Trans runs hot at times.

I was told there is some kind of check valve that can stick in the cooling system and cause problems.


Is this true and if so where is it?

I have a 92 w250 with a A518

 

Sounds like it might have something to do with the engine coolant tranmission fluid heat exchanger. It's under your turbo. Mine was disconnected before I bought my truck. It's supposed to help the trans warm up and cool at the same time IIRC. There might be a thermostat or something in that too maybe?