Oil in coolant

[Roy and Tracy Boling]

My truck has oil in the coolant reservoir. 2020 Silverado 2500HD Z71 WT with 6.6L gas engine, 9,300 miles. I am still waiting for the diagnosis from the dealership. Has anyone experienced this issue in a new truck? Update, the transmission cooler in the radiator failed, replacing radiator and hoses, everything that is saturated in transmission fluid.

Edited December 21, 2020 by Roy and Tracy Boling
Update

[Rob Mugs]

Will likely see more results here:

https://www.gm-trucks.com/forums/forum/245-20192020-silverado-sierra-troubleshooting/

 

[Roy and Tracy Boling]

It is transmission fluid, not engine oil, in the coolant. They have been in touch with tech support and are working down their list. They called tech support since it is a first for that shop.

[CamGTP]

A guess would be the transmission cooler built into the radiator has cracked.

[Ray Pickle]

I second that diagnosis

[Stand By]

Hoping they're inspecting the transmission as well? Guessing after the vehicle is shut off, while at operating temp, pressurized coolant could be forced into the no longer pressurized transmission line (heat exchanger)?