Transmission Operating Temps

Volucris · April 21, 2009

I have a 2007 GMT 800 'Classic' 4WD Crew, LS version. It has a 4.8L and a 3.73 rear end. It does not have a tow package, and therefore no auxilliary transmission cooler. I need to pull a trailer once or twice a year, maybe 4,000 pounds at most. I'll be pulling it up and down mountain passes as well.

I called four GM dealers around here and every single one of them told me I do not need an auxilliary tranny cooler, and this was after I told them I wanted them to put the GM one on.

I ordered a scan guage II and it should be here in a few days. I'm going to use that to monitor my tranny temps to see what it does operate at when not pulling a load, and especially when I am pulling a load.

My question is, has GM or anyone actually published any data on the normal operating temp of a 4L60e? There are all sorts of opinions out there, mostly don't go obver 175 for long. But, if that's true, why don't I hvae a tranny cooler? If it just goes through the radiatior, it either heats it up or cools it down to around 190. Does the fact that it has Dexron VI for the fluid make a difference?

Anyway, I was looking at adding an aftermarketcooler and looks like a pain in the rear if you don't have one at all. and, since four different GM dealers said don't bother I'm inclined not to. It does get very cold in the mountains in the winter (-20) although it gets in the 100's down low in the summer.

Andy advice? And, any actual numbers?

Thanks for the info.

C & A s Dad · April 21, 2009

If GM's "official #s" mean anything, the last time I read any hard data on GM's trans temp warning light, it said the light came on at 250 degrees. Too hot for me and for most anyone I have ever heard comment on this. You can search some of the cooler suppliers and they offer some charts showing the temps where damage begins occuring.

IMO, I am not so concerned about "official #s". I want my fluid and trans to handle my towing needs and last as long as possible. For a small investment in a good cooler, I added some extra insurance for my transmission.

For me, I want my trans temps to run below 200 when towing. My cooler handles this with ease with my temps running mid 160s towing a 6500 lb camper in 95+ degree outside temps.

Dex VI certainly will handle more temp than dino fluid.

One last thing. Adding your own aux cooler is not big deal at all. Even without an OE cooler, adding one is not a big job. If you elect to look into this, send me a PM with your e mail address and I will send you some good pics of my upgrade.

You will need a good stacked plate designed cooler which is the same design that GM uses as OE. With your climate variance, you will likely want to look into a thermostat or a cooler with a stat built in.

txab · April 21, 2009

Listen to Trey. He's the resident expert on coolers.

C & A s Dad · April 21, 2009

Thanks Darral,

Not sure I would go that far.

I simply have done a good deal of research and reading on coolers and have installed one one every vehicle I have ever driven.

Obviously I believe in a good trans cooler and still am of the opinion that a Pick Up should not be offered by the Mfg without some type of aux cooler.

txab · April 21, 2009

Well, maybe not "expert". But you have posted enough real world experience and personal knowledge on the subject that has been very helpful to many on this board.

nonotme42 · April 21, 2009

For what it's worth, and all the research I've done on the matter, I agree wholeheartedly with everything Trey stated.

Trey, do tell, what exact cooler are you running that keeps you in that perfect temp range, even under such unfavorable conditions as described? Also, what exact type of device are you using to monitor transmission temps?

crepitus · April 21, 2009

For what it's worth, and all the research I've done on the matter, I agree wholeheartedly with everything Trey stated.

Trey, do tell, what exact cooler are you running that keeps you in that perfect temp range, even under such unfavorable conditions as described? Also, what exact type of device are you using to monitor transmission temps?

i would like to know this as well. and also for those that already have a cooler it there an aftermarket cooler that can just be swapped out for the stock cooler.

txab · April 21, 2009

Here's a pic of Trey's setup. I believe he told me it was an 11" x 11" x 3/4" I know that it is a stacked plate cooler

txab · April 21, 2009

Another

brims · April 21, 2009

You will need a good stacked plate designed cooler which is the same design that GM uses as OE. With your climate variance, you will likely want to look into a thermostat or a cooler with a stat built in.

This is the first time I've seen someone mention using a thermostat, I've been thinking it's a good idea for some time.

I would like to upgrade my aux cooler and install a thermostat. I went on a trip this last weekend, I was doing about 80 mph and was seeing low to mid 180 on the cooler, at one point it got to 194 degrees which I did not feel to comfortable with.

I see with Trey's setup, the ports are sideways, is there any advantage to that over the GM way where they are on the bottom?

nonotme42 · April 21, 2009

And I should probably add in a photo of my current stacked plate cooler...its a B&M 70264 SuperCooler 11 x 6 x 1.5"

But I definitely need a temp gauge.

That one pictured before looks like a Hayden/Imperial?

Volucris · April 22, 2009

Trey,

I'll definitely send you a PM soon. I'm travelling right now. I'd like to see the other side of your radiator.

Does the BM super Cooler have a good reputation. Supposedly they have the ports drilled so the fluid will bypass the cooler if it is too cold. Which brings up the other question, how cold is to cold?

