my 300TD is using oil - PeachParts Mercedes-Benz Forum

#1 11-02-2002, 10:21 PM

Hello everyone, I have a Mercedes Benz 300TD with about 190,000 miles on the odometer, and probably just over 200,000 real miles (odometer was broken for a few months). I have owned the car for about 3 years now and the car has a number of problems but the biggest is its oil habit.

The car has always consumed between 1 and 0.5 U.S. quarts between fill-ups. It seems to consume less oil when the majority of driving was done on surface streets. Freeway driving “seems” to increase oil consumption slightly. Initially, the back hatch would be decorated with small spots of oil, but upon replacing one of the oil hose from the filter to the cooler, the valve cover gasket (also adjusted the valves, been about 2 years since that time), and the sump gasket, the black spots have cleared up. However, the underside of the vehicle on the driver’s side of the drive-shaft continues to be wet with oil. The car smokes at start-up and when the accelerator pedal is depressed. It also smokes a little when its at idle even when warm. The smoke appears to be white or gray, not black. A recent compression test yielded average diesel compression in every cylinder (I don’t remember numbers, just that the values were good). Once, parked nose up on a steep driveway, a stream of oil poured from the interface between the engine and transmission. The bottom of the engine is always wet with oil, so it’s tough to tell what’s leaking on the engine. Parked, the car only spots the driveway, never leaving puddles. The car starts easily, once the glow-plugs are warm (first start takes time and is noisy, but every start after is smooth and quick).

To sum up, it has good compression, runs strong, but smokes and uses oil like mad. My first impulse was to replace the rear main seal (wet underside is a strong indicator oil loss is through a leak), but I have been told that both the timing chain and valve guide seals may be contributing to the picture. Should I jump in and replace the rear main (job looks scary)?

kerry · #2 11-02-2002, 11:05 PM

You'll need to pull the engine or at least drop the crankshaft to completely replace the rear main seal. I believe you can replace the bottom half without dropping the crank. You then have a 50/50 chance of solving the problem if that is what it is. It'd do some closer investigation before taking that route.

leathermang · #3 11-03-2002, 08:11 AM

In that same plane across the back of engine are at least two holes which line up with the oil passages in the engine... they are there for cleaning the passages during a major overhaul... they are sealed by a couple of interference fit balls pressed into them... so oil could be coming from that area on the car without it being the rear crank seal....
Oil leaking out us sure better than burning it...

psfred · #4 11-03-2002, 08:58 AM

The oil filter housing gasket can leak on these cars, too, running oil down the rear of the block. I'd fix that before going after the rear main.

Best thing to do is to pressure wash the engine carefully to remove all the old oil, then spray it down with foot powder. This will coat the engine with white powder -- black oil leaks will be VERY obvious.

Run it for a while and see where the black show up.

A rear main leak will only put oil on the tranny and back -- if the engine pan has oil on it, most likely you have a leak somewhere else.

Slow, noisy starts and smoke at idle warm with good compression make me think of a worn timing chain and hence late valve and injection timing.

Peter

psfred · #5 11-05-2002, 08:18 PM

Warburto:

Checked with my local Benz guru and he had this to say:

Any leak on the oil filter housing will look like a rear seal leak. Things to look at:

Oil cooler line fittings. These are pipe threads, filled with a sealer. The sealer goes bad and they start to leak. Hans takes them out (a huge pain) and re-seals with the addition of a copper washer between the fitting and the housing. Cures leak.

Pressure line to the turbo. Runs from filter housing around the back of the engine to the turbo. Banjo bolt seals on oil filter housing often starts leak by this age, easy cure-- remove bolt, replace washers, re-install bolt. Also looks exactly like a rear seal leak except starts too high.

Oil pressure sending unit leaking.

All will get worse on a long highway trip due to oil temp.

If you do, in fact, have a rear main seal leaking, go to WallyWorld or K-Mart and get some "Engine Restorer" -- trake name -- and add to the oil. Repeat on next oil change. The seal almost always will swell back out enough to stop leaking, and it appears to be permanent. Much cheaper, at any rate, than a new rear seal!

Peter

kerry · #6 11-05-2002, 08:41 PM

Peter;
I have a leak at the oil cooler line fittings on my 77 300d so I'd like further clarification on the repair. There is a nipple that comes out of the oil filter housing to which the oil line compression fitting attaches. I assume it is that nipple which has pipe thread and sealer. Two questions: Where would a washer go on that nipple. I can't visualize how a washer would help seal a pipe thread unless it went behind the nut on that nipple that threads up against the filter housing. Even in that position it seems that the sealer on the threads would be the main bulwark against oil leaks.
Why is the job so difficult? It seems fairly simple: remove the oil cooler line, back out the nipple, put on teflon tape or something similar and reassemble. The only thing that concerns me is that some of that sealer may get in the oil galleries.

psfred · #7 11-05-2002, 09:05 PM

Kerry:

The angle and the fact that the sealer is only leaking -- it still glues the thread down! The copper washer goes between the flange and the housing -- there is enough of a flat there to seal some, and it seems to prevent leaks. I don't know, Hans swears by it.

Shouldn't have any trouble with the sealer coming off, quite the opposite. You may have trouble getting the nipple out!

Peter