Temperature Question: Transmission Thermostat Upgrades (Flipping the pill)

Ubiquity · March 17, 2023

My truck: Finally named Ubiquity 4.3 2015 2wd

I am considering the other options as well. But for now my question is about flipping the pill. I'm having trouble understanding how the transmission temperature will drop below the temperature of the engine coolant, when its temp. has been at 220F since mile 1? How can I expect it to drop the transmission temp. to 160F (as others state) if it passes through the radiator? For that matter, how does it now stay below the coolant temp in its current factory state?

Maybe someone will correct or confirm the follow theory: The temperature reading for the coolant is on the engine, near the thermostat; whereas the coolant directly in the radiator is significantly cooler.

Edited March 17, 2023 by 2015regcablongbed

AZ_SS · March 17, 2023

I bought the bypass kit and it works great. I believe the external cooler is after the radiator.

AZ_SS · March 17, 2023

The engine coolant sensor is measuring engine entering coolant temp, which is the same as the leaving radiator temp.

JerryS. · March 18, 2023

The transmission uses its internal pump to pump transmission fluid through transmission lines through an external transmission cooler and back to the transmission. I don't know if your particular model uses a tranny cooler that is built into the radiator or a separate cooler. My 2015 GMC Sierra 1500 5.3L 4WD came with the separate tranny cooler. In the old days, transmissions were constantly cooled using this setup. In recent years, Chevy/GMC installed a transmission thermostat in these trucks to control the temperature of the transmission fluid inside the tranny. If I remember correctly, the factory thermostat is a 190 degree unit. The thermostat opens at 190 which means, depending on what you're doing with the truck, the tranny will tend to run hotter than that temperature setpoint. Many suspect the thermostat causes the transmission to run too hot for its own good and is detrimental over time. I purchased a transmission thermostat bypass kit and installed it. Easy install for my truck (30 minutes with no mess). My truck can display the transmission temperature on its information center display. The tranny temperature previously ran well over 190 degrees during the summer. It now runs around 160- 170 degrees with the bypass kit. I heard a rumor that Chevy/GMC now offers an optional 150 degree transmission thermostat, but never bothered to confirm since I'm satisfied with the bypass kit.

Edited March 18, 2023 by JerryS.

Ubiquity · March 18, 2023

My 2015 4.3L has lines that go to the right side of the radiator tank. So how would a ~ 210F water temperature lower the transmission from its now 185F+ temperature to ~ 165F?

I'm just having my coffee now, so I need more time to think about this.

Thanks for all your replies.

Edited March 20, 2023 by 2015regcablongbed
misstated temperature: 210 instead of 220

Grumpy Bear · March 18, 2023

15 hours ago, 2015regcablongbed said:

My truck: Finally named Ubiquity 4.3 2015 2wd

I am considering the other options as well. But for now my question is about flipping the pill. I'm having trouble understanding how the transmission temperature will drop below the temperature of the engine coolant, when its temp. has been at 220F since mile 1? How can I expect it to drop the transmission temp. to 160F (as others state) if it passes through the radiator? For that matter, how does it now stay below the coolant temp in its current factory state?

Maybe someone will correct or confirm the follow theory: The temperature reading for the coolant is on the engine, near the thermostat; whereas the coolant directly in the radiator is significantly cooler.

For you this is how this works. I know as I have the same truck, different color.

The 2015 4.3 transmission cooler is in the COLD side tank of the radiator. Your engine coolant temperature is taken on the outlet of the motor. Your water thermostat is 207 F and the radiator will pull 25 F-35 F out of the water's temperature depending on season, load and speed (of air through the radiator). Mid 170's with the stock thermostat.

These other 160 F and lower temperatures are from V8 setups where they have, depending on year and RPO either both radiator and air-to-air cooler OR just the air-to-air cooler.

OR as in my case I have installed a 170 F radiator thermostat. Below are my results. Orange is pill flip and 170 F thermostat. Blue pill flip and 180 F thermostat and the last, yellow is the new 70 C trans TBV and 170 F water thermostat. Mine to ran 220F plus in midsummer with the stock water and transmission thermostats.

