Hi all,

In preparation for my cylinder head R&R, I thought I'd do a compression test before ripping it all apart and possibly spending $xxxx on a new head. I was not thrilled with the results (below). Engine was warmed (car driven) to 90C, shut down, injector lines removed. It was an hour or so before I actually began the compression testing, which then took another 30-45 minutes (for two runs.) I let each cylinder pump until the needle didn't rise any further. Here's the numbers:


Test run one:
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Cylinder #1 - 24 bar
Cylinder #2 - 28 bar
Cylinder #3 - 27.5 bar
Cylinder #4 - 25 bar
Cylinder #5 - 28 bar
Cylinder #6 - 27.5 bar


Test run two:
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Cylinder #1 - 25 bar
Cylinder #2 - 27 bar
Cylinder #3 - 27.5 bar
Cylinder #4 - 25 bar
Cylinder #5 - 30 bar (checked a third time and it was 28 again!)
Cylinder #6 - 28 bar


Service manual specs:
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Normal pressure: 26-32 bar
Minimum pressure: approx. 18 bar
Permissible difference between cylinders: 3 bar


Now, I wasn't overly thrilled with the numbers, I was hoping for closer to 30 instead of 25-27. But what concerns me more is the variation between cylinders, which was 4-5 bar! Well, if you toss out #5 on the second run as an anomaly, it's just within spec. But on the first round it was 4 bar. What do y'all think? Would the engine being cooled down for an hour or more make that much of a difference? I can't see how it could be done much faster, maybe 30-45 minutes at warp speed...? The temp gauge was 50-60C during the test, I think (wasn't paying attention at the time.) I put on the battery charger a couple times while swapping to the next cylinder, but cranking speed never seemed to be an issue.


Side note: The stupid service manual neglected to mention that although holding the "Stop" lever down prevents fuel from being released through the 6 injector lines, it DOES allow fuel to be pumped out the return line! You know, the little one from injector #1 to the fuel filter? I didn't notice (or locate the source) until the end of the second round, after a 3-foot diameter diesel puddle appeared under the car. AAARRRRGH! Blocking the line should force it out the return to the tank. Details, details.... **sigh**

Anyway - should I be worried about the results? Particularly cyl. #1 and #4?


Thanks for "listening",

Dave M.
Sacramento, CA
1987 300D - 229kmi (just got compression tested)
1987 300D - 236kmi
1984 300D - 207kmi