6610g

I am new to this forum but I am looking at a 1982 300SD and the dealer that has it told me that the compression values were 115 on 4 cylinders and 120 on the 5th. What are the compression values suppose to be? I thought that they should be in the 300 psi range. The car has a good body and everything electrical works including the AC. The vehicle does have 200K miles on it.

Steve Clark

Unless it somehow became a spark-ignition (gas) engine,that's about half what it should be.


Per the OM617.95 manual-

"test values for engine at operating temperature in bar gauge pressure (atu)

Normal compression pressure 24-30

Minimum compression pressure approx. 15

Permissible variance between the individual cylinders max 3

(1 bar = 14.508 psi)


Checking it cold will give noticeably lower numbers, but you should be about 20 bar (~300#) or more.



My '81 300TD had about 320# cranking pressure (cold) at around 250K miles.

6610g

Thanks Steve,

If this vehicle truely had a compression of ~115 lbs on all cylinders it should be very difficult to start and be blowing excess smoke, wouldn't you think?
The vehicle starts up fine and does not blow excess smoke. I don't think the mechanic that did the compression check new what he was doing.