PeachParts Mercedes-Benz Forum - View Single Post

tcane · #3 06-03-2002, 01:46 AM

M-B only provides compression specs for an engine that is hot with 80 degree C coolant temp. (or very warm anyway since it takes time to remove glow plugs or injector nozzles and install the compression gauge fitting). Normal compression is 319-348 psi and I've seen readings as high as 400-420 psi. Minimum hot compression is 218 psi.

I found that you can expect a 20-40 psi lower reading on a cold engine if the compression is toward the lower end for a hot engine spec of 319 or so and 30-50 lower psi if the hot compression is toward the higher end of 375 +. If the used engine is in minimal condition, I would be very leary of cold compression of 190-200 psi. If the used engine has been sitting then it could have low cold compression that MAY improve when the engine has been run for a while. My numbers are for outside temps of 60-70 + degrees F. If it is colder than that in your area of Canada, then the compression readings will be lower.

The type and condition of the compression gauge used can also make a difference in the reading you get. It would be helpful if you are familiar with the compression gauge you're going to use or the person you borrow/rent it from.

Will the seller of the used engine give you a refund in case it turns out to be in worse condition than known?

Good Luck!
Tom