Dual t/stats: 180 & 195 or two 180's?

[arveetek]

I have a dual thermostat housing ready to be installed on my '95 6.5L. I want to purchase new thermostats before installation. I've done some reading, but haven't come to the conclusion yet as to whether to install two 180 degree thermostats, or one 180 and one 195.

This is for a mostly stock, high-mileage 6.5L that does some towing now and again. I have a 16' camper for vacations and a 16' flatbed that I use to tow my Jeep. The camper causes more of a heating problem than the Jeep, due to the larger wind drag.

I will not be installing a high-flow pump as of yet.

Casey

[DennisG01]

I can't directly answer your question, but I can offer what I've been doing. From what I understand, two 195*'s allow the engine to be in it's optimum temp range for power and efficiency. Even before I had the 18:1 engine I ran two 195's and never had an overheat problem (although, because mine is a '98, I do have the higher flow pump). If you're overheating with the weight you're pulling now (relatively light), I'd wonder if the radiator and other stuff up there are at least partially plugged with debris.

What does your engine temp gauge get up to before swinging back down?

I see you have 3.42's - what RPM are you doing your towing at?

[arveetek]

I'm not overheating, but getting warm. For everyday driving, the gauge stays pretty much at 210 with the stock single t/stat housing. When towing, it gets over 210 quite a bit and makes me nervous.

The engine seems to run coolest and happiest when towing in OD at or near 1900 RPM.

I'd prefer to have a steady temp. It doesn't take much extra throttle input for the needle to start climbing up.

Casey

[6.5TDTahoe]

get the operating temp to create stable temp to keep from temperature flucations. The iron likes being @ the op[tium temperature.Absolutly do not use 2 different temp stats. I strongly advise installing every 1999/2000 year cooling system upgrade. Also use the DuraMax fan blade .Simple,eh!

[DennisG01]

That's interesting that you've found 1900 to be good. From my experience (and what I've learned/read), I've found a few hundred RPM's higher than that to be ideal. But that's towing 10,000lbs and 1900 just doesn't provide enough power for hills.

210 is certainly on the high side for normal driving. If you haven't already, definitely take the fan shroud off and look very closely at all the radiators/coolers up there. Look between the fins and between coolers.

I don't think you're going to be able to get the temp's to stay constant. I think it's just, good or bad, the design of our system. Case in point: I put in a new (rebuilt) engine (totally clean). While the engine was out, I replaced some of the coolers and cleaned the rest (inside and out) REALLY well. I even have the Kennedy HD fan clutch. This was probably about the ideal situation to test this temp swinging thing. I still get a swing. About the highest I'll see (when towing heavy) is maybe 215*. But it comes right back down.

[handcannon]

I'm not overheating, but getting warm. For everyday driving, the gauge stays pretty much at 210 with the stock single t/stat housing. When towing, it gets over 210 quite a bit and makes me nervous.

The engine seems to run coolest and happiest when towing in OD at or near 1900 RPM.

I'd prefer to have a steady temp. It doesn't take much extra throttle input for the needle to start climbing up.

Casey

First, running at 210* for everyday driving is too warm. It should not be running that warm, something is wrong. As suggested previously, you may have a buildup of crud between the radiator and AC condenser and oil/tranny coolers. Pull your rad and make sure the rats nest that builds up there is cleaned out. Then use some cleaner and get all the crud out of the rad fins. If it has been a while since last done, take it to a rad shop and have them clean out both the interior and exterior of the rad. Making sure the cooling stack is very clean is the first step to running cooler for everyday driving.

My rad was damaged so I found a copper/brass rad from a 93 that was in good shape and had it checked. For DDing I run in the 195* + area. When towing is the only time my temps climb now. To help control towing temps I ended up changing to a 2000 model year balanced flow pump, got Heaths' HD fan clutch, Heaths' bypass system restricter, and an 02 DMax fan blade.

My towing temps are better now. However, on a long uphill pull that will always increase temps I've never heard the fan come on so I'm questioning the Heath fan clutch. I wish there was a more positive system to be sure the fan clutch would work like it should.

Don

[HH]

FWIW - On my 1993 K3500, I am running dual 180 stats in my 18:1 engine, I never see 210*. I am running the stock fan, and an aluminum core radiator.

[trbankii]

I'm a bit curious about the reasoning of considering mis-matched thermostats? Is the thought that two 180's opening together is going to cool things too much? If both opening would cool it too much, then they'd close again.

As I say, just curious on the reasoning.

[arveetek]

Maybe my mind is getting fuzzy, but I was sure I had read a long time ago to put in different temp t/stats, so that the higher temp would control temp for normal driving, and the lower temp would open sooner to allow more flow? Maybe I'm dreaming.

I decided to go with two 190* stats, as that seems to be the recommendation these days.

Casey

[DmaxMaverick]

I'm a bit curious about the reasoning of considering mis-matched thermostats? Is the thought that two 180's opening together is going to cool things too much? If both opening would cool it too much, then they'd close again.

