Thank you for the information! I have an 06 Suburban 2500 with the 8.1L with a 4:10 gear ratio. It tows my 6000 lbs camper with no problem of course. My trans temp always hung around 195 also but on some steep hills it would also climb up in temp or on long hauls on a hot day. At a stop light one day not long ago at 95 degree weather the engine temp climbed a bit but cooled down once I got driving again. I suspected it was the clutch in the cooling fan going bad so I replaced it with AC Delco replacement part and had no problems since. It also seemed to be helping with my trans temp too as I’ve been on three or four more trips this summer without the trans temp climbing.

 

Yeah, you have to keep your eyes on the transmission fluid temp when towing.
You have a 2500 and 4.10 gear and that's very nice to have my friend.
I'm putting a tru cool 40k axiliary cooler on my 2001 to replace the small factory one.
Hope to get the 2001 at least to 300k miles and I'll be happy.

 

I made a diagram of the GM factory transmission fluid thermostat in bypass and cooling mode.
Let me know if you have any comments to add.

 

will this fir 2010 suburban?

 

Di ako sigurado.

I think it started in 2014 when they started installing them.
Look under by the transmission on the driver side,

 

sayang . hhehehehe

 

I just wanted to share what I did to prep my 2018 Suburban for towing my camper.

Under normal driving (no towing) my transmission temperature stays around 195F - 198F. When I first tried towing my 5000 lb camper, the temperature went up to 210F on a slight incline after a 2-hr drive. So I stopped towing with my 2018 Suburban and just used my 2001 Suburban with 285k miles that came with the heavy duty trailering package equipped with external cooler (KNP) and GT4 (3.73 gear). The 2001 did very well on a 5 hour trip to Pensacola, FL this past week.

After researching, I found out that the 2018 Suburban with the 6L80E has a transmission cooler thermal bypass valve from the factory. It does not allow fluid flow to the cooling lines to the transmission cooler located on top of the hvac condenser until the fluid temp reaches 190F. So basically, the fluid is recirculated back to the transmission without passing thru the cooler in the front. Good design to get the fluid up to operating temp fast. When the fluid temp reaches 190F, it opens up the line to the cooler and supposedly will drop the transmission temp down. But I think the bypass opening is proportional to the fluid temp. So who knows when it opens up fully. (maybe 230F ?)

I searched the internet for 6L90E transmission products to get around the thermal bypass. I found a few youtube videos.
1. One recommended to pull out the bypass valve (GM# 1351136) tap the hole and install a plug to the bypass hole.
This keeps the line to the cooler always open. The drawback is it will take a while to get the fluid to operating temp.
2. Mishimoto low temp thermal bypass valve. Included with the cooler kit. Very expensive at $400.
3. I found a product STL010 Sure Cool transmission system upgrade that is meant to replace the thermostat inside the bypass valve. Reasonable at $43.

I went with Option# 3.
So far so good after the test drive.
Normal driving, my transmission temperature stayed at 158F - 160F. (see attached pic)
Towing transmission temps still remains to be seen later.

Have you towed any heavy loads since doing the surecool fix? What did you temps stay at then?

Any downfalls to installing?

 

I towed my 5k lb travel trailer from Georgia to the Grand canyon sometime last year. TFT stayed at 160F cruising along I-10 to Texas then to New Mexico. Highest TFT was at 180F.
I sold the camper trailer and bought a class B diesel. I only got 10-11 mpg on the 2018 1500 suburban.
Now I'm getting 20-21 mpg.

If you want to run your 6L80e cooler, don't get the sure cool. Get the new 158F lower temp thermal bypass valve from GM .
The original one is 190F. Too hot before it opens to trans cooler.

 

I just bought a toy hauler and towing it in 100F this past weekend, it was pushing up to 225. Ridiculous. Always wondered why get so hot, now that looking at all this information, it shouldnt have ever been close to it.

 

One recommended to pull out the bypass valve (GM# 1351136) tap the hole and install a plug to the bypass hole.
This keeps the line to the cooler always open. The drawback is it will take a while to get the fluid to operating temp.

Apparently. Pulled it off and someone tapped and plugged it. No spring. No pill plunger. We live in a colder climate, so now I am wondering what to do. Not sure if the kit would still seal to go to cooling mode if I removed if plug and installed the Superior Solutions kit. Thinking I will just reinstall for now and decide what to do (if anything) in the fall.

 

A better upgrade is replacing the factory 190°F thermal bypass valve, TBV, with the new available lower temp 158°F TBV instead of modifying the 190°F thermostat.

TBV Part Number 86774933, stamped with “70”

 

I have the old connections that don't match up with new TBV, and would have to run all new lines. I bought some connectors that I hoped would adapt but it doesn't look like it will work. Still trying to figure out the right solution before desert (Grand Canyon) and Colorado mountain towing our 32' travel trailer.

Probably easiest to leave the plug for summer and the trip so it is always cooling. Certainly not ideal for sub-zero winters.

Did I read somewhere that SUVs don't have tran dipsticks but trucks do? Our Yukon XL does, but we replaced with rebuilt. And it looks like the transmission shop way overfilled fluid. Far above the mark cold or warm. Afraid that overfilled it won't circulate the way designed. Going to suck some out from fill tube and see how it does. Hoping to have time to change fluid anyway with 35k on replacement transmission.

 

I have the old connections that don't match up with new TBV, and would have to run all new lines. I bought some connectors that I hoped would adapt but it doesn't look like it will work. Still trying to figure out the right solution before desert (Grand Canyon) and Colorado mountain towing our 32' travel trailer. Probably easiest to leave the plug for summer and the trip so it is always cooling. Certainly not ideal for sub-zero winters.

I've been looking at doing this as well with the GM updated part. Apparently with the older style that has the different connections, you can take the inner parts out of the old one and replace them with the parts from the new one. Here's a link for a video on how to do it

 

I bought and installed the TBV Part Number 86774933 thermostat and still running 200º !!