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  #1  
Old 12-14-2006, 11:13 AM
rsd rsd is offline
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OM621 compression

Hi all ,
again I just have a question regarding my old 67 MBZ 200D diesel. Things I've installed recently: new timing chain , camshaft, new fast glow plugs , new starter wires , new battery , new fuel hoses , e.t.c. Cold start of my 200D became not a problem ... until now ... winter .. well, temperature dropped down and I started to experience the same old problem. I've gotten myself a harbor freight compression tester. did compression test on warm engine yesterday:
300 , 290 , 310 , 295 psi. 1 to 4 cylinder respectively.
so my question is:
Are these compression numbers low enough to make winter cold start impossible ?
maybe somebody knows what are they supposed to be for OM621 ?

Currently I see that if temperature drops below 32-30 F I just can't start my old MB without plug it into power outlet first for 2-3 hours, then she starts right up so far...
and if the compression is not so bad then maybe someone could direct me where else could I dig to get the reliable winter cold start on these vintage engines ... lets say, compression rings replacement maybe ? so I wanted to listen some advises before I start doing something drastic.
Thanks a lot to the members of this forum for their replies .

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  #2  
Old 12-14-2006, 11:16 AM
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I would have thought those numbers would be good enough to start the car in those temperatures. Try adjusting your valves if you haven't already. More importantly, let's see some pics of your car!

Scott
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1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
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1995 Ducati 900SS (sold)
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  #3  
Old 12-14-2006, 01:48 PM
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My 617...

Will start down to 25F without plugging in with the following numbers:

360, 260, 220, 100 (yikes), 260. Compression I doubt is your problem. As mentioned, check valves and fuel delivery. Good luck!
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  #4  
Old 12-14-2006, 10:50 PM
KCM KCM is offline
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You are concerned about something that is not a problem. These models are cold-blooded and are very hard to start at temperatures below freezing without plugging in a water heater. Later models, such as the OM616/617 engine, are newer technology and will start easier below freezing. Starting hard when cold is their nature, and the nature of any diesel.

In answer to your initial question, the Chilton repair manual says the compression shold be between 284 psi and 327 psi. The book says that individual cylinder pressures should not vary by more than 45 psi. Sounds like your pressures are right on the nose. As Scott98 said, check the valve clearances, 0.004" for the intake and 0.016" for the exhaust. The Chilton book says to increase the intake to 0.006" for cold weather below 5 degree F.

I would say either plug the water heater in, keep it in a heated garage, or park the car during cold temperatures.

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