As I say, just curious on the reasoning.

No. While this causes wild temp swings, rarely actually seen on the gage, it isn't a matter of "too cool". Offset stats are, by far, the best option. I, and every late model engineer, agree. Having a high and low stat allows for more gradual coolant temperature control, and more efficient/effective fan clutch engagement. If anyone "needs" two (or one single) lower temp stat to keep the temp under control, this is only masking a larger problem. The outward indication a cooling system is healthy is NOT an ability to keep the temp low, but to manage the coolant temp effectively during extreme conditions. Almost never is a thermostat the problem component, but gets the blame/replacement most often.

The initial reason for GM changing to dual stats in 1996 was solely for greater flow, while using standard size thermostats. Later it was discovered that a progressive thermostat arrangement was far superior. The Duramax thermostats, for example, are not of "standard" size (and NOT of standard price), but were designed as an offset pair. They could have saved significant funds by just using a single, larger, thermostat, since they were using a non-standard dimension anyway. Having 2 is more costly to engineer, produce, and maintain. There are dual-stage thermostats in use for unique applications (non-automotive), but these are significantly more costly than any previous design.

[trbankii]

Ok - so in trying to wrap my mind around this - sort of like a "water hammer" issue with the two "matched" thermostats repeatedly opening up as the temperature rises and then closing as the coolant circulates and cools a bit - whereas the "staggered" thermostats allow some flow as it warms up and then full flow as it reaches operating temperature?

Just something I hadn't seen discussed before. Thanks for the explanations!

[DennisG01]

Verwy, verwy interesting Mr. Wabbit.

So, you peaked my interest in this, Dmax. My system is functioning very well - as far as the gauge goes, I can easily see 185 (consistent) or a tad lower when not towing. When towing, it will bottom out there and then swing back up. So, I'm happy with it.... But if I exchanged one 195* for a 180*, would I see less swinging? Would I run into problems in the winter?

[Robyn]

If you are running 210F there are issues.

IMHO the 190/195 is too stinking hot to begin with. Use two 180F stats and you will be fine.

Now the stock radiators in these rigs are borderline anyway and after a few years of running and "silting in" of the tubes, they become far less efficient at cooling than when new.

The Fan clutches even when new (factory setting) do not really hook up until you get to about 220 and maybe 230.

This is another factory Faux paux. Back in the 80's many people whined when the fan came on a roared even during town driving, so GM in their great wisdom raised the engagement temp WAAAAAAAAAAAAAAAY up in order to stanch the whinning from the customers.

The HO water pump along with the new Xover is good too.

A 190 Stat starts to open at 190F and is not fully open until around 205 give or take

Using a 180 stat allows coolant to start flowing at 180F and the stat to be fully open at around 195F

I would replace that tired on radiator with a fresh new Visteon aluminum unit.

Avoid the cheaper units as many of them are epoxied cores instead of the aluminum brazed ones.

Once the epoxy cracks they leak and there is no fixing them. I paid $270 for a brand spanky new Visteon OEM replacement unit from the local radiator specialty shop up in Portland.

Its amazing just how good at cooling a new radiator is.

The lower levels and the fringe areas tend to silt in badly as well as the tubes all start to collect a coating of crud that insulates them really well.

When this happens the cooling ability is lost and the heating issues start.

During cool weather they do fine, but when summer comes its a losing game.

Once the engine gets the coolant hot it just becomes tougher and tougher to cool it off.

The fact that the factory fan clutch does not really hook up well until the airflow is very HOT makes the issue even worse.

If the fan will come on and really get to hookin it then the temps will fall off really well.

Kennedy offers a Lower engagement clutch for these.

Get the 180Fm stats and have a good working system. Granted the 190/195 temps help promote a better fuel burn and help with emissions, but neither of these things are that important. Keeping the engine cool as far more of an issue than a little bit of economy or emissions.


Missy

[arveetek]

Whew! What a chore! I swapped on the new dual t/stat housing today, and it was more of a job than I anticipated. I'm glad I looked in my Diesel Page manual about this upgrade, or I would have forgotten to plan some time to modify the alternator bracket. It was not as much of a "bolt on" mod as I would have expected. There's a lot of work to be done just to remove the alternator bracket for modifications! Then, the fuel line going to the drain valve cracked, and then the cheesy quick disconnect heater hose fitting snapped off. I was finally able to make it the end, though.

I wish now that I would have gone ahead and upgraded the water pump while I was at it. I already had half the stuff removed to get to it.

I also cleaned out the debris between the radiator and the condenser. I'm anxious now to check my results.

I didn't have enough time to wait for 180 and 195 t/stats, so I just installed two stock 195 stats for now. If I still have issues, I'll wait until after winter to swap them out. Hopefully the two stats will flow better than my original one stat did.

