Welcome to the forum.


The loss of heat, simulataneously with the rise in temperature certainly points to air in the cooling system. Now, whether the air is simply there from the last flush and fill, or whether combustion gases are charging the cooling system, is the question.

Some questions/tests:

1) Has the cooling system recently been opened/flushed?

2) How often to you add coolant to the expansion tank to maintain level? After driving for some distance, is the level in the tank down about 8 oz. or so, the next morning?

3) After allowing the vehicle to sit overnight, after running it hard, open the hood and sqeeze the upper radiator hose. See if you can squeeze two fingers together. Make a mental note of the stiffness of the upper hose. Then remove the cap on the expansion tank and observe if any pressure releases. Now squeeze the upper hose, again, and observe any difference in firmness from the original test.

Your answers to these questions will assist us in solving the problem.