6.5 dual stat cooling upgrades back in stock!

[Kennedy]

Just like the title says, we now have the kits on the shelf once again. There are some "out in left field" vendors out there who seem to think that a single stat and restricting the bypass is the answer, but I'll say it point blank nothing could be further from the truth.

[ronniejoe]

I have also advised several people (who have asked me) to avoid the bypass restrictor that is out there. This is a horribly bad idea.

[Robyn]

These clowns with the ANTI DUAL STAT BS have got to be Smoking something...

I agree 100% with John and RJ...

The better coolant flow with the dual stat setup is likely the single most beneficial change in the 6.5 cooling system ever made. (PLUS THE HO PUMP)

The new heads produced by AMG are certainly a game changer when it comes to having better flow in the heads.
When I built the last engine for the Dahoooooley I used an AMG block and AMG heads and then reused the single stat xover and the standard pump (Pump was new)

The rest of the cooling system was fresh. The AMG engine has always ran much cooler than the GM iron ever did..
GOTTA BE THE FLOW THROUGH THE CASTING ?????

[sctrailrider]

Yea once my P400 is done I will be looking into this more...

[trbankii]

There are some "out in left field" vendors out there who seem to think that a single stat and restricting the bypass is the answer

Yet I'll pretty much guarantee that not a single one of them feels that downsizing your exhaust is the answer to better performance. You know, by the same reasoning, holding the exhaust in the engine longer should make more power, shouldn't it?

[Robyn]

There has been lottsa snake oil fixes for the 6.5 and nearly all of them are worthless wastes of time and $$$$$

The 6.5 has always been a problem child when it comes to keeping the temp in check in hot weather and when the rig is worked hard.

Every truck we have had here has to some extent been fussy in hot weather, even when new.

The best fix was to get the fan clutch working before the coolant was at 230 F and then the beast was OK.

[arveetek]

The 6.5 has always been a problem child when it comes to keeping the temp in check in hot weather and when the rig is worked hard.

Every truck we have had here has to some extent been fussy in hot weather, even when new.


With the dual thermostats, HO water pump, modified fan clutch, and all-aluminum radiator, I finally feel comfortable when towing and no longer have to keep my eyes glued on the temperature gauge. I still have to back off the throttle some on mountain passes, but now the engine stays pretty much a constant temperature under load: right in the middle of the gauge.

Casey

[Robyn]

Pretty much how it's done.

Why did GM release these trucks with such a sketchy cooling system ????

Even the New 6.5 rigs I have had were marginal in the hot weather...

[Yukon6.2]

Why did GM release these trucks with such a sketchy cooling system ????


Bean Counters R the Devil.:rolleyes:

[Robyn]

YESSSSSSSSSSSSSSSS...The beanies saved GM a few $$$ but cost them millions of $$$

For very little more per unit cost the 6.5 could have been a great engine, but with a few strokes of the beanies pen the 6.5 was reduced to a very marginal piece at best.

So much could have been done differently and was not.

Poor castings
Poor crank
A real POS injection system.
A marginal cooling system

Had the 6.5 been built up using better iron, a deep skirted cross bolts block, heads with better materials and far better coolant flow and add a few more head bolts just for good measure...then toss in a top notch forged crank.

The electronic injection needed at least several more months of serious refinement before it was ready for prime time.

Ahhhh yesss.....

Could have been...GM's legacy.


Maybe VW was not all wrong in their approach to dealing with things.:rolleyes:

[DmaxMaverick]

......Had the 6.5 been built up using better iron, a deep skirted cross bolts block, heads with better materials and far better coolant flow and add a few more head bolts just for good measure...then toss in a top notch forged crank.......

Ha! You just described what became the Duramax.

[Robyn]

Yup...pretty much.

Could have saved GM the second nasty black eye after the Olds oil burner debacle.

Ah well...the beanies know best it would seem.

[Robyn]

There were a few experimental engines made during the run up to the 6.5... even one with direct injection.

Obviously the beanies nixed them too.

