98 V70 T5, 232k, daily driver, blows a little oil on start up which I presume is valve seals but otherwise runs great.

So I parked the car, and the next day it wouldn't start. It had that free spinning sound like no compression (timing belt?), not the normal cranking sound.

I checked the belt and it's good. Did a compression test and got -
40, 60, 40, 170, 40.

That was two days ago. Today I did another compression test, then squirted some oil in the cylinders and did it again. I got -

Dry - 60, 80, 60, 35, 75
Wet - 90, 120, 75, 45, 140

Put the plugs back in, cranked and cranked and it eventually fired. Drove around the block to warm it up, and tested it again. I got -

185, 180, 185, 185, 185

Now I'm confused. Any thoughts appreciated

 

Wet compression tests should always be more than dry, but those numbers don't make any sense. How did you have 170 on cylinder 4 initially, then 35 dry and then 45 wet? You sure the gauge is good? Are you doing the test with the throttle open and a battery charger hooked up?

 

Didn't do any of the tests with the throttle open. Just reached in the window and turned the key.

I have no idea what's going on with these numbers. The gauge is one I've had for years, and it's never been a problem. The only thing I can think of is maybe leaking injectors washing out the rings when it sits, but that seems improbable to me

 

I don't have a clue what happened, and probably never will. The car has been running fine since. The battery was low and needed charging, so that's the only thing I can think of, but I don't see how that would effect the compression.

Oh well. Mysteries of life, etc, etc...