Search results

Sounds like some type of blockage in the return lines. There may be some type of check valve that opens with a certain amount of pressure.

Looking at the diagram there seems to be a small filter in there. Could be clogged.

I don't see why you couldn't carefully bleed the pressure down. If the spare tire check valve is the same maybe you can swap it in place of the cab one.

There are check valves in the manifold.

Flush the system. The overflow tank is aluminum if its starting to corrode you dont want that circulating in the cooling system. If you flush and get water in there then you should be able to use a pressure tester to see where the leak is coming out. Or just pressurize the overflow tube with air.