[More Power]

With the dual thermostats, HO water pump, modified fan clutch, and all-aluminum radiator, I finally feel comfortable when towing and no longer have to keep my eyes glued on the temperature gauge. I still have to back off the throttle some on mountain passes, but now the engine stays pretty much a constant temperature under load: right in the middle of the gauge.

Casey

A better turbocharger is the final piece of the engine cooling puzzle.

All of the cooling system upgrades promoted here through the years did solve the engine temperature problems, but only a better turbo can reduce EGT (which indirectly affects ECT in a max power setting).

Try a Holset HX-35 (1994-98 Dodge Cummins app) for a step up from the GM-x series turbos or install a Holset HX-40 for a more dedicated heavy hauler.

[ronniejoe]

One must keep in mind the origins of the 6.5. The 6.2 L Diesel was designed to be an economy oriented offering, not the current beasts which are the product of renewed power wars between the big three. GM did learn its lessons from the Olds 350 Diesel. The 6.2 was designed as a Diesel from the ground up by the Detroit Diesel Allison Division. However, GM at that time did not believe that the economics of the automotive and light truck market would support the cost of typical medium/heavy duty Diesel engine technology. So, they tried to apply automotive gasoline engine design practices to Diesel engine design for automotive use. They largely succeeded with the 6.2 L NA engine. While it was not a powerhouse, by nearly all measures, it was very successful.

The year 1990 was an inflection point for the Diesel engine market in light trucks. This saw the introduction of the Cummins 5.9 L Turbo Diesel into the Dodge Ram pickup. Interestingly, Cummins offered the engine to GM first. (Interesting side story... I know some of the engineers at Cummins in Columbus, IN and one of the test operators who worked on their 5.9 L project. They built a late 80s 2500 GM truck with Cummins 5.9 L in it and took it to Detroit to give a demonstration to GM brass. GM turned them down cold. Next up? Dodge. They built a Dodge pickup and Chrysler was hooked. They didn't have a Diesel to compete with the GM 6.2 L or the Ford 6.9 L or 7.3 L IDI Diesels at the time.) Although the power offering was a meager by today's standards 160 hp, it was significantly higher than the 6.2 at 135 hp (18.5%). My uncle bought an early 1990 Dodge Cummins Diesel. I rode in that truck when it was new, just a few weeks after he got it and I said, "This changes everything. If this engine was in a good truck, it couldn't be beat."

Where GM screwed up is in not seeing where the market was going after the introduction of the Cummins in the light truck market. They tried to keep up by boring the 6.2 L to make the 6.5 L and adding a turbocharger. The problem is, they really screwed up the turbo match. The turbocharger is the biggest driver for the 6.5 L engine's overheating problems. It's simply too small on the exhaust side. Even though the early 6.5 L Turbo Diesels were competitive on advertised power, they couldn't deliver that power reliably over the long haul.

The reliability problems with the introduction of the DS4 pumps hurt badly as market share disappeared. The introduction of the electronically controlled turbo wastegate, while potentially a good idea, was also botched as the control system would dump boost right when the engine needed it most. Additionally, the blocks were not designed to handle the stresses associated with turbocharged operation and main web cracking became a problem.
These combined issues soured GM management on the engine (and Stanadyne, by the way) and the rest is history.

Ford initially tried to respond to the Cummins in the same way as GM by adding a turbocharger to their IDI 7.3 L Diesel. This was a short lived stopgap measure as they saw the future and developed the Powerstroke Diesel and introduced it in 1994 to compete directly with the Dodge Cummins. GM didn't wake up until it introduced the Duramax Diesel in 2001.

[ronniejoe]

Back to the dual thermostats...

The bypass restrictor that is available is a really bad idea as I said before. Ask yourself the question, "When the thermostats are closed, how does the coolant circulate through the engine?"

[Robyn]

Great info RJ

History has kept GM in the backseat for most of the diesel pickup era for sure.

It would certainly be interesting to fully understand why the powers at be made the lame decisions they made...

