Transmission temperature

Kevin Sayer · July 29, 2023

Does anyone know if there is a difference in the V8 vs. The V6 transmission cooling system? I have a v6 and installed the tru-cool thermostat and still saw temps reach 200°f. I recently swapped that out with the "updated" 158° one from GM and that seems to be not much different from the tru-cool one. Am i missing something? Thanks

newdude · July 29, 2023

1 hour ago, Kevin Sayer said:

Does anyone know if there is a difference in the V8 vs. The V6 transmission cooling system? I have a v6 and installed the tru-cool thermostat and still saw temps reach 200°f. I recently swapped that out with the "updated" 158° one from GM and that seems to be not much different from the tru-cool one. Am i missing something? Thanks

V6 doesn't have an auxiliary cooler. Its transmission to the cooler inside the radiator and then back.

V8s have an aux cooler out at the front, its the top 1/4 of the AC condenser. Also, 14-earl6 16 V8 the lines go transmission to radiator, radiator to aux and then aux to transmission, where late 16-19 don't go through the radiator at all, so the early trucks run warmer like the V6 do and the later trucks run cooler than both. My 19 old body with the Surecool on a hot day would barely crack 140F, and with the GM updated TBV installed it would hit like 160F max on a hot day.

Edited July 29, 2023 by newdude

Grumpy Bear · July 29, 2023

2 hours ago, Kevin Sayer said:

Does anyone know if there is a difference in the V8 vs. The V6 transmission cooling system? I have a v6 and installed the tru-cool thermostat and still saw temps reach 200°f. I recently swapped that out with the "updated" 158° one from GM and that seems to be not much different from the tru-cool one. Am i missing something? Thanks

1 hour ago, newdude said:

V6 doesn't have an auxiliary cooler. Its transmission to the cooler inside the radiator and then back.

The water temperature of the cold side radiator tank is the limit. With a factory 207 F water thermostat throttling at perhaps 210 F the cold side temperature will depend on the ambient air temperature and air flow. Air flow is typically at its peak between 50 and 55 mph. (Second chart below). On a hot day let's say you get a 30 degree drop hot side to cold. If you are starting at 210 F the cold tank is 180 F.

The cold side and the ATF flow in counter current directions. This means the ATF can never get as cold as the cold-water side. This is the 'approach temperature'. Typically, and roughly 20 degrees so now you ATF can get cooler than 200 F.

Won't matter what temperature the ATF thermostat is set at if that temperature is below this number. Wide open is wide open.

Okay so you have two options. Colder water, which you get with a colder water thermostat and/or a larger radiator OR a secondary air to air ancillary cooler in series and after the cold tank OR a really large air to air and remove the cold side from the loop.

That last option has a small problem. It blocks air flow from both the radiator and the AC condenser. Fans run more and AC efficiency suffers.

Katech has a 174 F water thermostat that is a five-minute drop fit into the factory housing. That alone will cool the ATF about 30 degrees on a 85-degree day. You will still run out of cooling on hotter days, driving faster than 55 or towing/hauling at the limit and worse the more of these you stack. It is, after all, a load based system.

This is the temperatures my V6 runs at 55 mph with a 170 F Reisch Racing thermostat and the 158 F TBV. Not a drop in but for your edification. You see where it runs out of throttling range of the thermal bypass valve (TBV).

If you drive faster or slower than the target window the temperatures will rise (below chart) requiring yet again additional cooler.

I'm going to take advantage of a small radiator leak and replace it with the slightly larger GM-21902 NHT unit. Should increase the temperature drop over the radiator which should be of benefit on hotter days. My aim is to keep the TBV throttling on the hottest days I may drive in. That may mean I add a secondary cooler as well. But one step and check at a time.

Edited July 29, 2023 by Grumpy Bear