Compression test question
 

Just checked the compression then realized the engine was stone cold. How much of a difference does a warm engine make on compression readings?

Im at 5000' and mine were 80, 90, 80, 80. I read that these should be about .86 sea level readings, so at sea level i would have about 93, 104, 93, 93 psi.
Thanks for any input! (Its not a big job, but Id like to hear that temp makes a good difference so mine would be reading higher so I can feel better about things.)

Ben

Comp test should be done with engine near operating temp (don't burn yourself now, but the rings seal better if the engine in warm), ALL the spark plugs removed, a full battery, the thottle plate jamed wide open, and the same number of rotations should be used for each cylinder. A bad cylinder can pump up to near what a good cyl shows, if you pump it long enough.

Don't feel bad though, I've tested motors cold because 1. they didn't run for years and even though I assume the motor was shot I wanted to know what I was getting.
2. I was in a jam with no motor in the car, I had to choose between engines that came from scraped cars.

Sea level: '72 1.7L sat for 8-9 years maybe 140,000+ miles (speedo angle drive was broken, but for some reason the PO kept writen down fuel amounts at fill-up for another year or two?), #1 115,#2 115,#3 70,#4 130 the 70 went to 90 with a spray of JB Catalyst into the plug hole.
'75 2.0L sat for about the same number of years, found out later it was just re-built before going into storage (maybe 1000 miles), #1 145,#2 150,#3 140,#4 150.

Granted when I say "cold" I mean Miami 85-90 degrees, sitting in the hot sun all day cold, so the motors were maybe up to 100-110 degrees? Also there is some varience with testers. The 1.7L was tested with a Craftsman gauge that was later grenaded by a "friend" who used it on a jet-ski, the 2.0L was tested with a mechanic friend's Snap-on "more dollars than sense" gauge.

Are you sure about the .86 factor, sound's low to me? Just off the top of my head, you may very well be right.