[arveetek]

I often remind folks who might look down on my 6.5L diesel, that my rig is currently 23 years old, and that the basic engine was designed in 1981! I, for one, think it's doing pretty good for running so strong at 340K miles, and on a basic design that is now 37 years old!!

Sounds like a turbo upgrade is in my future if I want to keep towing. For local trips, things are pretty good now. But our attempt at towing a 4,000lb camper to Yellowstone this summer didn't pan out (OEM radiator blew apart), and I had to keep an eye on EGT and ECT when pulling a mountain grade. I can definitely tell she did NOT like pulling those long, steep grades! We don't have anything like that here in SW Missouri.

Casey

[Kennedy]

I see Walt has a single stat that supposedly outflows the dual stats. How a conventional reverse flow even comes close to the flow area of a balanced sleeve is beyond me.

On the bright side I think we are past the rear head bypass BS that a certain vendor has at a Rendezvous a decade plus ago touting as the latest. I also hope we are past the 70% flow bias in the OE water pump BS, but I do see Leroy has a "balanced flow" water pump :rolleyes:

[ronniejoe]

I see Walt has a single stat that supposedly outflows the dual stats.

I've posted these pictures before, but here goes again.

http://www.schoolcraftpowertrain.com/Pictures_&_Data/IM001290.JPG

http://www.schoolcraftpowertrain.com/Pictures_&_Data/IM001291.JPG

http://www.schoolcraftpowertrain.com/Pictures_&_Data/IM001292.JPG

http://www.schoolcraftpowertrain.com/Pictures_&_Data/IM001293.JPG

Look at the difference in size of the bypass flow passages. The single thermostat crossover thermostat was the "block off" type as seen here:

http://www.schoolcraftpowertrain.com/Pictures_&_Data/IM001294.JPG

This stat closes off the bypass when it is fully opened. The valve adds blockage to the through-thermostat flow when opened, however. The dual stat housings did not use this type of thermostat for two reasons that I can see: 1) eliminate the blockage caused by the valve structure seen the photo (the valve would also need to be much larger to close off a larger bypass port, thereby increasing blockage) 2) use the same part number in both locations for the dual stat housing.

The bypass restrictor reduces the bypass flow area to significantly less than that for the single thermostat housing. This will significantly reduce the bypass flow and when the stats are closed, will cause the pump to operate at significantly higher back pressure than it was designed for. This is because flow through the pump is throttled by the restriction. This causes the impeller to churn the fluid because very little is leaving downstream. This causes an increase in the local temperature of the fluid and can lead to cavitation, which causes erosion on the impeller and pump housing degrading its efficiency. The pump is being damaged under these conditions.

One could, in theory have a single thermostat crossover that flows as well as or better than the factory dual thermostat crossover in bypass mode, but it is difficult to see how a single standard thermostat could ever flow as much as two thermostats in through-thermostat mode. Does he have some custom thermostat made out of unobtainium that provides double the flow?

I consider this the same as his many other difficult to swallow claims.

[Robyn]

A flux capacitor....that's the ticket :D:D

Once installed between the two wires on the CTS everything is just sweet...:rolleyes:


I'm with ya RJ
ANSWERS TO THOSE QUESTIONS are "Unobtainable" ;)

[phantom309]

On the bright side I think we are past the rear head bypass BS that a certain vendor has at a Rendezvous a decade plus ago touting as the latest.

I'm almost afraid to ask why the four corner cooling mod is no good,?
I ran two coolant lines from the back into the themostat housing,.i drilled and tapped etc,.. inmho it made a difference,.
I read quite a bit from the aussie forums and their conclusions and their mods were different than north american mods. Drilling extra steam holes in the fire deck etc,. Australia has some very hot country ,.
The gist of their idea was the extended soak time of the coolant in the heads from the long trek from front to back to front again, caused steam bubbles leading to water pump cavitation. I am definitely not as smart or as innovative as Some people on this forum,. But for me the extra lines helped my old dually

Nick

[ronniejoe]

I ran two coolant lines from the back into the themostat housing,.i drilled and tapped etc,.. inmho it made a difference,.

Please take no offense to any of this because none is intended.

