Transmission Thermostat Question

[Curt]

Have you ever measured the temperature of the trans fluid in the pan?

How do you know you need a cooler that enormous?

Hummer H2's have a built in transmission temp gauge in the cluster. When towing on hot summer days pulling a 5000 lb trailer it'll reach a temps of 240*F+. Been that way since 2005 when we bought it and haven't had any transmission failure yet. Yes, I know... yet.

What tranmission are we talking about here?

4L65e in a 2003 Hummer H2.

I recommend this cooler.

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The sending unit is mounted in the provided "T" fitting in the cooler line coming out from the transmission.

The pan location for the sending unit can lead to a false sense of security.

An aggerated absurd example follows;

The fluid comes out of the transmission at 4000 degrees Fahrenheit.

Then it goes through a cooler the same size and shape as Nebraska.

It dumps into the pan @ -40F.

Your pan mounted temp sender says 180F.

You never knew it got hot.

Which cooler do you recommend? The link leads to a transmission temp gauge.

The transmission temps I'm basing my needs for cooling off of is the factory transmission temp gauge located in the cluster of the H2's. It sounds presumptuous when I say this, but I don't intend for me to come off this way. But you would think GM would make sure the transmission temp gauge would read accurately, right?

What's most important is the temperature of the fluid being picked-up by the trans pump to be squirted through all the trans passages--valve body, converter, clutch packs, governor, etc.

THAT fluid should be in that 160--200 degree F range.

Putting the temperature probe in the hottest fluid produced by the trans leads to panic, which leads to people buying MUCH more trans cooler than they need. Which leads to higher Corporate profits, but not much improvement in actual trans life.


I was told a slightly-different version of this way back when I was in trade school. At that time, it started at 170, not 200. (So by 190 degrees, trans life was already halved.) I've found versions of this that go all the way back to the late 1950s when ATF was still based on whale oil.

I don't think it's accurate any more. Fluid, trans seals, etc. have improved. Modern transmissions routinely go 200,000 miles or more, with reasonable maintenance (when they're not based on the "700" or "200" design--which isn't really a fault of the fluid or fluid temperature.)

Here's an example:

http://txchange.com/heatchrt.jpg

If that temperature/trans life correlation was EVER accurate, I think that NOW it's mostly scare-tactics to sell people stuff they don't really need.


Probably works great for trans coolers. Kinda thinking about getting one, now that you've pointed it out. OTOH, I've got no trans problems to blame on too-cold fluid. I've popped a couple of TH700s in my K1500 which I blame on the basic, weakass TH700 design; and one 4T60E that I blame on flat-towing the car too far when the car broke down.

I'd be scared to death to use it on an engine oil cooler. 3/8" inlet and outlet would murder oil pressure in a full-flow system. My L29 uses 1/2" tubes to the internal radiator-mounted oil cooler.

I agree, high temps kill transmissions. I've experienced in real-time how quickly temp will smoke a transmission. That's going down a rabbit hole of a conversation though haha. As for that derale thermostat, I can confirm it works great. I have the Derale 13011 on my suburban and has performed flawlessly. Would highly recommend that setup. More info on my transmission cooler setup on my truck here:https://www.gmt400.com/threads/time-to-get-serious-with-4l60e-4l65e-cooling.50138/

As for the Hummer, it's on 38x15.50x18's. Just driving around town trans temp will sit at 195*F. On top of that, it's a boosted 6.0 pushing power through a 4L65e. Been going strong for 50k miles now with these temps and being boosted at birth, will correct the transmission if/when it goes.

They make coolers now with the t-stat built in . They flow 1/4 of the cooler until temp opens the internal valve then its 100% cooler flow . Easy to plumb and less work and fittings .

As said what are current temps ? 40k cooler on a 4L60 based trans in my opinion is a lot . If your making that much heat there is other things to look at first .

Right now the max cooler size I could squeeze in that tiny space would be 22"x8.5x2". I haven't had any luck finding a cooler with a built in t-stat yet.

Current temps are about 250*F on the trans temp gauge when towing. Coolant temp sits at about 235*F and will continue to climb if I don't let off during a hill climb. These temps are achieved during hill climbs on 100*F+ days. The truck is supercharged pushing 5 lbs of boost, has a 4" lift on 38's, towing a 5000lb load + cargo. Funny enough, it sounds like my luck with temps and towing go hand-in-hand leading to all fingers pointing at my driving style, but I've followed all the driving techniques that I know of to not only prolong a life of a 4L6xx transmission while towing, and keep temps as low as possible.

