrees, desired timing at +8.5deg.
Some C\K2500's were to same specs.
Power band moved upward to higher rpm range.
Maximum advance at highway speeds in 18 to 20deg range.

This setup was due to the light-duty nature of the series, which employed an EGR system to control emissions.
Light loading - more emissions.
Recycled exhaust gases lowered combustion temps, reburned combustion byproducts.

Light loading - less heat into the cooling system.

C\K2500 and C\K3500 series were set to -0.5deg TDC Offset, desired timing at +3.5deg, no EGR.
Power band was set for max torque at lower rpm.
Specs were set for heavy loads and heavy towing.

Heavier\high loading - less emissions.

Heavier loading - more heat into the cooling system.

High loading - much more heat into cooling system.
Tremendous heat into heads via pre-combustion chambers.
Normal air flow thru cylinders does not effectively remove combustion heat from the pre-cups.
Requires high coolant flow thru the head to offset this tremendous thermal loading.

Ever wonder why 6.5TD heads crack?

Head surface is flat across valves area, pre-cups are inserted into recess between valves, centrally, but to the exhaust side of the head - glow plugs and injectors are inserted into pre-cup chamber.
It's called Indirect Injection.
The 6.5 is also higher compression than direct injected Diesels.

Comparisons cannot be made to cylinder heads designed for gasoline fuel.

Nor, in my opinion, should any cooling modification proved workable on gasoline engines be installed on the 6.5L turbo engine, without extensive testing.

Possibility the 1/2-ton series will incur little or no damage from the modification, due to light loading?
Caveat emptor.

Probability the 2500\3500 series will?
Caveat emptor, squared.
(If you're moving heavy loads with your 1500, you're invited to join this group)

Do the tests, monitor the coolant temps exiting the head before and after modification, under no load, and heavily loaded road conditions.

Pull the load up a 6% grade for about 5 miles - longer or steeper, if you dare. ;)

Prove it works.

Post favorable results, I'll duplicate it on my 3500 truck, in stainless steel.

I rest my case.

Note: This is not directed at any specific person that posted, but to anyone still interested.
Combat is not encouraged. ;)

[ 03-05-2004, 01:09 PM: Message edited by: gmctd ]

[toyboxrv]

I don't feel the need to prove to your standard that anything works. So far you haven't shown why it wouldn't. I have driven my truck with a 6k 5th behind it up long steep grades in 90* + temps and have seen a reduction in water temps both at the truck gauge and at a gauge in the rear of the passenger head. I have also seen a quicker drop in temp after cresting a hill. This mod, as I earlier stated, has been on for 1 1/2 years without a problem. It has always shown, in different conditions, a reduction in temps. Just because I have not set up multiple gauges to monitor changes in a manner that suits you does not mean it doesn't work. You can stick with whatever you want for your truck and I'll stick with what I have shown to work on mine. :D

[GMC Hauler]

gmctd,

Is the bypass valve on the thermostat the spring protrusion from the botttom of the stat? How exactly does the bypass valve work and under what conditions?

From what you have written, it occurs to me that pre dual thermostat setups (me) should switch to a thermostat from a later non bypass valve type. Is this correct?

[Cowracer]

FYI for all thats intersted

I am setting up a similar deal on my engine, but instead of taking water out of the back of the heads, I will be injecting cool water directly from the water pump into them.

I agree with MP that taking water out will do more harm than good, but I belive that doing it the other way will provide many benefits.


If it works, call me Hero...
If it don't, call me Stupid

And Yes GMCTD I have seen it on circle track engines BOTH ways.

Tim

[john8662]

Cowracer,

Wow, this is bringing back an old post, no problem though.

I just wanted to see if you've talked to Bill Heath about his Balanced Cooling System. I talked to him about the project and it sounded like a good idea that was tested and actually worked.

I'm consider this mod.

About the previous mod, I won't be installing it on the new engine until I have reason to believe that it can do some good. I'm going to mount two water temp senders in the ports on the back of the heads and measure temperature. If I see a reason to that the temps are that much hotter in THAT area, then I'll put the bypass setup back on. I don't think that the #7 gets hot at all, and according to Heath, thats confirmed. He said that the system is imbalanced in the first place, so #'s 6,8 are going to run hotter anyways.

[Cowracer]

Hey, I didnt bring it back, GMC Hauler did! (Just between you and me, I think too much time underwater in a steel pipe made him a little "special") :D :D

If I understand Bills system, It may have some benefit, but I think my way is better. Besides my way will be free with parts graciously dontated by my work. wink wink

Tim

[john8662]

Whichever route you take, prove that it does work. I'm going to rig up some senders for before and after results, I have to "sell" it to myself that I'm doing more good than harm. I don't plan on doing this whole engine build up again in the near future, and I'll kick myself if it was my fault (intead of GM's).

[GMC Hauler]

:D

I get a little bored at work. We are watching our boat (read: sewer tube) being cut into razor blades. Someone has to baby sit the ship, which gives me some spare time to review old posts and ask more questions. It's always good increase your knowledge.

Submariners do make for interesting friends and aquaintences. :D