If you did as you say here and allowed coolant from the block off plates at the back of the heads to go directly back to the front crossover, then you removed cooling flow from your cylinder heads.

The coolant leaves the pump outlets and enters the front of the engine block on both sides. It is pushed to the back of the engine while absorbing heat from the cylinder walls. At the back of the engine, it flows up through the kidney shaped core passages into the heads and is pushed forward absorbing heat from the combustion chambers along the way to the exits into the crossover/thermostat housing. There are core passages in both the heads and the block decks between and around each of the cylinders which could allow coolant to short cut the circuit. Some does, but it is limited by the head gaskets, which have very small metering holes in them which line up with the larger core passages. These holes are necessary to keep air pockets from forming during initial fill of the engine with coolant. Without these small holes, air could be trapped between cylinders near the deck surface. With them, air is displaced through the holes, into the heads and out the bleed port on the thermostat housing allowing a complete fill of the system. Once full and in operation, these holes are no longer necessary, but they cannot be removed or closed without significantly increasing the complexity of the machine, so they allow a very small percentage of the coolant to short cut the circuit.

The cylinder heads are obviously where the most of the combustion heat energy is concentrated, therefore, this is where the coolant picks up most of its heat energy in the flow circuit. By allowing a significant portion to bypass the heads and return to the thermostat housing, you have reduced the flow through the heads where it is needed most.

I can see the potential for lower coolant temperature readings at the gage sender location, however, that are not indicative of the actual coolant temperature at other places in the engine. The gage sender is located near the front of the driver side cylinder head. Theoretically, with the as engineered cooling circuit, this is where the coolant temperature should be highest as it is near the end of the loop after passing by all of the heat transfer surfaces in the engine. There should be no higher temperature any where else if there are no blockages or other flow problems. Since you have bypassed a significant portion of the coolant flow which should pass through the heads and routed it to the front of the engine, the gage sender will likely see a lower temperature because of heat transfer through the fluid to the cooler fluid entering the crossover from your bypass set up. The head loss in your bypass lines is likely much lower than the head loss through the passages in the cylinder heads, so you might even be seeing partial backwards flow of bypass coolant into the front of the cylinder heads. This likely means that some coolant is dead headed around the middle cylinders of each head. If you could put your sender between the number 5 and number 7 cylinders (or the number 6 and number 8 cylinders), you would see significantly higher temperatures which would likely scare you.

If you want to improve your cooling system, figure out a way to take the pump discharge and push it through the heads first and return it from the block. This is the "reverse flow" approach that is common on newer engine systems. This is a difficult task with the existing architecture of the 6.5.

I recommend that you remove your bypass lines and plug the holes that you made and let your cooling system work as it was engineered to work.

[ronniejoe]

Poor crank

The cast cranks in the 6.5 get a bad rap that they really don't deserve. They're actually pretty good. The crank that I used in my Suburban until right before it was totaled was from the warranty engine that was installed at about 65,000 miles right after I got the truck. I ran it in that engine almost 100,000 miles until it broke the number 6 piston. I had that crank index ground (.010" under) and balanced and installed it in the new engine that I wrote the articles about. It ran another 125,000 miles and would still be running if a catastrophic oil leak had not caused a spun #7 rod bearing.

During that time, the truck was towing something, usually heavy, for at least 50% of the time. With the new engine, I had boosted power to a level not seen in any other on-road 6.5 L Diesel, and I used it.

I have replaced it with a new forged crank from GEP which is now in my K3500 Dually.

Kennedy has said this and I have come to the same conclusion: broken crankshafts in these engines are secondary failures that are the result of main web cracking which allows excessive deflection of the crank. If the main webs don't crack (splayed mains), the factory cast crank can take a lot of abuse with no issues.

[sctrailrider]

I see Walt has a single stat that supposedly outflows the dual stats. How a conventional reverse flow even comes close to the flow area of a balanced sleeve is beyond me.

