Hi All
I know that the prescribed procedure in to check engine compression with the engine warm.

I'm wondering why you can get valuable information by the checking compression with the engine at ambient temperature. After all, that's the compression the engine has when its first being started.

Shouldn't cold compression have a direct correlation with hot compression? Perhaps 50 psi less - or some other variable to the warm numbers?

Have any members checked their engine compression both warm and cold - and are willing to share the results?

When looking to buy a 123 that isn't running, it would be a great help to be able correctly interpet cold cylinder compression numbers.

All thoughts welcome!
Joseph

I personally think that cold compression is far more informative than warm compression. Cold compression will tell you how well the car is going to be able to start when it's cold. We all know a warm diesel will start much easier. I've never done a comparison but if you have bad compression on a cold engine and you can't get the car started it doesn't really matter what it is when it's warm.

__________________

I've only done cold on my W116. I posted the numbers in the past. I think they were all around 330psi. That's at a mile high altitude.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

absolutely not.


Commonly, this diagnostic test is used as an aid in determining the running health of each cylinder comparatively. It helps to understand things like "why is my engine shaking", "why is there lots of black smoke", "what is this knocking sound?"... .etc.

Certainly, you can learn something from the cold numbers and where there might be some weakness, but do not expect those numbers to accurately reflect the running health of each cylinder.

__________________

I've always measured mine cold. The numbers are only going to get better warm.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

agreed, but the differences may become exaggerated when warm... and you might conclude that compression is not the issue.

__________________

Hi
Would you care to share what numbers might be expected cold - with a good engine?
Joseph