Diesel Blow-by

[tstarr]

I have a 1982 300SD Turbodiesel that I have done a substantial amount of work on since getting (2 years ago). I have noticed oil on the air filter the last 2 oil changes. I know on my last car, a Mercury, that was bad and ended up quickly having the engine gone. My 300SD has over 200,000 miles on it and I'm concerned and want to make an informed decision on engine condition to decide whether to keep the car or bag it and get another. I live in the DC area and the car has started fine in the cold weather and seems to run just fine. Any thoughts or tests I should run? I assume a compression test, but what numbers would indicate good/bad on the engine? Any other tests? Thanks for the help...

[Benzmac]

The only normal thing to do to the high mileage D's is check timing chain stretch and replace timing chain and cam gear if the stretch is over 3-4 degrees.

[stevebfl]

A compression test will be usefull to find whether there is a really defective cylinder. Unless you are very familiar with your gauge and an engine in particular it is very unlikely that you can tell if an engine is uniformly worn out or not. So many things vary the actual values.

Normally MB diesels have compression readings around 300-350psi. The gauge I use has always been higher than that around 350 -400psi. A cylinder running 250 with others running 300 would bother me.

After years of seeing diesels wearing out I have decided that the best gauge of future engine life is how much oil one uses and how much trouble it is to start the car when its 30 degrees out. If the motor is wearing out evenly it has a good future if it is using less than a quart every 1000 miles. At a quart to 800 miles I start looking for reasons. At below a quart to 500 miles the car will start poorly when cold and be a real ***** if it doesn't start in the first attempts.

[tstarr]

Thanks! I'll get the shop to check timing chain and compression and let me know the readings. The good news is that it really isn't using a lot of oil - much less than a quart per 1,000 miles. I'll post what we come up with.