The real issue is having trucks that are not 100% focused on towing only. We don't tow enough to warrant a tow dedicated vehicle.

 

[stutaeng]

I didn't know the Hummers ran the 4L65e? I thought they all ran the 3L80 (TH400) and the later ones ran the 4L80e? Or is that the H1 or the original military spec vehicles? The HMVEE or whatever they are called? I don't anything about them.

My front door neighbor had one. I'm guessing it was the H2? They look extremely heavy now that I think about it to be running that transmission...5 psi of boost, lifted and 38" tires? Towing 5k lbs climbing mountain passes! Geez! Are you actually trying to kill your transmission?

What is the curb weight of that vehicle anyway? Sorry, I'm not helping...maybe regearing to help keep the transmission temperature lower? What are your highway RPMs? How fast are you driving? Have you tried slowing down to see if that helps?

250F sounds a bit too high to me. Maybe add the deepest pan you can find to hold more fluid? Tow in 3rd? Run an aux. cooler inside a Jeti cooler filled with ice? I dunno.

Edit: You have the Tow/Haul mode right?

 

[Schurkey]

1. First and Foremost: Make sure the converter locks up whenever possible. Towing in 3rd with a locked converter is WAY BETTER than towing in 4th with the converter not locked.

The 700/4L60, '60E won't lock the converter in 2nd (my '700 sure doesn't, I don't know about the '65E.) However, I've heard--but not confirmed--that the 4L80E can lock the converter in 2nd. I'll have to play with my K2500 to see if that's true. Never noticed it locked in 2nd, anyway.

2. Your truck weighs...7K? Plus a 5K trailer. Add 3K for giggles. You need a cooler "rated" for 15K, maybe 20K, not 40K. Retain the OEM cooler and you're golden.

 

[tayto]

never bypass the radiator cooler, unless its a quick fix to get home. always run rad first then external cooler. if you live in winterland, put a thermostat between the rad and the. external cooler, so on warm up it bypasses the external cooler. this is for quicker warm up times. sorry if same points have been said already and I'm repeating.

you are on borrowed time with a heavy vehicle & forced induction on a 4L60E. I would personally being saving up for a 4l80e. i like the 4l60e and they can be built, but it is the wrong application here...

schurkey: your 700r4 will lockup in 2nd if you wire it that way. 4l60e and 4l80e have had the ability to lock up in 2nd since TBI era. however i have never seen a factory calibration that does but you can modify to enable it.

 

[stutaeng]

Here are the specs for your transmission: https://www.dieselhub.com/trans/4l60e.html

Says input torque rating is 380 ft-lb. I believe the stock LQ4 is rated for 360 ft-lb.

Under 5 psi of boost: 360 ft-lb + (5/14.7)x360 ft-lb = 482 ft-lb. (360 + 122 = 482)

These just basic theoretical numbers and altitude will obviously bring those numbers down, but you get the idea. You are outside of the factory rating of the transmission by a good margin, very likely why you are overheating it.

You are probably under the GVWR of 8,600 lbs, but may be close to the GCWR of 15,500 lbs. Probably need to weigh your rig to know for sure.

 

[Curt]

I didn't know the Hummers ran the 4L65e? I thought they all ran the 3L80 (TH400) and the later ones ran the 4L80e? Or is that the H1 or the original military spec vehicles? The HMVEE or whatever they are called? I don't anything about them.

My front door neighbor had one. I'm guessing it was the H2? They look extremely heavy now that I think about it to be running that transmission...5 psi of boost, lifted and 38" tires? Towing 5k lbs climbing mountain passes! Geez! Are you actually trying to kill your transmission?

What is the curb weight of that vehicle anyway? Sorry, I'm not helping...maybe regearing to help keep the transmission temperature lower? What are your highway RPMs? How fast are you driving? Have you tried slowing down to see if that helps?

250F sounds a bit too high to me. Maybe add the deepest pan you can find to hold more fluid? Tow in 3rd? Run an aux. cooler inside a Jeti cooler filled with ice? I dunno.

