Where does all the oil go?

It burned.

When you removed the filter I presume that there was a significant quantity of oil inside of it. Not knowing how large the filter on a Mercedes 240D might be, I’d guess at least a quart, and maybe more.

But since you mentioned that the oil was black, I’m also going to agree with @El_Cadejo that there seems to be some cylinder leakage (bad or failing rings, maybe?) of combustion residue into the oil, and a fair amount of oil being burned, too. You also didn’t mention checking the oil level prior to draining it, so it was probably low to begin with. That could have leaked from the drain plug or a pinhole leak in the oil pan, through the cylinder rings, as already suggested, or at the valve covers.

It did show nearly full before I started. I’ll have to keep a better eye on oil level. It’s only got 136000 miles on it, fairly low for a 1978. Do they flush engine innards on old cars sometimes?

Oil pans are pretty big and flat like a casserole dish. So there can be a lot of volume in not a lot of vertical when you stick the dip-stick in.

When I do an oil change I try to do it a few minutes after I drive the car so it is still warm – not burning hot. i also park the car in my driveway so the drain plug is the lowest point.
You can have dented oil pan which will prevent some oil from flowing out.

I do something else but I am sure it is not recommended. After I finish draining the oil. and the filter and plug are still off, I bump the starter to turn the engine over a couple of times. More dirty oil always runs out.

You know oil is burning because it makes smoke.

Only 136,000 miles on a 1978 Mercedes? I don’t believe it. I flat don’t believe it.

That’s a 36-year-old vehicle (assuming it was actually new in 1978, and not 1977, which would make it a year older), and an average of less than 3,800 miles per year. Who drives that car that little for that long?

Even in my own case, with a 3-mile commute to work each day, 6-mile round trip, plus normal driving around town (and a trip out and back from Wisconsin every year) I put 10,000 miles a year on my car.

If the pedals or the upholstery on your car look the least bit worn, then I suspect that the odometer has rolled over once.

OOO…. It just occurred to me. You changed the oil when the car was cold and let it sit. Then you filled it and restarted to fill oil passages then turned it off again. Right? Do you live in a cold climate? If yes, then the oil could be very viscous. When you started it the oil pump pushed the oil up to the valves and valve covers.etc. and did not have time to flow all the way back down to the pan before you dip-sticked it.

How is it today?. Are you over full?

This morning, the oil level is about ½” above the full notch. Black as can be :(. I did run it about town yesterday to take the old oil to the recycling place, and to get some fuel. I hope being a little over-full doesn’t hurt it. I’m told these old diesels are quite robust. Input on this would be mightily appreciated!
I believe the mileage to be pretty close, the upholstery is in really good shape, but the horse-hair stuff inside is .. Not so good. Took nearly a wheel barrow full out from under the rear seat alone. It sat for years apparently after the original owner passed away and the guy I bought it from got it. I actually bought it from his wife who was having it hauled away because he wasn’t doing anything with it and a tree had fallen on it. (Two years ago) I had to replace all the brakes because the calipers were frozen, master cylinder, vacuum fittings were dry rotted. All consistent with long storage. I am still limiting it to short trips “sea trials” before I put it on the road.

Ask the Irish, “oil tell ya, to be sure, to be sure”

Most modern manufacturers have you check and drain oil when the the motor is up to normal operating temperature. This frees the most to drain as it’s hot and able to flow better.

At least some oil loss over time is normal. More will be lost the harder the car is driven.

Blow by causes oil to enter the combustion chamber. A certain amount of this is also normal.

Certain oil leaks on older cars can be normal. Modern mass production cars shouldn’t leak a drop.

If you added the replacement oil too quickly and without checking the level as you went along you may have overfilled as cold oil takes time to settle and make an accurate indication.

When I change the oil myself in my car I err on the low side. drive the car, allow the hot oil to settle, check and add if needed. If needed I repeat this process.

Overfilling can be as bad as running with a low level.

However bear in mind that most modern, simple production engines don’t care if they are running a little high or low.

Also, did you factor in the oil left in the filter?

I wouldn’t worry too much as the old school Mercedes-Benz diesels are nearly indestructible. Just be careful to not run them out of fuel, A much bigger problem with diesels.

,.,

Having the crankcase a little overfull won’t hurt this engine. It’s a low-injector-pressure diesel IIRC, so it will just burn whatever oil gets past the rings. There are no plugs to foul, so no harm there. You might want to check the breather apparatus after driving it to make sure it’s not spewing oil everywhere. If the PVC valve gets clogged then it could build up pressure in the crankcase, which wouldn’t be good; but the most likely outcome would be that the valve pops out and the engine shoots some oil out the hole.

I do recommend a compression test on the engine. Oil loss without a visible leak could implicate bad rings, and in a diesel you might not be able to tell as the car will smoke anyway.

Dumb question, but are you sure you’re using the right oil? Diesels often require different lubricating oil from that which gas engines use.

While it is synthetic, I am still sticking with Rotella, a diesel oil. it is a 5–40 rather than the 15–40 for the dino-oil. It is my hope that it will make it easier to start in the winter. Of course it has a big honkin’ battery to turn it over too! :) This is turning into the most expensive $500 car I ever had!

@majorrich Well, it sounds like you are doing everything right, or at least right enough. Remeber, these engines are notoriously tough and long-lived. I think you’ll be fine.

If you’re worried about the dark color of the oil, you can do an engine flush, or you can just wait it out and change the oil a little more often than usually. I’m thinking that there’s gunk inside just from the car sitting so long. It should work itself out; the only problem is to ensure that whatever bits of crud break free get caught by the filter instead of some sensitive part. Make sure you keep a clean filter in the engine and you should be fine.