Casey

[trbankii]

A 190 Stat starts to open at 190F and is not fully open until around 205 give or take

Using a 180 stat allows coolant to start flowing at 180F and the stat to be fully open at around 195F

This is more along the lines of how I always understood things to function. So, is there or isn't there a reason to have the thermostats mis-matched?

[arveetek]

I went on a 300 mile round trip this past weekend through the Ozark Mtns to the North Fork of the White River. Pulled some pretty good hills and grades towing my camper, and I was very pleased at the much more steady temps I had on the gauge, even when pulling hard up a hill. And that's with dual 195 stats, and no other cooling upgrades.

Now, I just need to do something about the PCM pulling fuel on the long, hard pulls....

Casey

[DennisG01]

That's great, Casey - it's always nice when you do a mod and actually see some results!

[john8662]

Now, I just need to do something about the PCM pulling fuel on the long, hard pulls....

IAT, or too much boost, You are running a TM...

[arveetek]

IAT, or too much boost, You are running a TM...

Yeah, I'm sure it's the boost. IAT shouldn't be any more than usual, it's more free-flowing than ever. I have the boost set at a max of 10 psi (usually 9 to 9.5 at most). The computer must still not like that.

John Kennedy tells me his TD-Max chip should take care of that problem.

Casey

[john8662]

John Kennedy tells me his TD-Max chip should take care of that problem.


It will :D That's what On my 1995 Sub

[DennisG01]

Ditto what John said, about John...;)

I have been using his programming for years and am VERY happy with it (and the service after the sale).

He also sells a boost fooler which I used for a while (before a full tune) that worked great. But, based on your model year and what John says on his website, you might end up needing two of those (totals $180, then). At that point, it's probably just best to get the chip since you'll get other benefits, too.

[Stratosurfer]

If you are running 210F there are issues.
Now the stock radiators in these rigs are borderline anyway and after a few years of running and "silting in" of the tubes, they become far less efficient at cooling than when new.
Missy
Missy,
I know this thread is fairly old, but your data was super and I wanted to throw in the mix: what does a radiator 'silt in' with? If one uses distilled water and changes the coolant on schedule I'm trying to figure what precisely would be able to block the lower tubes? Gasket material? Rubber material from the inside of the hoses? Iron from the block? All of it together?
I figured if I always used distilled water and changed it on sked that these type of plugging could be avoided. I'm now towing heavy, just bought new 35' Toyhauler that will go out at 9,200lbs empty so I'm forced to fine tune this cooling system. I have the 192 F stats and got up to 220F yesterday on a mild (80F) 120 mile tow yesterday in the Texas Hill country. I just ordered 180F stats and will consider a new radiator. When I'm hill country towing: routine up and down significant grades this summer at 105F ambient I'm afraid I'll be in serious trouble with these 192F Robertshaw stats. But maybe even the radiator.
I'm only towing at 55mph in the hills in 3 at about 2400 RPM.

Mark

[Robyn]

Corosion

There is alway a certain amount of electrolysis going on and other forms of corosion.

The aluminum radiator tubes eventually start to plug up, or they will see a scale build up on the inner surface, which insulates the metal from the heat that the water is carrying.

IMHO the radiators in these trucks are just borderline when new, then add a bunch of years and miles and the cooling ability falls into a sketchy area.

During cooler weather the system works fine, but raise the ambient temps a tad and add all the weight, now the system can't handle it.

Using 180f stats will not hurt, but the systems ability to reject heat is the issue. The reason for using 180 stats is to get the stats open fully by 190 and flowing well.

If the thing is overheating, its the system, not the stats. (unless you have a bad one)


The clutch fan on these trucks is a big issue.

The stock fan clutches are set way too high, and when they get time on them, they really fall short.

One area thats overlooked a lot is the bimetal spring on the side of the clutch that faces the radiator. These can get covered with dirt and crud, especially if the seal leaks a little of the viscous fluid.

If you still have the stock fan clutch, you need to call John Kennedy and get one of his lower temp clutches.

The parts house ones are basic junk, and wont do in warm conditions.

I you reach 210 and the fan is not howling, then your clutch is not working.

That fan should really roar when the clutch is hooked up.

Back in the mid 80's the fan clutches worked right, but under a pull the fans would howl and people bitched about the noise, so GM raised the engagement temps a bit so full clutch engagement did not occur until the thing was way too hot.

If your radiator has a lot of miles, I would recommend a fresh Visteon unit

These are OEM quality and will give you the best you can hope for.

Add a new fan clutch and your issues should be gone.

The 180F stats are a good idea, especially in your area.

Make sure the cooling stack (AC condenser and such) are free of bugs and other debris that can cut off air flow to the radiator.

I see in your Sig that you do have a Kenndy clutch, so the radiator is likely the culprit.


Let us know

Missy

[Stratosurfer]

Missy,
Check this out:

http://www.mishimoto.com/chevrolet-c2500-k2500-w-6-5l-turbo-diesel-engine-aluminum-performance-radiator.html

I don't like the price of $1,000, but if it solved my overheating problems it might be worth it.

Mark