I'm a newcomer to the world of Mercedes diesels, and I tried searching the message board for a similar problem but couldn't find anything that was related.

I was wondering if there were any places in the crankcase ventilation system that could be prone to blockage? I have a 1979 300D that was passed down to me from my dad with pretty bad oil consumption (it loses a quart every ~400 miles), and there seems to be a good number of oil leaks. There is a bit of oil escaping from the valve cover gasket (looks like there's oil spray pointing upwards onto the valve cover about an inch). There's also enough oil leaking down the passenger side of the engine to coat the engine block from the exhaust manifold down -- I can't really tell where this oil is coming from . After driving, there is a little bit of oil around the oil filler cap on top of the valve cover.

My guess is that excess pressure in the crankcase is forcing the oil out, so I suspect something in the system is blocked? I did take out the breather hose that runs from the valve cover to below the air filter and made sure it was clear, along with both rubber elbows. There was a bit of oil in the intake manifold as well. Is there anything else I could check?

Within the past 6 months I've replaced:
Oil filler cap (now have a new black plastic one)
Breather hose rubber elbow
Valve cover gasket twice by an indy mechanic
Engine shutoff diaphram (not sure if that's the proper name for it, probably unrelated to my problem)
Did two oil & filter changes

The car has ~125kmi on the odometer, and I *believe* that is accurate, as the car was not heavily used by my dad or the previous owner. Engine starts reliably down to 45 degrees or so without a block heater. It could probably go a few degress lower, but I've been using the block heater. It will definitely not start below freezing without help. The car drives pretty well I think, with no visible clouds of smoke behind me . I know a bit of oil leakage should be expected, but I'm afraid I'm going to kill a seal with all this excess pressure .

I forgot to mention my oil pressure while driving. When warm, it hovers at probably 25 psi at idle and jumps back up to 45 psi when the engine is fast enough to move the car (I'd put this at maybe 1500 rpm, but as this is my first diesel, I have a hard time guesstimating the engine speed).

Thanks for reading through my long winded post

Welcome to the forum.

It's not all that easy to diagnose the issues you have via wire, because of the nature of them.

However, it is unlikely that there is any "blockage" in the system that prevents the crankcase vapors from escaping. You have checked the obvious culprit and it is clear.

When a diesel engine wears, it gradually increases the amount of "blowby" past the pistons and into the crankcase. This blowby must go somewhere and it is designed to go up to the valve cover and escape via the breather hose. Of course, it takes some oil with it; quite a bit of oil in the case of engines with quite a bit of blowby.

Your oil consumption indicates that the engine is consuming oil past the oil rings on the pistons and/or blowing the oil up through the breather, and/or leaking oil from old hardened gaskets.

Furthermore, the inability to start the engine, without a block heater, below 32 degrees, is also indicative of low compression. I am making the assumption that your glow plugs are all in working condition.

To confirm all of this theory, it would probably be beneficial to perform a compression test on this engine. Then you would know where you stand.
If you find some low numbers, the high oil consumption begins to make some sense.

Thanks for your insight -- I was hoping there was an easy fix (I know that on Volvo engines for example, a restricted flame trap causes excess crankcase pressure), but I guess there isn't .

I haven't had a compression test done, nor am I in an area with many mechanics knowledgable about diesels, so I may have to wait until I go home (I'm a college student at Penn State) to have that checked out. I am pretty certain the compression is going to be low in one or more cylinders, and I read up on blowby in the forums - I just thought the crankcase ventilation system should be able to cope with any of the blowby gases produced. I guess it can only handle up to a certain amount, and quite sadly, my engine is probably putting out more than that. I guess I should be thankful the engine still starts .

There is definitely oil going up the breather tube (oily residue on the inside of the tube, elbows, and in the air intake).

I did change my glowplugs recently (I actually went to parallel glow plugs in December), so the engine is probably not in good shape. (I'm also 15W-40 dino oil, Mobil Delvac, which probably doesn't help the starting situation any.) The rest of the car probably isn't in good enough condition to warrant rebuilding the engine either, sadly .

It is hard to determine where you may be losing oil but are you burning oil?

With the rate of 1qt/400 mi. you would have to have a noticable cloud of smoke coming from your exhaust. Also, a simple check for extreme blowby would be by turning the oil filler cap to unlock it then starting the engine and watching the cap for "dancing".

What do your oil cooler lines look like? With all that oil on the left side of the engine, these may be suspect. If they are leaking, don't drive it until you replace them.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

The crankcase ventilation copes with the blowby just fine, unfortunately, the oil separator does not. Once a sufficient amount of oil is escaping the crankcase, the oil separation capability is not present anymore and the engine burns the oil. This is, of itself, not a terrible thing, until it progresses to where the engine actually continues to run on the oil from the crankcase.

Since your glowplugs are all new, this lends further credence to the weak condition of the engine.

The 15W-40 dino oil isn't going to give you any problems starting the engine until it gets down around 20 degrees or so. Then you might begin to notice some reduced cranking speed. Of course, you need all the speed you can possibly get with that engine. If you intend to keep it for awhile, my recommendation is to keep a large battery (850 CCA) that is not more than two years of age in it at all times.

You probably don't want to run synthetic in it due to the amount of oil consumption, but, if you have to start it routinely below 32 degrees, with no block heater, you might reconsider.

You have made a wise decision not to invest in rebuilding the engine if the body does not warrant it.

I can't do the oil cap test yet (it's cold and dark ), but there isn't a noticable cloud of smoke from my exhaust, though there is a noticable puff when I first start with a cold engine. I've tried flooring it on highway onramps and hills and can't make it smoke noticably during the day. It's noticable at night if there's a car behind me however.

Again, can't check these till it's light outside, but I meant to say the passenger side of the engine had a lot of oil on the outside (the side of the engine with the air cleaner). The other side of the engine block (driver's side) is actually pretty clean. I'll still check the oil cooler lines anyway, since it's probably a prudent thing to check .