On the bright side I think we are past the rear head bypass BS that a certain vendor has at a Rendezvous a decade plus ago touting as the latest. I also hope we are past the 70% flow bias in the OE water pump BS, but I do see Leroy has a "balanced flow" water pump :rolleyes:


Sad thing is uniformed people are buying it.. I think it's high time someone with the data speaks up on the various other forums...

[Kennedy]

On the single stats how about removing the bypass closing disc from the thermostat altogether? Only the early 90's trucks had them and they had the most issues albeit at higher power levels than their predecessors. The water pump can easily move may times more water than the bypass circuit can flow.

Still not a substitute for the dual stats but...

[phantom309]

The water pump can easily move may times more water than the bypass circuit can flow..

Ronnie this is where, in my opinion i think that the water pump has plenty of flow, when the stats are closed you are allowing for a quicker route time thru the engine,.cold water water from the rear of the heads mixes together with hotter water from the front of the heads right at the tStats, keeping the stats closed untill a more even temp of water (i.e even after mixing the stats open at set temps) what is attained in the use of a water pump that flows a lot more volume if you choke the flow? proper proof of either theory would come down to measurements.
flow from front of heads with no rear head bypass lines and water exit temps
flow from head of heads with rear bypass lines and water exit temps
time to achieve working temps
engine would need to be on a water dyno to simulate steady load.

jmho
nick

[ronniejoe]

Did you read my post?

You can do whatever you want with your truck. I'm just offering you some sound advice. When you overheat the center two cylinders on each bank and gall a piston or two, then maybe you will appreciate the engineering behind the cooling system.

I've explained very clearly why you might be seeing lower temperatures on the gauge with this setup. I've also explained why the temperatures at the longitudinal center of each head are likely significantly higher than what your gauge is reading. For this reason, the "bypass cooling" is a bad idea and I recommend that you remove it. It is your truck, though. You do what you want.

[phantom309]

Did you read my post?

You can do whatever you want with your truck. I'm just offering you some sound advice. When you overheat the center two cylinders on each bank and gall a piston or two, then maybe you will appreciate the engineering behind the cooling system.

I've explained very clearly why you might be seeing lower temperatures on the gauge with this setup. I've also explained why the temperatures at the longitudinal center of each head are likely significantly higher than what your gauge is reading. For this reason, the "bypass cooling" is a bad idea and I recommend that you remove it. It is your truck, though. You do what you want.

Yes i did read your post,. I also sense your lack of patience regarding someone else's view point that does not correspond to your own,.

No malice intended.

Your view point of the 4 corner coolant flow, gives the impression that the block will be starving for coolant due to added coolant flow paths
Basic hydraulics , liquid will always choose the easier path. Do you think the two lines from the back of the heads carry more flow than what is passing to the front of the heads thru the head castings? Do you believe that the water pump will not produce enough pressure/volume to support two extra paths of flow? The extra flow paths are being re-introduced to the t stat housing thereby keeping pressure up and keeping exit volume the same. If the rear lines dumped into the rad i could see your point.
Would the water pump rated at X flow, flow more or less depending on its restrictions?
The idea of drilling the fire deck for better flow volume of coolant has merits too ImHO. According to the author in australia that wrote about it, it was a necessary mod to finally cure his overheating problems. Head gaskets already had the holes but the block didn't. He increased volume by decreasing restriction
Factory engineers work within time and cost restraints. Improvements have been made to numerous systems on vehicles to address engineering shortcomings.
Small oil capacity, small turbo, small water pump, inadequate air flow across the rad etc etc , all things that have been addressed and are now common place upgrades and improvements.
Yes it is my truck,. Yes i will do as i want,. With or without your respect.
I respect your knowledge and pioneering accomplishments,. But unless you have documented measurments of temps and flow volumes your theory has as much merit as mine inmo.
Carry on, i'm finished here,. I'm off to re read why the back two pistons had to have more clearance due to excessive heat or something like that.

[More Power]

More info on bypass cooling:
https://www.thedieselpageforums.com/tdpforum/showthread.php?t=25230 (https://www.thedieselpageforums.com/tdpforum/showthread.php?t=25230)