Hi All-

Just finished my first compression test on my '88 740 Turbo. I feared the head gasket was blown at 150K as two consecutive checks of the oil showed light brown froth on the dipstick. After dismantling the coolant system, draining oil and coolant, and removing the distributor, I started to doubt my pat diagnosis of blown gasket. As per the instructions of several at this board, I picked up a compression tester and followed instructions as best I could.

I removed fuel pump fuses, ignition on, coil disconnected. Used remote starter to crank motor. Held throttle wide open with vice-grips.

As I didn't replace anything but the filter and the oil, I couldn't run the car up to operating temperature for the test. Maybe this was a bad assumption, but I thought regardless of temp I would be able to diagnose cylinder to cylinder leaks, etc. I figure I might have caused unnecessary wear, but anyway...

#1 cylinder tested far to low. 60-90 psi. 2,3,4 all in the 150 psi range.

Retested #1 cylinder, thinking maybe lack of oil circulation might cause false low. Not the case, retest was the same as first, 60-70 psi.

Put some oil into the spark plug hole, maybe a little too much, but not a quart.
This retest resulted in really high reading, first test at 180psi, second at 150 psi. Then the weirdness begins-

The release valve on the gauge sprayed a little brown foam. I removed the valve, placed a rag over the nozzle of the tester hose, and tried clearing the cylinder that way, just to be sure. finally got down to a vapor, so reattached gauge and twice read 150psi.

SO, bad rings on #1 or bad testing? Did I maybe screw up the compression tester? Any input welcome-

Dylan