K2XX Trans cooling concerns

Mwalabama · April 12, 2023

Folks with the 159’ trans thermostat, over long drives does your trans temp still climb well over the 160 mark? I drove my 17 Sierra 220 miles today and by the end of the drive it had reached 180’ in 80 degree ambient temps. I would like to think the cooling system is efficient enough to keep it lower..?.. The condenser/trans cooler was replaced a while back, but this issue happened before that. Once I parked and let it idle, it dropped to 165 in 15 minutes. I’m not concerned right now, but I will be when it gets too 100’f out (Alabama weather, yay) and I’m pulling my boat to the beach or my other truck to and from the track on the flatbed. Do y’all think I’m missing something here and I have some issue? Or is this the standard and I need to just add an external cooler?

When I first swapped the 159 thermostat( when the new trans was put in) the temps stayed at 145 all the time, but it hasn’t been that way in quite a while.

I even pill flipped it and all that did was make it take forever to warm up but to the same effect.

Full system fluid change was done about 1k miles ago with oem filter and ac delco dex6 fluid. Trans has around 47k on it. Truck has about 127k on it.

Do y’all think I’m missing something here and I have some issue? Partially plugged line? Or is this the standard and I need to just add an external cooler?

Any help would be appreciated at this point..

Edited April 12, 2023 by Mwalabama

MikeBMW · April 13, 2023

I had the dealer install the TSB transmission fix. A friend of mine did the same on his GMC and has yet to have another issue.

MC-10207911-9999.pdf

Grumpy Bear · April 13, 2023

On 4/11/2023 at 10:32 PM, Mwalabama said:

Folks with the 159’ trans thermostat, over long drives does your trans temp still climb well over the 160 mark? I drove my 17 Sierra 220 miles today and by the end of the drive it had reached 180’ in 80 degree ambient temps. I would like to think the cooling system is efficient enough to keep it lower..?.. The condenser/trans cooler was replaced a while back, but this issue happened before that. Once I parked and let it idle, it dropped to 165 in 15 minutes. I’m not concerned right now, but I will be when it gets too 100’f out (Alabama weather, yay) and I’m pulling my boat to the beach or my other truck to and from the track on the flatbed. Do y’all think I’m missing something here and I have some issue? Or is this the standard and I need to just add an external cooler?

When I first swapped the 159 thermostat( when the new trans was put in) the temps stayed at 145 all the time, but it hasn’t been that way in quite a while.

I even pill flipped it and all that did was make it take forever to warm up but to the same effect.

Full system fluid change was done about 1k miles ago with oem filter and ac delco dex6 fluid. Trans has around 47k on it. Truck has about 127k on it.

Do y’all think I’m missing something here and I have some issue? Partially plugged line? Or is this the standard and I need to just add an external cooler?

Any help would be appreciated at this point..

Air temperature. That's the difference. It runs hotter in hotter weather cause the air that cools it is hotter. If you want the ATF cooler then you have two choices. Additional cooler or less load. As you want to tow....... Yea, more cooler.

dmoe0826 · May 8, 2023

On 4/12/2023 at 9:42 PM, MikeBMW said:

I had the dealer install the TSB transmission fix. A friend of mine did the same on his GMC and has yet to have another issue.

MC-10207911-9999.pdf 68.43 kB · 15 downloads

I'm assuming this would not be a covered fix outside of the warranty period?

Grumpy Bear · June 26, 2023

On 4/12/2023 at 9:42 PM, MikeBMW said:

I had the dealer install the TSB transmission fix. A friend of mine did the same on his GMC and has yet to have another issue.

MC-10207911-9999.pdf 68.43 kB · 32 downloads

Seems my 2015 is not on that list. I did it anyway.

mikeyk101 · June 27, 2023

I just got done last week towing my toy hauler with my 2016 5.3 with 6L80 trans. I did the updated thermostat last year.

Recently I noticed that my trans temps were up a bit but checking further, my coolant temps and oil temps were much higher than they should have been (over 200⁰ F) even in milder temperatures. I finally figured out that the Motorad 194⁰ thermostat I installed earlier this year to fix my defective OEM 207⁰ thermostat must have failed and been getting stuck shut. I ended up taking out the Motorad thermostat and then installing a lower temp 194⁰ GM thermostat. That seemed to help tremendously. When not towing, my coolant and oil temps pretty much stayed below 200⁰. And the trans temps stay cooler like in the 150-160⁰ range unless I really get on the accelerator. Then it may rise a bit more but drops back down.

Now when towing the toy hauler on last trip that is close to 6000lbs loaded, the coolant and oil temps did hover in upper 190's to mid 200's and the trans temp would climb to 180 or just a bit higher but stayed in reasonable territory. I'm happy when towing that the trans temp never hit 200⁰. This was in lower 90's ambient temperatures. Overall much better than last year. And this was also running AC the whole time and AC was nice and cool.

You may want to find out how your coolant and oil temps are and using the dash coolant gauge is not very accurate. If those temps are running in the 200's or higher (210-220 range) normally, you might want to look at the coolant thermostat and install a lower temp OEM one. Coolant temps and oil temps usually stay pretty close and by keeping coolant temp down, oil temp stays lower and that in turn should help with lower transmission fluid temperature as well.

mikeyk101 · June 27, 2023

Just to add, even though your trans temperature does seem to be going a bit high, it's still under where you would be if you still had the original transmission fluid thermostat installed.

mikeyk101 · June 27, 2023

And I just noticed OP hasn't been back since late May. Hopefully he comes back to read the responses but I'm not holding my breath...

Mwalabama · June 27, 2023

Hi all,

To follow up, I flushed all the lines, even bypassed the thermostat completely to see if any difference was made. Nope, none..

After a trip where the trans temp got up to 210 pulling my 17’ Key west center console boat (guessing 3500lbs loaded) in 83’ ambient temps on mostly level ground, I decided to add an additional aftermarket trans cooler in line after the factory cooler.

yesterday I towed the same boat on the same drive, 97’ ambient temps with 95% humidity, temps stayed south of 170 even in standstill traffic and rolling 80 on the highway on 35s.

with no trailer it stays floating around the 140-150 degree area even in 90+ temps.

Grumpy Bear · June 27, 2023

6 minutes ago, Mwalabama said:

Hi all,

To follow up, I flushed all the lines, even bypassed the thermostat completely to see if any difference was made. Nope, none..

After a trip where the trans temp got up to 210 pulling my 17’ Key west center console boat (guessing 3500lbs loaded) in 83’ ambient temps on mostly level ground, I decided to add an additional aftermarket trans cooler in line after the factory cooler.

yesterday I towed the same boat on the same drive, 97’ ambient temps with 95% humidity, temps stayed south of 170 even in standstill traffic and rolling 80 on the highway on 35s.

with no trailer it stays floating around the 140-150 degree area even in 90+ temps.

Can you tell us what cooler, brand, part number you used?

Mwalabama · June 27, 2023

I ended up using a Hayden 679 and made some custom brackets out of steel. My truck has the active shutters so I fit it behind the radiator bracket in front of the radiator.