[PWRHGRY]

Does anyone know the indicators of a blown head gasket? I know the obvious, but during a compression test, how much drop in pressure will a cylinder with a blown head gasket read? I understand these cars can blow head gaskets with no indication in engine coolant.

 

[CallMeMud]

Bubbling in your overflow. Gasket material in your oil pan. 10% variance on a compression check. Milkshake in your oil!! Pissing coolant to the outside. Sudden large spike in coolant temperature. White smoke out the exhaust with coolant smell. Probably a couple more I can't recall.

 

[ULYCYC]

Your vacuum gauge at idle will be erratic. When I blow a head gasket it's usually a big event eek!

 

[Orlando_87GN]

I have found a regular compression check to be inconclusive in determining head gasket health. For example I did a compression test on my number 1 cylinder once and had 150psi of compression. Funny how water was shooting out of the bleed valve on the gauge though. A leak down test revealed 90% loss of pressure though and lot's of hissing in the oil pan

I think the reason for this is eventhough the headgasket is blown, the piston is moving pretty fast inside the bore when cranking the motor and you would need a huge gaping hole see it on a compression test... A gasket blown into the waterjacket especially will not show up, because the cooling system is in effect acting as a closed system for the escaped air.

 

[1badTTA]

ULYCYC:
Your vacuum gauge at idle will be erratic. When I blow a head gasket it's usually a big event eek!

Nearly all of my headgaskets blew bad enough I could slide a credit card into the cylinder with the head still bolted down. Therefore a compression test easily tells me which cylinder is bad.

If your HG isn't that bad, do a leakdown test and when you find the worste cylinder, squirt some oil in it to make sure it isnt the rings. That will tell you it is either the HG or a valve, either way the head is coming off.

 

[ULYCYC]

As Mike said sometimes a compression test won't show a problem. I've seen some just move the fire ring enough to just cause high boost popping and pass a compression test,No water tank surge or oil blow out.

 

[1badTTA]

ULYCYC:
As Mike said sometimes a compression test won't show a problem. I've seen some just move the fire ring enough to just cause high boost popping and pass a compression test,No water tank surge or oil blow out.

This is true, but if you take it out and stand on it for a full pass, you won't be wondering if it is a blown headgasket anymore. (make sure you can coast into your garage after the run) headbang cheers

 

[ULYCYC]

Actually it held up fine up to 22lbs of boost then started popping. Didn't change until a few weeks later. I have a friend now running 11.30's with the same problem. He hopes it will last for the E-Town Buick meet.