Wet Compression Test
squirt a little bit of motor oil into each spark plug hole and crank the engine over to distribute the oil evenly.
must be done on a warm engine and helps to identify whether compression leakage in the dry test is past the valves or the piston rings.
if any compression readings increased significantly on the cylinders that were low on the dry test, leakage is likely past the piston rings.
If the compression readings did not increase or increased only slightly in the wet test, the leakage is likely past the valves.