Before spending a bunch of $$ chasing a problem, step back and analyze the situation...

Think about how the cooling system works. It uses pressure to raise the boiling point of the water, and more effective heat transfer. This has to be regulated, however, or you will blow components out. The system pressure is regulated by the radiator cap. When greater than 16?PSI is achieved, it will release excess pressure into your coolant overflow tank, to avoid blowing hoses, cores, etc.

If your headgasket or head were pushing excess pressure into the cooling system, it would vent out into the overflow, either blowing the top off of it (seen it before), or overfilling it, spilling all the coolant out of the overflow tube.

Start by pressure testing the cooling system. When 16PSI is surpassed, see if the coolant is being pushed into the overflow. If not, replace the cap.

Heck, forget the test. If your cap is more than a year old, it can't hurt to replace it anyway. <img src="/forums/images/graemlins/cheers.gif" alt="" />

"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living." - John F. Kennedy

Proud owner of an 88 Montero (with a blown engine).