Transmission temperature

Ahmad Alfilchawi · January 5, 2020

Hello guy I got 2015 Chevy Silverado 4x4 5.3L single cab short bed. I have done few mods which is (afe intake- jets throttle body - tune). usually in the weekend me and my friends go for off roading trips, and I am facing a trouble with the transmission temperature it could reach to 221F usually what I do, i open the hood and the AC for couple of minutes till it goes down. What I want to ask that I just have to delete the transmission thermostat or install transmission cooler, or the last option is to do both of them.

Grumpy Bear · January 6, 2020

7 hours ago, Ahmad Alfilchawi said:

Hello guy I got 2015 Chevy Silverado 4x4 5.3L single cab short bed. I have done few mods which is (afe intake- jets throttle body - tune). usually in the weekend me and my friends go for off roading trips, and I am facing a trouble with the transmission temperature it could reach to 221F usually what I do, i open the hood and the AC for couple of minutes till it goes down. What I want to ask that I just have to delete the transmission thermostat or install transmission cooler, or the last option is to do both of them.

Depends on your speed and your water thermostat/fan settings. The delete is easy, quick and cheap. Do that first and test. Then revaluate. I did the delete and at highway speeds it takes a really hot day to break 165F. Sitting dead in traffic like at an accident it can get about 210 F. That said a cooler without a thermostatic fan won't help much at crawling speeds. (off road)

Edited January 6, 2020 by Grumpy Bear

UofAZCats · January 6, 2020

8 minutes ago, Grumpy Bear said:

Depends on your speed and your water thermostat/fan settings. The delete is easy, quick and cheap. Do that first and test. Then revaluate. I did the delete and at highway speeds it takes a really hot day to break 165F. Sitting dead in traffic like at an accident it can get about 210 F. That said a cooler without a thermostatic fan won't help much at crawling speeds. (off road)

Not that familiar with the intricacies of transmissions, but if you can delete the transmission thermostat then why did GM include it? What is its purpose? I would think its job is to keep the the tranny cool but that seems to be the opposite of what it does. Just trying to learn about this so any info is appreciated.

davester · January 6, 2020

It's likely to get the transmission up to it's operating temperature faster.

rbrjr1 · January 6, 2020

everything that heats up and cools down has an optimal operating temperature (even our own bodies)..

Tstats are used to prevent crazy swings in operating temperature or to maintain a specific range.

Grumpy Bear · January 6, 2020

12 hours ago, UofAZCats said:

Not that familiar with the intricacies of transmissions, but if you can delete the transmission thermostat then why did GM include it? What is its purpose? I would think its job is to keep the the tranny cool but that seems to be the opposite of what it does. Just trying to learn about this so any info is appreciated.

10 hours ago, davester said:

It's likely to get the transmission up to it's operating temperature faster.

1 hour ago, rbrjr1 said:

everything that heats up and cools down has an optimal operating temperature (even our own bodies)..

Tstats are used to prevent crazy swings in operating temperature or to maintain a specific range.

1.) Why indeed! Because viscosity is temperature dependent. Because viscosity is a measurement of a fluids internal resistance to flow. Because lower resistance means less parasitic fuel waste. Because the manufactures are driven by law to seek additional gains in fuel efficiency. That's the why.

2.) What they are suppose to do is MAINTAIN a target temperature. IN this case about 192 F. The transmissions cooler, which is in the radiator as it has been for a very long time without a thermostat; actually functions as a heater at first as the water temperature rises more quickly than the transmission fluid temperature. Once fluid temperature rises (load driven) higher than the water temperature then is becomes a cooler. Hold that thought.

The OEM thermostat does NOT have a minimum flow bypass and because is does not the transmission actually takes LONGER to come to heat than if it had no thermostat at all. Now put that thought with one your holding and you will see the flaw in the idea of a more rapid heat up.

3.) Unlike the human body whose operation indeed is enhanced by finite temperature control of a few degrees the transmission has a much wider tolerance. MUCH wider. Functionally it is happy as a clam between a bit over 100F fluid temperature. Actually colder but the computer sets some limits on fuel and spark that are fluid temperature dependent. It continues happy until it gets too warm to afford the device adequate protection. Varnish starts to form around 220 F. Yes even with PAO lubricants

Most major transmission parts suppliers and builders will tell you to keep the fluid under 180 F for longest life. GM's goals for your gearbox do not include you. They are CAFE driven.

Chew of this. The transmission thermostat hasn't a minimum flow bypass. Has a set temperature of 192 F. The cooler is in the radiator HOT SIDE tank if you have a V8 and that thermostat is 207 F. :wtf:

GENE SEWELL · July 1, 2022

On 1/5/2020 at 1:11 PM, Ahmad Alfilchawi said:

Hello guy I got 2015 Chevy Silverado 4x4 5.3L single cab short bed. I have done few mods which is (afe intake- jets throttle body - tune). usually in the weekend me and my friends go for off roading trips, and I am facing a trouble with the transmission temperature it could reach to 221F usually what I do, i open the hood and the AC for couple of minutes till it goes down. What I want to ask that I just have to delete the transmission thermostat or install transmission cooler, or the last option is to do both of them.

global transmission part#STL010 .REPLACES THE GUTS OF THE TRANSMISSION BY PASSvalve - COOLER . 2014 and up works awsome there is a you tube video you can watch . .around 50.00 us .better than the original thermostat .

