I recently purchased a 1974 240D. 170k miles documented. New short block at 70k after original owner damanged the oil pan and lost oil pressure.

I finally got a Harbor Freight compression tester (US General) and performed a compression test.

Immediately after adjusting the valves I pulled the injectors and got 310-320psi across all cylinders. Smug and happy with that, I didn't bother with a wet test.

For the heck of it, I borrowed another gauge (same Harbor Freight) and repeated the test.

This time around I got only 270-290 psi at each cylinder and 320ish wet.

The car isn't using any oil (well, not in the 300 miles since I changed it) and fires up on the first or second turn after being glowed. On warm days I don't even have to glow. As a matter of fact, it almost tried to light off with all fuel injectors out after I added two teaspoons of oil for the wet test.

That being said, there is some smoke coming out of the oil fill at idle and also some oil leaking around the crankcase vent hose on the intake side. The lid will hover, but won't go flying across the engine compartment. It also idles rough until it's warmed up but then is smooth as butter.

Given the mileage, I thought that the 325 figure would be about right. But the symptoms listed above make me think the lower numbers are more accurate.

Which ones do I go with?

In any event, there seems to be a huge variance in US General Compression Gauges due to quality control issues. Some people out there might be fretting unnecessarily while others could be overly confident.