GM 6L80 Transmission Information Thread

[shrutefarms12]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

 

[donjetman]

you need to install an aftermarket trans cooler setup like many folks here have done.

 

[NickTransmissions]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

I've shut off all inbound *** - there's absolutely no reason for me to provide tech support via PM as it's duplicative, redundant and defeats the purpose of having an open forum (not to mention a total waste of my time). So you posted this in the right place.

You must flip the pill or install a thermal bypass valve delete kit and add a large aftermarket transmission cooler to your set up. The updated T-stat still restricts fluid flow based on temp and ultimately results in the transmission running hotter than it should. Those stupid TBVs are pointless unless you live in Canada or Alaska.

 

[Geotrash]

@NickTransmissions

Sorry in advance if this is not the place to post this. I tried sending a PM but system would not allow me to send it. I have a 2018 tahoe that has had its 6l80e replaced by my local chevy dealer @90k miles. They installed the updated thermostat on the transmission that supposedly keeps trans fluid cooler. Ever since the new transmission got installed, anytime I am towing anything moderately heavy like my boat (6k pounds) the transmission temps slowly build until it hits 280 degrees and goes into limp mode. I have brought it back to dealer many times and they replaced the TEHCM module but that still has not solved the issue. Any ideas what could be going on? Dealer basically said to blow it up again for them to do anything else. Seems they don't believe me even though I have many pictures. I am approaching the end of the warranty period and want to get this figured out before it expires. Any insight would be greatly appreciated.

Thanks! -Nick

One of the stupid shop tricks I've read here several times is that when they replace the transmission after a failure, many of them simply bypass the radiator's end tank oil-to-water heat exchanger rather than replace the radiator. They do this ostensibly to protect the new transmission from any debris still trapped in the exchanger. But as I've learned first-hand, doing this will result in seriously elevated fluid temperatures when towing. My guess is that this is what they did in your case.

Your truck should have BOTH the radiator end tank exchanger AND an external transmission cooler plumbed IN SERIES with each other.

Trace the cooler lines from the transmission to the coolers and back and let us know what you find. If I'm right, then the solution is to replace the radiator with a Denso (OEM manufacturer). If the external cooler is still in the circuit then plumb it in DOWNSTREAM from the radiator's heat exchanger. If the external cooler is NOT plumbed in currently, then replace it with a new one and plumb it in downstream from the radiator. I say this last part because if they bypassed it then it's likely still filled with debris.

Net/Net: you want BOTH a clean radiator end tank heat exchanger AND a clean external fluid cooler plumbed in series. The heat exchanger takes a big cut of heat out of the fluid before it hits the external cooler. Trust me on this. I have done the experiments myself.