So I need some advice here. I’ve been a long time lurker, first post. A little bit of info, I have a 2015 Tahoe LT 4x4 with the 6l80, I bought it with a bad converter and it was unable to move, the trans was shot. Long story short, I’ve rebuilt my 6L80 myself following nicks transmissions on YouTube. I’m fairly confident in the job that I did. Once I put it in and start driving, the temp goes up, but never comes down. So then I thought well I’ll put a thermostat bypass in it, it didn’t change anything, then I put the big 40k cooler on it, still no change. Maybe it takes it longer to heat up, but still doesn’t regulate at what a normal temperature should be. The upgrades i did were sonnax billet piston, transgo valve body shift kit, borg warner high energy frictions, superior solutions bypass, the cooler, I’m sure I’m forgetting more stuff. If anyone can shed an any insight, im all ears. Thanks!
Overheating 6L80e
- Thread starter Ryat242
- Start date
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swathdiver
Full Access Member
exactly what "temps" are you seeing?
Did you replace the TEHCM? if so, did you program the new TEHCM to the vehicle...How hot is the temp getting? Temps shouldn't be above 200-215 F daily/normal street driving....
I do recall one of my builds got real hot very fast and the tech doing the install stopped right away and turned it around...The fix had something to do with the tune; some parameters that required adjustment...Sorry, I don't have the details but whatever the tuner adjusted, it worked and temps went down to 160-170isih and stayed there...
Okay. So I’m very glad you added that second part. Today when I tested it it got to like 190F fairly quickly. I then turned off and had the laptop with me and kind of went back through the tune that I had loaded, I didn’t really see any issues with it but I reloaded it to the truck on the side of the road (I was desperate lol) after I did that I started it up and it dropped to the 160-170ish range and when going through stop and go traffic it creeps up to 185ish but that’s the hottest it got after that. Now my question is, with a thermostat bypass and the big cooler I have installed, is 160-170F about what should be expected? I kind of thought it would be lower, but it’s definitely fluctuating now, which is something it wasn’t doing at first. **I also wanted to add that the weather today was 55 F
Now going back to the first question, no I didn’t replace the TEHCM, I bench tested it and it all looked good. So I just thought id roll the dice on it, I did rebuild the little screens on the TEHCM though.
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So I never really saw a really high temp, I guess I was more concerned with the amount of time it took too get “warm,” if it was idling, it would slowly increase but if you drove it, it would shoot to 190F within 5 minutes or so, even when the temps outside were mid 30s. So I knew something wasn’t right, I also noticed that it never fluctuated, just kept increasing 2 degrees at a time rather steadily, no matter the speed or gear it was in. Once it jumped up to 190, I would turn around. I never saw it go over 215 id say.
@NickTransmissions i do want to give you a huge thank you for everything that you do on YouTube, you were a huge help! I have a hydraulic background, and have built several engines in the past but never a transmission, to say I was intimidated would be an understatement. Your videos made it make sense and gave me a great starting point to work from. I’ve recommended to all my buddies to watch your channel and give it a try themselves before taking theirs to a shop. I like knowing exactly what was replaced in a rebuild and a lot of the shops in my area I’ve talked to are very vague on what they actually replace. So a huge thank you!!
160-170 is ideal but Dex 6 can handle 200-215ish no problem so if you're consistently seeing 185ish and it stays that way throughout the summer months then it's fine. The 6L80 in my GMC Sierra doesn't get hotter than 175-180 which is perfect for most automatic transmissions. Keep an eye on the TEHCM, IMS and speed sensors if you didn't replace them...The IMS doesn't go bad very often but the other two do fail more frequently once mileage on them gets north of 200k...
You're welcome and thank you for watching my videos - appreciate the support and recs ! Congrats on your first rebuild.
With our thermostat deleted 15 suburban we just took a 2 hour road trip this past weekend with temps in the 20's and 30's transmission never went above 125. All highway driving. In the summer on a road trip, again all highway, it usually is around 140-148. It's the wife's so I only drive it on our road trips. City driving I don't have a clue since where we live and go I wouldn't call it "city" driving.
that’s about what I was expecting, somewhere in the 140 ballpark. Im hoping it’s alright, I don’t want to cause any damage. But the truck drives flawlessly now, I mean shifts out good, no tieups or flare outs at all. Today on the drive into town about 30 miles of 55mph the it sat around 145-155. So maybe I’m overreacting fingers crossed.
