Transmission thermostat delete results

leathermaneod · February 9, 2024

Hi all,

I know this topic has been beaten to death, but I haven’t seen much about results. I have some results to share. My truck is a double cab, 4x4, custom with 145,000 miles. I switched to the updated GM stat around 138,000 and was mostly happy. Towing my 7000 lb camper at highway speeds in 90° heat it would be around 160°-170°. At low speeds it would climb quickly to as high as 198° ish. Once back up to speed it would start to cool down again. In southeastern PA winter, it runs around 145° not towing and fully warmed up. I hadn’t planned to change anything until a mechanic I talked to mentioned that these stats sometimes jam up and I might not realize it till too late. I had seen the tap and plug mod before so I decided to try this. I had read that the fluid would be quickly warmed by the coolant it’s close to in radiator, but would then be kept cooler than normal by the unrestricted flow. Well now I think it runs a little cold, but I’m interested to hear everyone’s thoughts. It was 49° today and it took forever to warm up. It is definitely not being warmed by proximity to the coolant and no I do not have any additional coolers or even max tow package. Once warmed up, low speed in town, the highest I saw was 127°. Cruising at 40 mph on back roads, it drops as low as 111°. Slow down and it warms a little, but cools back off with airflow. I haven’t done any highway driving or towing yet, but so far I’m thinking of going back to the updated GM stat and just keep this one with me in case of emergency. I always monitor my trans temp while towing anyway. I’m curious, what are all of your thoughts on these results? I’d like to be able to keep it below 180° at all times, but I’m not sure that will work even with this setup and I’m not sure if I’ll cause any issues with it being too cold in the winter. So far, this is not what I expected at all.

CamGTP · February 9, 2024

Put it this way, prior to 2014 they never had transmission thermostats in the first place.

Running cooler temps was never a problem for those transmission. I deleted the thermostat on my 2016 years ago, it struggles to get over 100-110 degrees in during the winters if I'm not beating on it around town. It may hit 150 but then cool right back down. This is exactly how my 2012 behaved and it never came with a factory thermostat.

mikeyk101 · February 9, 2024

@CamGTP is correct and these didn't normally come with external trans fluid coolers unless added aftermarket. My only issue and why I didn't completely delete the thermostat is that I found that at the cooler trans temps in the winter, the shifting is a bit sluggish and harsh. Once the fluid warmed up, shifting was greatly improved. But like you, I was always concerned that it was running hotter than it needed to be. I swapped out the 90c thermostat for the 70c one as soon as I found out about it. I am way happier with the trans fluid temps now and feel they are where they should be. 145⁰ to 154⁰ or so on steady runs not towing. Stop and go city traffic (also not towing) and it might go high 170⁰ or even into the 180⁰ range. Once I get out of that and back on steady runs, it cools down quickly.

Looks like you have a 2018. FYI, the transmission fluid when external to trans flows through the condenser and not the radiator. The 2014 and 2015 IIRC, had the trans cooling lines flowing through the radiator. Because yours doesn't flow though the radiator, engine coolant will not have much of an effect on helping trans fluid warm up in cooler temperatures. And the original transmission fluid thermostat was a 194⁰ thermostat so it definitely ran warmer to begin with. As long as fluid is in good shape, getting up to 198⁰ on the new trans thermostat is definitely not something I would have been worried about.

Where I got worried was towing up a long (and I do mean long by several miles) 8 percent grade in the Big Horn Mtns where not only the trans temp went high but so did the engine oil and coolant (260⁰ ish) to the point that I had to stop and let it idle to cool down. Luckily that is a rare occurrence and never gets that high.

mikeyk101 · February 9, 2024

Sorry, my last paragraph might be misleading. I was explaining the temps I was seeing with the original 90c trans thermostat before switching. I have not had a chance to test this again as those mountains are roughly 1100 miles away so it may be a while before I can get back out there...

rlcole321 · February 12, 2024

Yes back in the days, trans was "Warmed" up by the coolant. I was an auto tech for 20 years (back a while, OBDII had only been out a few years when I changed careers) and I always thought trans coolers were in the Rad. (so when I got my 2018 'Rado, I didn't understand why GM used a Trans tstat), I didn't think about it until I did a DOD delete on my truck and took it apart that the trans cooler was in the condenser, then the trans tstat made sense! So unless your a performance wild man, your trans need to warm up just like your engine, so running a trans tstat makes sense and I think 190 is too high.

newdude · February 12, 2024

On 2/8/2024 at 7:49 PM, leathermaneod said:

Hi all,

I know this topic has been beaten to death, but I haven’t seen much about results. I have some results to share. My truck is a double cab, 4x4, custom with 145,000 miles. I switched to the updated GM stat around 138,000 and was mostly happy. Towing my 7000 lb camper at highway speeds in 90° heat it would be around 160°-170°. At low speeds it would climb quickly to as high as 198° ish. Once back up to speed it would start to cool down again. In southeastern PA winter, it runs around 145° not towing and fully warmed up. I hadn’t planned to change anything until a mechanic I talked to mentioned that these stats sometimes jam up and I might not realize it till too late. I had seen the tap and plug mod before so I decided to try this. I had read that the fluid would be quickly warmed by the coolant it’s close to in radiator, but would then be kept cooler than normal by the unrestricted flow. Well now I think it runs a little cold, but I’m interested to hear everyone’s thoughts. It was 49° today and it took forever to warm up. It is definitely not being warmed by proximity to the coolant and no I do not have any additional coolers or even max tow package. Once warmed up, low speed in town, the highest I saw was 127°. Cruising at 40 mph on back roads, it drops as low as 111°. Slow down and it warms a little, but cools back off with airflow. I haven’t done any highway driving or towing yet, but so far I’m thinking of going back to the updated GM stat and just keep this one with me in case of emergency. I always monitor my trans temp while towing anyway. I’m curious, what are all of your thoughts on these results? I’d like to be able to keep it below 180° at all times, but I’m not sure that will work even with this setup and I’m not sure if I’ll cause any issues with it being too cold in the winter. So far, this is not what I expected at all.

Normal operation for a full delete. IMO, I'd put the GM updated temp thermostat back on at least during the winter months.