Originally Posted by vstech

there are several different ways to test compression.
as long as it's noted which way it was tested, the results are valid.
a cold engine will have lower compression numbers than a warm oil soaked engine will.
a quick way to see if the motor has excellent compression on a to buy trip is to insist the motor not be started prior to your arrival, and by hand VERIFY the motor is stone cold.
then, unplug the glow plug harness, and crank the motor. if it starts quickly, it's got good compression. if it will NOT start, (unless it's below 30°F outside) the motor has some compression issues!
a cold compression test (done with ALL injectors out, and the IP wired to shut off fuel) will reveal unequal piston compression.
not a valid test to get compression totals though. need warm engine for that.