Compression test results on my 1982 300D
 

I had a local Mercedes shop do the dreaded compression test on my car yesterday but the results turned out pretty good. The car has 205,000 miles on the odometer, but sometimes the odometer doesn't turn so I'm guessing it has more like 240K miles. Here are the readings in lbs/in2:

1. 376
2. 350
3. 350
4. 350
5. 340

I also had them test the pop pressure and spray pattern of my injectors. Pop pressure was 1950 on all injectors except #1 which had 1925. Two injectors had a poor spray pattern due to dirt and the mechanic cleaned them and now they're good. That's worth mentioning because recently I ran a bottle of Diesel Purge through the system so apparently even Diesel Purge may not be able to fully clean injectors.

The only weird part is that on my receipt it says new compression specs are 22-24 bar. I looked up the conversion factor and apparently this would be only 319-348 lbs. :confused: I wonder where they got these numbers.

I will take a guess.... When engines are new they are not as close fitting as they are after proper break in. Your compression and mileage typically continues to go up through the break in process... So I would say you have done a good job changing oil... and your engine is in great shape....

I read somewhere the other day that Mercedes considers the minimum compression on these engines to be either 240 or 260 so yours is in great shape.

Leathermang, that's a good theory and I never thought of that, probably because somewhere on this forum I read that new specs are around 400 lbs. Maybe that's after break-in. I think I'll call my mechanic and ask him about this. Either way, I'm very pleased with the results, especially at 4500 ft of elevation where compression readings should be a little lower. By the way, on my receipt it also says that 15 bar (217 lbs) is the critical wear limit which seems really low to me.