Compression test question

[BenI]

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

[JP Noonan]

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.