Transmission high temperature in 6L80

[SLC2]

I have 2018 Suburban with 6L80 Trans. Recently started seeing temperatures as high as 270F with normal driving on highway or even around town after an hour of driving. I am wondering if this is a Trans temperature sensor problem. The trans cooler lines into and out of the radiator are at 150F. So my thinking is one of the following. 1) Thermal bypass valve malfunction, 2) Clogged or partially clogged trans cooler lines, 3) malfunction in the report of the temperature.  I intend to replace with the  newer  85585333 GM bypass valve.  But I am wondering if anyone else has experienced this situation. I can't find anything on the internet about temps for this trans this high. 

[rav3]

You might try this 1st.

1. Disconnect both transmission lines from the trans thermostat. 

2. With compressed air, blow out the transmission cooler lines, blowing thru the return line with a jug container on the outlet line, and see if any debris is in the jug. I used a clear plastic drink bottle to catch the fluid & then looked to see if it caught any debris. 

 

Note from AI.....On your 2017 Chevrolet Silverado 1500 5.3L with the 6L80E, the transmission fluid flow is:
Upper cooler line at the transmission = Hot fluid OUT to the radiator/transmission cooler.
Lower cooler line at the transmission = Cooled fluid RETURN back into the transmission.
At the radiator/auxiliary cooler, the fluid typically flows:
Out of the transmission through the upper line.
Through the radiator heat exchanger.
Through the auxiliary cooler (if equipped with the factory towing package).
Back to the transmission through the lower return line..

 

Then with the thermostat removed, I installed a thermometer defeat (bypass) that bought off Amazon. This one has no moving parts.

 

Edited Saturday at 09:16 PM by rav3

[rav3]

[mikeyk101]

This seems like an even better solution than doing the pill flip. I like it!

Edited Saturday at 09:21 PM by mikeyk101

[rav3]

4 minutes ago, mikeyk101 said:

This seems like an even better solution than doing the pill flip. I like it!

Yes, I thought so too. Cheaper & no moving parts. Actually makes it like the old 4L80E transmission. It's what I replaced my pill flip with

[diyer2]

Miles? Has it been serviced?

[MikeBMW]

I've referred to this many times over the years and I've had zero issues after the installation.
Also, it helped a friend of mine resolve transmission issues he was having with his 2018 GMC Sierra.
Chevrolet TSB 21-NA-199.pdf