K2XX Trans Cooler Thermostat Thoughts and Opinions

YYC-SIERRA · January 31, 2022

Sweet, thanks for the info on the kateck t-stat, i just looked it up. Definitely something i'll plan to install when we're back home.

CadillacLuke24 · April 9, 2022

The original 192 Trans thermostat on my 8L90E did no favors to the internal electronics, so I did the pill flip. It worked very well, in colder temps (less than 30F) the trans wouldn't get past 120. Maybe a slight fuel economy drop, but nothing major if longevity was the payoff.

When I saw the 6L90E thermostat I figured it was time for experimentation. The guts for the 6L90E and the 8L90E are the same size, so I just swapped internals across.

Very happy with the results, trans warms up to 145 and tends to hang there unless I'm in town, at that point the warmest I've seen is 163. The nice thing is the cooler is 'stepped', so that when you reach the mid 140s it opens a little bit, and it will open a little bit more as it warms, until it hits 158 where it's full open. At least it seems like that, cause the temp increase noticeably slows when it reaches the 140s.

Possibly a slight fuel economy increase, if the weather cooperates I could tell better. Shifting is more responsive for sure (think quicker, not harsher) and as a result more fun to drive. I think GM should promote this on the 8L90E too.

mjs1012 · April 19, 2022

I swapped from the factory 190 t stat to the sure-cool last summer, and while it was great in the warmer months, in the winter it struggled to get to 100-110F, especially on the highway. It would shift pretty rough for a few minutes and based on this, I'm planning on putting in the newer thermostat to help improve cold weather performance.

On another note, does anyone have the part numbers for the cooler line o rings? I lost one when I did the sure-cool swap and used a random o ring that fit but would like to get new ones just to have in case.

Grumpy Bear · April 19, 2022

Updated Chart with the new TBV

I posted this chart on page one before the installation of the new TBV. You might note that the legend says 138 F instead of 158 F which means that I chose to use the 'cracking' temperature of the valve instead of its fully open temperature like every other thermostat maker on the planet.

Remember that Pepper, as the 4.3 swaps tanks in the radiator to use as oil and ATF coolers vs the V8 models and in addition does not, as a pre 2016 or any NHT, have the secondary or aux cooler mounted in the top half of the AC condenser. In addition I have fitted a colder water thermostat than factory which as a radiator cold side tank cooled transmission has some effect on the absolute temperatures. (Currently the colder of the two shown, orange bubbles).

Lastly note the speed this chart is constructed at. In the top of the sweet spot of the cooling range 25 Meters per second or 56 mph being optimal. (engineering for fin fan exchangers). Trans will run warmer much above or below this as was shown in the graph below. While this graph was constructed from data at 30 F it holds true at any temperature.

All this to say, "Your results may vary" WILL VARY. However directionally they will be the same.

What I had thought is this new TBV would put a floor on the temperature and I don't know why I thought that in retrospect. Large aluminum case is a huge heat sink AND Pepper is fitted with an oversized finned 8 quart PLM ATF pan. Still it removed the radiators cooling from the system and allowed for a higher low air temperature ATF operating point. This did help with low temp fuel efficiency and moved through the 68 F to 104 F area where some have noticed shift quality differences.

Later this week we are to see our first near 80F day of the year and I hope to capture a result for that point which I expect to fall right around 153 F, between the two previous points. Looks like where the trend line is pointing.

You guys need to make note that these charts are at constant operating speeds on the Interstate for several hours to allow everything to normalize. City driving WILL raise the operating temperatures as will high speed and towing situations. Even a 20 mph head wind vs a 20 mph tail wind will effect things. Think DIRECTIONAL results not duplication of this trucks performance.

Once I have enough data the plan is to install a small secondary cooler to "Cut the head off the snake" to keep her under 160 F no matter what conditions prevail.

customboss · April 20, 2022

On 1/25/2022 at 2:28 PM, Black02Silverado said:

@newdude, great post and a ton of information. Thanks for posting this. Everyone that has a 2014 and up with the 6l80 and 6l90 would greatly benefit to changing out their thermostat. As newdude stated GM even realized the issue.

I feel that one would benefit from changing out the thermostat and switching over to a quality synthetic ATF like AMSOIL. My good fortune with all my transmissions has been the fact that I switched all my vehicles over to AMSOIL ATF pretty much right away. My 2002 Silverado I had the dealer do a full exchange at 5k miles on the truck. I did a pan drop and fluid change at 75k miles. That post is here. I then switched over to AMSOIL's ATL fluid when they came out with it back in 2006. I pulled the cooler line and did a fluid exchange. This was around 100k miles on the truck.

I switched over the 2016 Suburban at 10k miles and just did the 2019 Silverado with the 10sp at 25k. Why so late on it? Well I was hoping someone would come out with a Youtube on how to do it yourself. Well it never happened due to the fact that, to my knowledge, the fill plug is on top of the transmission and you really can't get to it. The dealer fills it back through the cooler lines and then checks the fluid from the side level port at a certain operating temperature. I've had the AMSOIL ATL in it now for over 1,000 miles and it shifts great. To me it has a crisper shift if that makes sense.

Then time got away from me and before I knew it I hit 200k and I did a pan drop and fluid change. I sent a sample off and the results came back good. In that 100k mile time frame I started towing on occasion, a 10'x20' box trailer for Ainsley's Angels and the weight of the trailer is just under 4,500lbs.

Again, installing the lower temp thermostat and a quality synthetic fluid will keep the transmission running smooth for a long time.