Edit: You have the Tow/Haul mode right?

It's sad that GM put a 4L60/65e in these things, but it's the truth. Lord knows I wish this transmission isn't there. We bought the truck boosted from a buddy who owned a custom speed shop out here back in the day. I have no information as to whether or not the transmission is built, I was too young to ever ask about it and we've lost contact since. My guess is the transmission must have something done to support all this, otherwise I can't see how it lasted this long. Like I said, truck has 50k miles on it, I'd say about 50% of those miles are towing, and it runs great... minus the temps of course.

We've thought about regearing, but again we'd also prefer a vehicle we could use on the highway to cruise across the country if we'd like, without screaming the whole way there.

As far as curb weight with all the equipment in it, it's a heavy mf. If I had to guess I'd say somewhere in the realm of 6800-7000 lbs curb weight.

Following the towing speed limit, or following traffic it doesn't make a terrible difference. And as for tow/haul mode, I find it way too aggressive to bear it necessary. Sure it prevents the trans from going into OD and controls shift patterns, but I can do that as well. Plus, using the gear selector (3-2-1 on the shifter) I can let off throttle before shifting if needed to prevent more heat buildup.

1. First and Foremost: Make sure the converter locks up whenever possible. Towing in 3rd with a locked converter is WAY BETTER than towing in 4th with the converter not locked.

The 700/4L60, '60E won't lock the converter in 2nd (my '700 sure doesn't, I don't know about the '65E.) However, I've heard--but not confirmed--that the 4L80E can lock the converter in 2nd. I'll have to play with my K2500 to see if that's true. Never noticed it locked in 2nd, anyway.

2. Your truck weighs...7K? Plus a 5K trailer. Add 3K for giggles. You need a cooler "rated" for 15K, maybe 20K, not 40K. Retain the OEM cooler and you're golden.

Yeah, I always listen for TC lockup. Heat builds quick if you don't pay attention to that.

I'm confused with the second statement, why would I retain the OEM cooler? If the Tru-Cool 40k isn't needed, shouldn't I just step down to the 20k (LPD 49201) or 30k (LPD49211)? I disagree that the OEM cooler is sufficient for this rig.

never bypass the radiator cooler, unless its a quick fix to get home. always run rad first then external cooler. if you live in winterland, put a thermostat between the rad and the. external cooler, so on warm up it bypasses the external cooler. this is for quicker warm up times. sorry if same points have been said already and I'm repeating.

you are on borrowed time with a heavy vehicle & forced induction on a 4L60E. I would personally being saving up for a 4l80e. i like the 4l60e and they can be built, but it is the wrong application here...

schurkey: your 700r4 will lockup in 2nd if you wire it that way. 4l60e and 4l80e have had the ability to lock up in 2nd since TBI era. however i have never seen a factory calibration that does but you can modify to enable it.

Yeah, I'm not a fan of bypassing the radiator cooler. I understand people have problems with the internal lines rotting in the rad, but that hasn't happened to me before.

Trust me you're preaching to the choir here. I'm just trying to make do with what I got right now. Just like I did with my truck, upgraded coolers, then when it's time upgrade the trans. I'd have to really look into CA restrictions at that point.

Here are the specs for your transmission: https://www.dieselhub.com/trans/4l60e.html

Says input torque rating is 380 ft-lb. I believe the stock LQ4 is rated for 360 ft-lb.

Under 5 psi of boost: 360 ft-lb + (5/14.7)x360 ft-lb = 482 ft-lb. (360 + 122 = 482)

These just basic theoretical numbers and altitude will obviously bring those numbers down, but you get the idea. You are outside of the factory rating of the transmission by a good margin, very likely why you are overheating it.

You are probably under the GVWR of 8,600 lbs, but may be close to the GCWR of 15,500 lbs. Probably need to weigh your rig to know for sure.

I agree. Hence why I see a pretty dire need to throw some coolers on it. I have my suspicions that the transmission is built, but cannot verify that information. I can't see how this transmission has lasted this long otherwise. Still shifts great and feels like a brand new transmission. Even did a trans filter & fluid change last year and the fluid was perfect, no funky smells or colors.

