Keep driving my 79 300d with oil leaking? - PeachParts Mercedes-Benz Forum

mrbisset · #1 04-15-2009, 09:45 AM

I have been working on my 300d for the few months I've owned it and got it running ok. i drive it to work everyday as long as its not too cold and it doesn't start, but its leaking oil pretty bad and burning it too. Thanks to help from this forum, I got the car started after a few years of it not driving, ran diesel purge in it, replaced the battery, and adjusted the valves. The starter is intermittent and it doesn't engage about 75% of the time. I like driving it, but have been thinking about how long can I keep it going...I have done a compression test on the front 2 cylinders and they are around 210 psi...pretty low. I couldn't get to the rear glow plugs easily so didn't test them yet. But when I loosen the oil filler cap while idling, it wants to blow off! a sign of blown rings? the other problem is that I am leaking oil down the passenger side of the engine pretty good...its covered in oil and I am adding about 1 quart/100 miles. i checked the valve cover gasket i replacedand it looks ok, no signs of leaks...it has to be coming out somewhere else. I do all the work I can on it myself, but being my first Benz, i don't know where to start troubleshooting oil leaks and am thinking of have someone else look at it.

vstech · #2 04-15-2009, 10:16 AM

I'd look at the intake manifold, with that much blowby, you are likely flowing quite a bit of oil into the crankcase vent. with a leaking intake gasket, you are sucking dirty unfiltered air, and dumping oil out the thing. pull the air cleaner off the motor, it's likely the rubber mounts are shot anyway... and clean everything free of oil. a pressure washer helps here, but a good scrubbrush and some degreaser will do fine with a garden hose. then look for the path of the oil.

Diesel911 · #3 04-15-2009, 01:25 PM

My biggest source of an Oil leak turned out to be the Valve Cover Gasket. And, I suppose if there was a problem with the Valve Cover Gasket and you have high Crancase Pressure caused by blow by it would even leak more.

If you have not done a Valve Adjustment yet it is possible the Clearances are tight enought that it is holding some Valves slightly open. This would result in a compression loss.

I found out many months ago that my Volvo Diesel that had sat for a year (until I got around to changing the leaking IP Drive Seal) and also partly due to my Thermostat sticking open (creating a low operating temp) had developed a case of sticky rings (this would also effect the compression).

I removed the Golw plugs and used a Meat Injector Syringe with some Vacuum Hose on it to inject about 1/4 cup of Marvel Mystrey Oil into the Cylinders in hopes of disolving some Carbon or otherwise unsticking my Piston Rings.
I let the Car sit for 4 days and repeated the above and let the Car sit for 2 more days.

With the Glow Plugs still out I cranked the Engine over to blow out any excess Oil and prevent a Hydraulic Lock.

Put the Glow Plugs back in and took the Car for a 1 hour drive on the Freeway. (I also had changed the Thermostat.)
The Freeway drive only brought some improvement but over the next week it gradually got better.

I mention the above as it could be possible you low compression is due to stuck compression rings. Also the Marvel Mystrey Oil does not cost much. But, you do need to be able to pull all of your Glow plugs out or be willing to pull the Injectors and replace the Heat Shields.