CajunFries · March 18, 2023

22 minutes ago, 2015regcablongbed said:

My 2015 4.3L has lines that go to the right side of the radiator tank. So how would a ~ 220F water temperature lower the transmission from its now 185F+ temperature to ~ 165F?

I'm just having my coffee now, so I need more time to think about this.

Thanks for all your replies.

The trans fluid is not getting “cooled” by engine’s coolant. It looks like it but nope. If you look carefully, the radiator and the trans cooler is together in one piece but there is a separation between the two. So the trans fluid is being air cooled. Yes some heat will transfer between the two since it’s somewhat connected. So by having a lower temp thermostat or being bypass, that will dictate where you trans temp will usually be.

Ubiquity · March 18, 2023

Hello CajunFries: I thought you might find the video interesting.

36 minutes ago, CajunFries said:

The trans fluid is not getting “cooled” by engine’s coolant. It looks like it but nope. If you look carefully, the radiator and the trans cooler is together in one piece but there is a separation between the two. So the trans fluid is being air cooled. Yes some heat will transfer between the two since it’s somewhat connected. So by having a lower temp thermostat or being bypass, that will dictate where you trans temp will usually be.

Ubiquity · March 18, 2023

Hello Grumpy Bear:

"The 2015 4.3 transmission cooler is in the COLD side tank of the radiator. Your engine coolant temperature is taken on the outlet of the motor. Your water thermostat is 207 F and the radiator will pull 25 F-35 F out of the water's temperature depending on season, load and speed (of air through the radiator). Mid 170's with the stock thermostat. "

That's what I thought. Thanks for chasing away the endless detritus one inevitably finds within the shadows of time.

And yes, I had come across your detailed temp graph before. That's always reassuring to have someone who takes the time to put in that level of information.

Additionally, for those not lucky enough to have the 4.3L like we do: my 2015 has the plate style retainer on the Transmission bypass valve. I can't remember where, but apparently some 2015's might have the clip retainers instead.

Grumpy Bear · March 18, 2023

8 hours ago, 2015regcablongbed said:

Thanks for chasing away the endless detritus one inevitably finds within the shadows of time.

I can't remember where, but apparently some 2015's might have the clip retainers instead.

You are welcome. Pepper is as much a hobby as a truck. Mine has the plate like yours as well. 2014 was clipped. Do some early 2015's have clips? :dunno: That would be a @newdude question. He's really active here and I learn allot from him.

Interesting use of the word "detritus"

newdude · March 20, 2023

On 3/18/2023 at 7:55 PM, Grumpy Bear said:

You are welcome. Pepper is as much a hobby as a truck. Mine has the plate like yours as well. 2014 was clipped. Do some early 2015's have clips? That would be a @newdude question. He's really active here and I learn allot from him.

Interesting use of the word "detritus"

I think early 15s do? They changed somewhere in that early 2015 build phase.

Then the other change on V8s was the lines flow differently. 14-early 16s the transmission goes to the radiator then to the condenser combi cooler then the transmission. Late 16-19LD they bypassed the radiator and its standalone transmission to the condenser then back. When the pill flip/sure cool are done on these they run real cold come winter time. 15-20F mine wouldn't get past 100F and shifted laggy due to the low temp. I ended up installing the GM revised TBV and winter performance improved.

Edited March 20, 2023 by newdude

Grumpy Bear · March 20, 2023

3 hours ago, newdude said:

I think early 15s do? They changed somewhere in that early 2015 build phase.

Pepper's build date is March 8th, 2015. That's what, about halfway through the production year?

newdude · March 20, 2023

2 minutes ago, Grumpy Bear said:

Pepper's build date is March 8th, 2015. That's what, about halfway through the production year?

Yea probably just over. Switch over to 2016 MY would have happened likely July to September time frame 2015.

Ubiquity · March 20, 2023

Thanks Newdude

I'm looking at a May build 2015 for Ubiquity.

Buckwild27 · March 22, 2023

I can confirm the 150° updated transmission thermostat I had them swap it before I bought my 2014 a month ago. On a 60° day cruising down the interstate it runs at 158° in town can get up to 170° in lots of stop and go traffic.