CajunFries · July 2, 2022

Do the thermostat flip mod. You can look up the video on YT. It’s free and it’s just like a delete. If you’re not happy with that, get a Trucool 40K…. I never had the trans temp go above 160-165…. (I have my trucool for sale btw)

pokismoki · July 2, 2022

depending on your abilities, you might want to install a pipe plug between the crossover point on the hot and cold side of the cooler adapter, , i think its better than the flip trick because of less fluid blockage created by the thermostat when flipped, either way works. pipe plug is $12 for plug and a tap, flip trick is free, or aftermarket delete kit whith the added anti-drain check ball is about $65

Grumpy Bear · July 2, 2022

This is my latest data finally completed recently

Gandalf · July 26, 2022

GM quietly admitted their mistake with the original automatic transmission by-pass valve (thermostat) in 2014-2018 gas trucks. A while back, they replaced the part we all have from the factory, and replaced it with a part that looks identical, but that opens to send fluid to the cooler at a much lower temperature (158F, I think).

I did try the “flip the pill” method, which was dead easy, but in my haste to complete the job, I neglected to press the c-clip into its channel fully. Ended up with a few litres of ATF coating my garage floor! In my fury at myself for missing such a simple thing, I got more angry at GM. So, I googled a bit and found the new part (86774933), which my local dealer had in stock.

For the cost of a $100 (in Canada, everything costs more) part and minor effort to install, the truck now operates at safe temperatures all the time. Before, the ATF heated to around 195-210 just driving to work (half hour on hilly roads). With the new by-pass, it never gets above 150-155, even during a recent 8-hour drive through mountain passes here in northern BC, fully loaded and - because of 35 inch tires - constantly gearing down early on even small hills, not to mention the many 1-6 km long hills. It only reached 166 a few times, after sitting while I got gas or food.

This is the only transmission mod I have, so those lower temperatures are all with just the factory in-radiator transmission cooler, and while driving at the hottest time of year - averaged 90-100 F. I thought I might require a good aftermarket cooler, and was about to order the Mishimoto one, but it’s overkill for now.

As any ATF fluid temp/tranny longevity chart shows, fluid this cool prolongs the life of the transmission by app. 40,000 miles. So far, the best thing I’ve done to the truck (2015 AT new to me in March this year).

Edited July 26, 2022 by Gandalf

Grumpy Bear · July 26, 2022

What does 70C mean?

70 C (158F)

158 F is the 'fully open' temperature.

148 F is the 'throttling' temperature.

138 F is the 'cracking temperature.

[larger graph in post above].

IF it won't stay in the 'throttling' range then more cooler is required to keep it there.

Not required if it stays under 180 F in your world of operation; just a physical fact.

Gandalf · July 26, 2022

7 hours ago, Grumpy Bear said:

What does 70C mean?

70 C (158F)

158 F is the 'fully open' temperature.

148 F is the 'throttling' temperature.

138 F is the 'cracking temperature.

[larger graph in post above].

IF it won't stay in the 'throttling' range then more cooler is required to keep it there.

Not required if it stays under 180 F in your world of operation; just a physical fact.

Thanks for this. As I alluded in my comment, I am a bit concerned about winter. Even though where I live is mild, we still get below-freezing temperatures fairly regularly.

Embarrassingly, the automatic transmission is the one I know the least about - even though my father was an AT specialist (for Ford, but . . . ). He was so busy when I was growing up, taking on side jobs rebuilding transmissions, he didn’t have time to teach much. So, I don’t know how - or even if - ATF can be too cool for the good of the trans.

For now, I’m just happy with the results of just replacing a single part - I bored my family last week while on the road trip: I kept pointing at the DIC transmission temperature, amazed that it was 65C, not the usual 88-92C.

I had a good transmission cooler as my next job for the truck, but I’m thinking I’ll hold off until winter, just to be sure the fluid does not remain too cool on sub-zero days. I also plan to drive up North in January, to an area that stays under zero all winter, often down into -30C or lower. So, I will definitely have a good idea how to proceed with the trans cooler or not.

I am also adding the B&M Hi-Tek deep trans pan this week, which adds 3 quarts to the fluid capacity. I’m not completely sold on that - I think their claims of the efficacy of added fluid volume is valid for their diff covers, but I’m not sure simply adding more ATF to the sumo will lead to much more cooling. But, I bought it anyway, for the drain plug alone.

This is a very helpful forum, and I have been reading all of your and others’ solid advice since March, when I got the truck. Thank you!

Grumpy Bear · July 27, 2022

4 hours ago, Gandalf said:

I am a bit concerned about winter.

Don't be. Automatics have been radiator cooled since the early 1960's without thermostats. I mentioned in another post this thermostat does not have minimum flow bypass so it isn't even on the cooler until about 140 F. Driving them puts enough heat into it to keep it warm enough for everywhere but the artic circle.

Gandalf · July 27, 2022

Thanks again! (Hmmm . . . Now to decide what to spend the money on instead. This could become addictive - I’m glad I’ve switched to GM after 30 years innFords!)