C & A s Dad · April 22, 2009

My cooler is a CARQUEST 77423 and is appx 11" x 11" x 3/4". Hayden is our supplier of these stacked plate coolers. The B & M is a very high quality piece as well but from my research, the 3/4" thick models are more efficient and less restrictive than the 1.5" models. Not that the thicker model is bad becasue it is not. However, according to an engineer I spoke with at Hayden, they dropped the thicker models for this reason. You will also not that GM stopped using the thicker models as well with the introduction of the 1999 800 series trucks.

I personally do not run a thermostat because of the warmer climate I live in. If you live in a climate that sees 100+ in the summer and single digits in the winter, you will need a stat to regulate the flow in the winter so the fluid will warm up.

How cold is too cold? I wish I could give an engineers answer but all I can tell you is what I found out from two people I feel have a good understanding of transmissions. One is the owner of a local Coleman Taylor trans shop with over 30 years experience and the other was an engineer for the company who provides our reman transmissions. They both told me that ATF must get warm enough to flow easily through the system. If I remember correctly, they felt anything over 125 was fine. I have heard some people say that the tq converter will not lock at temps this low. I cannot speak for all vehicles but my converter will lock at temps below 125.

If I am not mistaken, Tru Cool is the company that offers a cooler with engineering designed to allow for bypass when the fluid is colder and thicker. I would imagine True cool supplies B & M with their coolers.

Rat4go · April 22, 2009

After the last dialog on cooling etc, I've been doing some more searching. I have not found a 'how hot is too hot' number, and everything I have found suggests that the recommendation is a 'lifetime' average number recommendation, which doesn't say that you can't or shouldn't run 220F or hotter, it just says if you run that hot regularly, you need to change fluid more often.

After thinking about it, probably every other fluid in the truck runs 220F or hotter when towing. Coolant fans don't come on 'til near that in some vehicles if the AC is off, engine oil would likely be similar temp to coolant, I've seen folks that have axle temps in their road race cars and see temps in the HIGH 200s, even with a cooler, and don't worry too much about it. All these fluids have one sort of magic additive or another added to the base fluid and all these fluids come into contact with seals and gaskets of some sort, so I am still wondering why ATF is any different. I suppose if my trans was shifting every 10 seconds and the temps were really hot, I'd be more concerned about the temps at the clutch plates and try to prevent the shifting, and I certainly agree that if you see higher temps all the time, you either need to change fluid more often or add cooling or both.

I've also learned a bit more about aftermarket coolers and some of the terminology.

Stacked plate is a cooler that has multiple 'parallel' plates (and thus parallel paths) for the fluid to flow. These plates have stuff inside them to 'swirl' the fluid so that you don't get cool fluid near the metal, and hotter fluid flowing down the center, making the cooler less effective. To much of the 'stuff' insided can cause restriction, so you need to be careful (or add more plates to the stack). The other type of cooler is kinda like a zig-zag pipe with fins on it...almost like a fat trans cooler line. They tend to be more restrictive as they also have 'stuff' inside them to help heat transfer, but all the fluid needs to pass thru this single tube instead of multiple plates.

I think it was mentioned by torqfaze (and I've confirmed with a manual) that the fluid going thru the cooler is used as lube for gearsets and bearings when it gets back to the trans with the 4-speed. You don't want too much restriction or you kill lube.

I also learned that many transmissions have a 'fail-safe' mode that eliminates cooler flow if the trans controller line pressure request is greater than the pump can provide (mostly a problem at low engine speeds so you need to be careful about that, too.

Someone asked about port orientation on a cooler (side vs top or bottom). From what I gather, it's slightly better to have the ports on the side, with the inlet being lower than the outlet as this helps push air out of the cooler. There was some other speculation that this was BS, so use with caution.

Lastly, the comment about aux coolers in the winter is a good thought for a couple reasons. I found out that Toy actually has an ATF WARMER (!) on their truck. Probably for getting it to flow better when the truck is first started for fuel economy. Best I can tell, it's thermostatically controlled....wonder what temp it tries to get the ATF before it quits warming? This would be pretty interesting info to have....I haven't found it yet.

If I were to put a non-oem aux cooler on my truck, I'd think hard about either covering it in the winter (in northern areas), or as has been suggested, looking for a bypass of some sort. I don't think you want to REGULATE flow thru the cooler (cooler flow = lube, regulated lube is bad in my book) , but to BYPASS the aux cooler 'til you need the extra cooling. Trey mentioned both concepts in his post and I think I know what he meant, but......

Volucris mentioned a cooler with drilled bypass ports.....what keeps these from bypassing HOT fluid, too? This would help from a flow perspective, but would make the cooler not as good a cooler, right? Seems like the cheap way out and would make me look for a different concept.

I didn't find anything for how cold is too cold other than folks from Minnesota posting about starting their trucks at -40 and having every pump on the truck mad (noisy) for the first few minutes 'til things warmed up. Long ago, I heard that you wanted oil to get to at least 170F occasionally to evaporate any fuel that washed down the cyl walls, and above 200 to get ride of condensation. A trans won't have the fuel issue, but if an engine can have condensation, why not a trans?

I'm still looking for answers to my ATF temp questions, but figured I'd comment on what I'd found so far. Sorry if it rambles.

brims · April 22, 2009

I've read several places where the minimum ATF temp should be 150 degrees so the seals aren't hard and work as they are supposed to. I have seen some guys running at 120 or something while towing, I think I even saw someone say they normally ran under 100, I don't see how that would work very well.