Transmission Thermostat Question

[Curt]

Hey everyone,

I know it's not a GMT400, but I got an '03 supercharged H2 on 38's that is in need of some coolant and trans cooling help. Right now I just purchased a Be Cool 66102 radiator, and planning on adding a Tru-Cool 40k as well. I'm keeping the factory routing (trans fluid goes into radiator, then into trans cooler) even though I know it's suggested to bypass the radiator. I love the thought of having a 40k on the front of that thing, but if I need a cold weather bypass, I'll need to size down the cooler to make space to mount the bypass. Here's a link to a thread with a 40k installed on an H2: https://www.hummerforums.com/forum/hummer-h2-8/h2-external-tranny-cooler-35751/ . If it were like my suburban, I'd just add a thermostat for the heck of it, but unfortunately there ain't much room to mount things here.

My question is: do you think a transmission thermostat would be necessary if I don't bypass the radiator? Around me it gets down to low 30s in the winter and we do take the truck to Tahoe when it's snowing. I'm just thinking the coolant in the radiator should warm up the transmission enough to not warrant a thermostat... right? Interested to hear your thoughts on this.

 

[Frank Enstein]

You're fine. Running it through the Radiator first negates the need for a thermostat.

 

[Schurkey]

If cold weather operation is a concern, wouldn't you route it to the add-on cooler first, then let the radiator warm the fluid before it's returned to the trans?

My truck has been plumbed that way since before I bought it. Winters are occasionally colder than -20F. (Used to be way worse. God bless Global Warming.)

 

[Curt]

You're fine. Running it through the Radiator first negates the need for a thermostat.

Glad to hear it. That was my original thought then I started overthinking it haha.

If cold weather operation is a concern, wouldn't you route it to the add-on cooler first, then let the radiator warm the fluid before it's returned to the trans?

My truck has been plumbed that way since before I bought it. Winters are occasionally colder than -20F. (Used to be way worse. God bless Global Warming.)

That's a great idea, I'll see how much room I have to work with without running too much new line.

Thanks to the both of ya for the input! Going to order that 40K and get to installing it soon!

 

[Schurkey]

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

How do you know you need a cooler that enormous?

 

[stutaeng]

What tranmission are we talking about here?

 

[Frank Enstein]

I recommend this cooler.

B&M 80212 B&M Analog Transmission Temperature Gauges | Summit Racing

Free Shipping - B&M Analog Transmission Temperature Gauges with qualifying orders of $109. Shop Gauges at Summit Racing.

www.summitracing.com

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.

 

[Frank Enstein]

As long as the transmission temp stays 160F to 200F it doesn't matter how you get there.

Colder than that can lead to moisture in the fluid (strawberry milkshake) that will destroy the clutches.

Every 20F degrees above 200F cuts the transmission life in half. Above 380F you won't get around the block.

If it's super cold like in Schurkey land putting the cooler first in line can work, but I would recommend the inline thermostat in that case.

Like this one.

https://www.summitracing.com/parts/der-13011

 

[Schurkey]

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.

Every 20F degrees above 200F cuts the transmission life in half. Above 380F you won't get around the block.

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.

If it's super cold like in Schurkey land putting the cooler first in line can work, but I would recommend the inline thermostat in that case.

Like this one.

https://www.summitracing.com/parts/der-13011

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.

 

[sweetk30]

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 .