[GStage1]

The reason for the head gasket statement....I have found several engines with the same problem.....removed about 1" of fluid below the radiator filler hole, ran the engine without the cap on and watched as bubbles percolated in the fluid....the engine was pumping air/fuel mixture into the coolant......engines never consumed fluid.....due to the way the head gasket was letting the air enter the coolant. Replaced both head gaskets and no more air bubbles or pressure.

On a normal engine, you should leave a little room for thermal fluid expansion so you don't spill fluid. Once the engine/coolant returns to normal outdoor temperature...there should not be any pressure since the heat is gone.