One thing I forgot to mention is I change out the transmission fluid every 50k miles in all my vehicles. My 2014 Cruze diesel's transmission runs at 220°F to 225°F according the the Scan Gauge II I have hooked up to it. Way to hot but it is what it is.

Since it looks like your 2016 Suburban version ate the TQ converter from the fluid pump failing I am with POKISMOKI its a seal, bushing, and shaft issue. There is NO WAY that Amsoil ATL can't handle the temps and the fact you changed it out twice in a failure at 81,000 miles points to sealing failing which over heats the pump and converter, maybe the valve body. I am betting that when the oil analysis comes back the back end clutch packs and planetary's are fine. I bet the amount of trash in the filter is low too. Once again its GM execution of their engineering that fails.

teagan · April 21, 2022

What are normal operating temps for the 8l90? On roadtrips it will hover between maybe 180-190ish. I read the topic concerning the 6spd so was wondering if the same problems are encountered on the 8spd. I have 6.2 manufactured in May of '15. I also live in a cold climate where winter mornings are below 30F routinely. Sound like the the "new" gm thermostat is the way to go??

Grumpy Bear · April 21, 2022

2 hours ago, teagan said:

What are normal operating temps for the 8l90? On roadtrips it will hover between maybe 180-190ish. I read the topic concerning the 6spd so was wondering if the same problems are encountered on the 8spd. I have 6.2 manufactured in May of '15. I also live in a cold climate where winter mornings are below 30F routinely. Sound like the the "new" gm thermostat is the way to go??

It isn't a question of what is normal. It's a question of what's required, period. That answer has not changed in about 70 years. Something under 160 F. Anything after that is poly-ticks, horse feathers and corporate strategy.

teagan · April 21, 2022

11 hours ago, Grumpy Bear said:

It isn't a question of what is normal. It's a question of what's required, period. That answer has not changed in about 70 years. Something under 160 F. Anything after that is poly-ticks, horse feathers and corporate strategy.

Can you recommend what the best solution is? I know horse feathers are a nice aftermarket part and all...

Grumpy Bear · April 21, 2022

2 hours ago, teagan said:

Can you recommend what the best solution is? I know horse feathers are a nice aftermarket part and all...

I know the "guts' of the new TBV slip right into the 8L and 10L TBV's. It may be the whole valve is interchangeable.

You have a 15 which is pre shutter. Is yours NHT equipped? If so your done. If not do the valve first then watch the temps during the hot months to see what if anything you need for extra cooling.

newdude · April 21, 2022

17 hours ago, teagan said:

What are normal operating temps for the 8l90? On roadtrips it will hover between maybe 180-190ish. I read the topic concerning the 6spd so was wondering if the same problems are encountered on the 8spd. I have 6.2 manufactured in May of '15. I also live in a cold climate where winter mornings are below 30F routinely. Sound like the the "new" gm thermostat is the way to go??

1 hour ago, Grumpy Bear said:

I know the "guts' of the new TBV slip right into the 8L and 10L TBV's. It may be the whole valve is interchangeable.

You have a 15 which is pre shutter. Is yours NHT equipped? If so your done. If not do the valve first then watch the temps during the hot months to see what if anything you need for extra cooling.

Yes, you can swap the guts from the new 6 speed TBV with lower temp thermostat into existing 6, 8 and 10 speeds.

teagan · April 22, 2022

What is NHT?

Grumpy Bear · April 22, 2022

3 minutes ago, teagan said:

What is NHT?

RPO code for NHT PERFORMANCE PACKAGE ENHANCED TOWING (page 142 of included link.)

https://rparts-sites.s3.amazonaws.com/dec399b0838336997484042ed2af1004/design/rpoCodes.pdf

rav3 · April 23, 2022

14 hours ago, teagan said:

What is NHT?

NHT - MAX TRAILERING PACKAGE: * 9.76 REAR AXLE * TRAILER BRAKE CONTROLLER * ENHANCED COOLING RADIATOR * REVISED SHOCK TUNING * HEAVIER DUTY REAR SPRINGS AND INCREASED RGAWR

This is the RPO code call out for my 2017 silverado with MAX towing package. (5.3l & 6 speed trans)

teagan · April 23, 2022

You mentioned a '15 as pre-shudder; I have read a lot of threads on here about that. I feel lucky to have a year where this is not a problem. Do we know what the general cause of the shudder is (in a nutshell)? On a entirely different note, is a "diablew" tune worth it? I have the Diablo i3 Platinum I believe and I reprogrammed some of the shift parameters in 1st-2nd gear. When it shifts from 1st-2nd, the rpm's jump, (clutch?) any thoughts?

JimCost2014 · April 23, 2022

28 minutes ago, teagan said:

You mentioned a '15 as pre-shudder; I have read a lot of threads on here about that. I feel lucky to have a year where this is not a problem. Do we know what the general cause of the shudder is (in a nutshell)? On a entirely different note, is a "diablew" tune worth it? I have the Diablo i3 Platinum I believe and I reprogrammed some of the shift parameters in 1st-2nd gear. When it shifts from 1st-2nd, the rpm's jump, (clutch?) any thoughts?

Bad fluid from the factory in the transmission, or the TC going bad.

Had the TSB done on my 18 with the new Mobil One Blue Label, and it has a made a big difference. I did not experience the shudder until 44000 miles. Have put over 4000 miles on the new fluid, no more shudder, and strange shifts are a lot less frequent. Biggest thing I have noticed, is it will hold a lower gear at slower speeds, so does not lug quite as bad as before.