 

[Schurkey]

I'm confused with the second statement, why would I retain the OEM cooler? If the Tru-Cool 40k isn't needed, shouldn't I just step down to the 20k (LPD 49201) or 30k (LPD49211)? I disagree that the OEM cooler is sufficient for this rig.

Yeah, I'm not a fan of bypassing the radiator cooler. I understand people have problems with the internal lines rotting in the rad, but that hasn't happened to me before.

What I meant was to keep the OEM in-radiator cooler, but add a 15K--20K GVW-rated add-on cooler.

I don't think you need a 40K cooler when your vehicle is less than half that weight.

You're not burning-up the fluid as-is. Dropping the in-pan temperature (which is where GM puts the stock sensor) a bit might be nice. If this were me, I'd carry along an infra-red thermometer, and check the pan temp so as to compare to the OEM sensor/computer data stream readout.

Are you saying that there's already an add-on external cooler in addition to the in-radiator cooler? In that case, find out the size / capacity of the existing external cooler, and double it. Maybe that gets you right back to the 40K GVW cooler you said you wanted to begin with.

 

[sweetk30]

i have a 80's k30 with a th400 and 4.10 gear with stock size tires 31.5" and i pull a 7k-10k trailer a bit with it and also plow snow with a 8ft and 9ft wide fisher snow plow .

i have ZERO ext cooler and i have a B&M trans gauge inline of the hot out from the trans and pulling long steep hills i can get up north of 260* but the whole rest of the time its normal as the engine cooling temp is .

i prefer knowing how hard i am working the trans ( hot line out temp ) over the average temp ( the pan ) so i can lay off before its to far gone .

 

[Frank Enstein]

What's most important is the temperature of the fluid being picked-up by the trans pump to be squirted through all the trans passages--valve body, converter, clutch packs, governor, etc.

THAT fluid should be in that 160--200 degree F range.

Putting the temperature probe in the hottest fluid produced by the trans leads to panic, which leads to people buying MUCH more trans cooler than they need. Which leads to higher Corporate profits, but not much improvement in actual trans life.


I was told a slightly-different version of this way back when I was in trade school. At that time, it started at 170, not 200. (So by 190 degrees, trans life was already halved.) I've found versions of this that go all the way back to the late 1950s when ATF was still based on whale oil.

I don't think it's accurate any more. Fluid, trans seals, etc. have improved. Modern transmissions routinely go 200,000 miles or more, with reasonable maintenance (when they're not based on the "700" or "200" design--which isn't really a fault of the fluid or fluid temperature.)

Here's an example:

You must be registered for see images attach

http://txchange.com/heatchrt.jpg

If that temperature/trans life correlation was EVER accurate, I think that NOW it's mostly scare-tactics to sell people stuff they don't really need.


Probably works great for trans coolers. Kinda thinking about getting one, now that you've pointed it out. OTOH, I've got no trans problems to blame on too-cold fluid. I've popped a couple of TH700s in my K1500 which I blame on the basic, weakass TH700 design; and one 4T60E that I blame on flat-towing the car too far when the car broke down.

I'd be scared to death to use it on an engine oil cooler. 3/8" inlet and outlet would murder oil pressure in a full-flow system. My L29 uses 1/2" tubes to the internal radiator-mounted oil cooler.

There are larger ones for engine oil

 

[Curt]

What I meant was to keep the OEM in-radiator cooler, but add a 15K--20K GVW-rated add-on cooler.

I don't think you need a 40K cooler when your vehicle is less than half that weight.

You're not burning-up the fluid as-is. Dropping the in-pan temperature (which is where GM puts the stock sensor) a bit might be nice. If this were me, I'd carry along an infra-red thermometer, and check the pan temp so as to compare to the OEM sensor/computer data stream readout.

Are you saying that there's already an add-on external cooler in addition to the in-radiator cooler? In that case, find out the size / capacity of the existing external cooler, and double it. Maybe that gets you right back to the 40K GVW cooler you said you wanted to begin with.

That makes more sense, thank you for the clarification. I'll have to take my IR thermometer and aim it at the pan next time we use it.

Yes sir, there is an external transmission cooler from the factory. It's a dinky little thing... without even towing with a stock H2 people complain that it is insufficient. I'm not surprised though, a big truck with this trans behind it. I'll do some research and see what the capacity of the cooler is.
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Thank you everyone for your input, it helps a lot.