: Compression Test for Head Gasket Leak

05-01-04, 02:50 PM
After many trials I've finally diagnosed my 97 Deville N* with a blown head gasket. Cylinder 3 leaks a lot and the adjacent cylinders, 1 & 5, are leaking a little.

Here's how I did the test. Remove the radiator cap and fill the overflow tank completely full. I had a Prestone coolant funnel in place. It allowed the coolant to surge a little without spilling and I could watch the coolant level raise and lower in the funnel. Idle the engine to warm it up and keep the coolant tank full. Remove all the spark plugs like you would do with a regular compression test. Insert the compression gauge and crank the engine over 10-15 times. Watch the coolant in the overflow tank while the engine is cranking. The leaking cylinder will force coolant out of the system with each compression stroke. You'll see the coolant rise in the funnel or in my case, overflow all over the place.

You could do this without a compression gauge by using a single sparkplug.