So to go into a little deeper, I rebuilt the trans around 3 months ago, drove it and it was doing this issue then too. So that’s when I did the bypass and cooler, when it didn’t change I got worried I had installed a seal incorrectly or perhaps had knicked something when doing the install. So I bought another gasket/seal kit and tore it back open. Of course all the frictions and steels were in fine shape. I inspected everything and found nothing broken or installed incorrectly. Not knowing what the issue was, I just resealed it back up and here we are now. My question is, if something were bypassing causing heat is there anything in the valve body that could cause it? I made sure all the check balls were where they were supposed to be and torqued all the bolts to specs so I was confident in it, but now knowing all the seals are fine and nothings broken, its got me wondering. When I closed it back up this last time I didn’t touch the valvebody because I knew everything was correct. Have you ever seen that or heard of a valve body causing an issue like this? I have 2 spare core transmissions with good valvebodies in them, would it be worth it to rebuild one of those and stab it in?
Question: When you plumbed in the new cooler did you keep the oil-to-water cooler in the radiator end tank in the loop, or did you just go straight to the 40K? I'm asking because you'll see much higher temps without that radiator end tank in the loop. I know this first-hand.
I bypassed the radiator all together. Going straight from the trans to the cooler and back. Is that what you mean?
That's the problem. Plumb it through the radiator then out to the aux cooler .
Uh
What’s the thinking on this? Trust me I believe you guys. And I’ll try anything, is the fluid moving too fast to actually cool it? Or is the radiator cooler that efficient? I noticed yesterday that the faster you go, the quicker it builds heat. About a 20 minute interstate ride and the temps didn’t start to drop until i got off and went to a slower speed. And it cooled the best when it was sitting at a stop? Is this due to rpm and the thus making the fluid go faster through the aux cooler?
When I installed the cooler I couldn’t for the life of me find a video or thread taking about the best way to hook it up so I winged it. My thinking was that the trucks radiator sat at 210 once warm and I wanted the fluid to be cooler than that. Haha. Scientific I know.
You're way over thinking this...Fluid is a much more efficient heat exchanger than air so by eliminating the fluid's travel through the radiator's internal transmission cooler, you've cut your cooling efficiency by at least 50% or so....
73Vetteman
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Curious if slipping torque converter or clutch packs are creating excess heat.
Did you run the adaptives to adjust clutch pack apply pressure after your rebuild?
Have you disabled DOD? There is more converter slip when DOD is active. Also try driving in tow/haul mode to see if that helps.
Did you run the adaptives to adjust clutch pack apply pressure after your rebuild?
Have you disabled DOD? There is more converter slip when DOD is active. Also try driving in tow/haul mode to see if that helps.
In his case, neither - it's the lack of or inefficient heat exchange due to bypassing the internal radiator trans cooler. If the clutch in the converter and/or those in the trans were slipping, they would def be adding to the excessive temp condition...
73Vetteman
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Others are correct to plumb cooler lines into radiator cooler first, then into auxiliary cooler. Reason for this is that radiator temperature is never hotter than engine temperature and usually much cooler. After being cooled in radiator your auxiliary cooler will further reduce oil the temperature.
Most agree that using the newly revised thermostat is better than the bypass. The revised thermostat with GM part number ending in 933 opens at a lower temperature than the original. The thermostat only brings oil up to its operating temperature of 70 degrees C. After that it free flows oil to cooler. It won’t provide more or less cooling during hot spells. Especially important in cooler climates. The updated thermostat is about $40 on eBay or Amazon. The GM part number ends in 933.
Most agree that using the newly revised thermostat is better than the bypass. The revised thermostat with GM part number ending in 933 opens at a lower temperature than the original. The thermostat only brings oil up to its operating temperature of 70 degrees C. After that it free flows oil to cooler. It won’t provide more or less cooling during hot spells. Especially important in cooler climates. The updated thermostat is about $40 on eBay or Amazon. The GM part number ends in 933.
