My 1977 240D, which has been running flawlessly and with normal power for a 240D, has decided to not start. It has over 200,000 miles. I did dry and wet compression tests on the cold engine. Here are the results:

Cylinder Dry(psi) Wet(psi)
1 150 340
2 200 360
3 140 360
4 180 350

Do these results doom the engine as bad?? What are my options?? I wish it would be a head pull and rebuild only but are these numbers saying rings, rings, rings.

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Dionysius

Did you run it low/out on oil?

the wet results are fine and there is little variance between each cylinder. Dont see anything wrong here

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1981 300SD 512k OM603

No. It does use 1 qt per 700 miles. Car is a German model. No power steering, no a/c, very basic.

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Dionysius

Service manual says minimum compression should be 220 psi. The dry results are failing this spec. Will I be able to get it to start??

I removed the injectors to perform the test. I am going to get injectors professionally serviced. I am replacing all glow plugs and 80A fuse. I have brand new primary, secondary fuel filters. New primer pump. Ball check valve is chirping when I stroke the primer. No air in fuel.

My concern is if I am too low on compression on the dry test with cold engine to enable starts.

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Dionysius

the 220 figure is the minimum cold for reliable starting.

The cylinders and rings could be shot or The rings might well be stuck. Either of These would not happen overnight and not normally at such low mileage. I would suspect the following:
1. Lack of oil changes in the normal mileage and or run low on oil. (worn engine)
2. Lack of air filter changes. Diesels are very susceptable to ring and cylinder wear from dirty air. (worn engine)
3. Stuck rings from #1 or from use of improper lubricants or from running wvo.

If it is stuck rings it may respond to lucas oil synthetic (stp like) stuff or perhaps a switch to synthetic diesel rated oil.

If you are not running a proper diesel rated oil just a switch to a good diesel rated oil such as rotella might do it.

If its a severely worn engine the only solution is an overhaul. The only way to determine with no doubt is to tear it down and measure.

If you tell us completely and accurately how you have been changing the oil and what you have been running and your air filter habits we can help you evaluate your situation.

Good luck.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Are you sure your glow plugs working when the car failed to start?

The M-B specs for compression are based upon a warm test (80C coolant temp) not cold. Still, your readings do seem low, however it is possible that just the fuel mist would be enough to bring them up to spec while cranking and since you tested them cold without the injectors you really don't know what compression is warm or with fuel.

If it were my car I would confirm the function of the GPs and try to restart it. If that fails, I would adjust the valves to make sure they were to spec and try again. If the car was running one day and just wouldn't start the next day I would suspect GPs are the cause, not a compression problem. I wouldn't spend money on having the injectors serviced until I got the car running again first. You can always buy rebuilts for about $40 each once you have sorted out the starting problem which is not likely to have been caused by the injectors.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz