View Full Version : Can you blow the head gasket driving without pressurized coolant?

01-14-10, 10:02 PM
Hi all, I didn't realize, but i had a guy put a new thermostat in today and i stopped to get gas and realized coolant was leaking out. I filled it up and noticed the pressure cap didn't hiss. The temp gauge stayed normal. It idled for about 20 minutes like this, could that damage the head gasket? :banghead:

01-15-10, 03:56 AM
you're being paranoid.... that wouldn't damage anything.

You may want to pressure test the cap though. The cap keeps the system under pressure to raise the boiling point of the coolant. With a failing cap it will let coolant expand more and boil over, which basically means you'll end up low on coolant. Being low on coolant can lead to overheating the engine (if you don't fill it back up when the message goes up on the dash) which can be bad news for headgaskets.

01-15-10, 08:39 AM
The coolant reservoir should be half full with the engine cold. Do NOT fill it to anywhere near the top, cold or hot.

You probably have a 16# pressure cap - if the system will not pressurize so the hoses get hard when hot, you need a new $8 pressure cap.

Where was the coolant leaking out of ???

................no, the head gasket(s) won't blow but the engine will boil over at a lower temp with no coolant pressure: at 16psi coolant boils at 265 degrees; at atmospheric pressure it boils at 218 degrees.