Fellas-I put a pressure test guage on my radiator and brought it up to operating temperatures, however the pressure increased while I revved the engine ( I know this is normal). At operating temp and with the guage on it read 8PSI. At what pressure should I be concerned the head gasket is lossing the battle....over 20 PSI?

 

The head gasket is designed to handle at least engine cylinder pressures, with a margin of safety beyond that. Don't have the FSM in front of me, but I thought the max spec for cylinder compression was something like 175 or 195 psi on the 2.7L and 3.4L motors.

If your cooling system got anywhere near there you'd be blowing up hoses and splitting radiator tanks long before the HG would fail.

 

Do you suspect a HG leak? Is that why you are worried about rad. pressure? If so, its not a matter of amount of pressure, its a matter of whether the rad holds pressure over time.

HG leak test would be to pressurize the radiator and then let it sit for an hour or two and then check to make sure it held pressure.

 

If you're worried about a HG, leave the pressure tester on overnight with the plugs out. You'll see coolant in the cylinder(s) in the morning if the HG is leaking.

 

Or run tube from your overflow tube to a jug of water and see if compression gases are bubbling in the bottle of water. This will tell you if compression gases are escaping into cooling system.