Oil level?
 

First time poster here. I'm a proud new Mercedes owner. Just bought a 1981 300D a few months back. Only 100k miles.

About 3 weeks ago I changed the oil and filter. I filled it up with the recommended 7.5 quarts, let the engine run for a minute or so and checked the dipstick, which read just right. Before the oil change I was leaking a bit of oil on the driveway (had a wood board down) but after the change the oil drip stopped. I think it was just tightening the plug with a new crush washer that did the trick.

Last week I checked the oil (cold engine) and was surprised to see the dipstick reading almost empty! It shows a little bit of oil, maybe half an inch up on the dipstick which is well below the lower marker. I guess the obvious thing to do would be to just fill it right up but I have some doubts about the reading. First off, that oil has to be going somewhere. I'm not dripping oil and there is no smoke at all coming off the hood or exhaust. So what's going on? Could it be that the dipstick is reading incorrectly? Then again it did give me a good reading only 3 weeks back.

Unsure of what to make of this, I added about half a quart today and the dipstick showed no change in the oil level! I'm really scratching my head. Any thoughts?

PS. The oil pressure gauge on the dash reads full.

Welcome to the forum and congratulations on your purchase!

Here is the "official position" on measuring oil level: http://www.w124performance.com/service/Index/Resources/00.57EngineOilLevelSI.pdf.

So try measuring the MB way and see what you find. I find that cold and warm readings are comparable on my cars....but perhaps yours is different.

Any possibility that you're rapidly using oil without seeing any smoke?

What weight oil did you use? Synthetic or dino?

Looks like a nice car, pictures of the engine might help Id where it is going....take your milage with a huge grain of salt!

@Shertex, Thanks for the instructions. I followed them to the T and here is what it gave. It's just about the same as when I was reading it cold. I guess it must be going somewhere. But like I said I don't see any smoke and it's not dripping any oil...

@ cooljay, I put Shell Rotella 15W40 dino oil. I'll take a few pics tomorrow when the sun comes up. I noticed quite a bit of built up oil around the oil pan gasket, also a bit of black around the oil cap, so I'm sure I'm losing some from there. But I find it hard to believe that I could lose what seems like almost 7 quarts without a drop on the driveway or any sign of smoke... Also I don't know what to make of the fact that I added 1/2 a quart earlier today and the level didn't budge...

Ya the odometer is anybody's guess as to whether it's true or not. I like to believe it is :)

I was going to say if you were using synthetic or a low weight oil, it will burn off really fast.

Sometimes a low mile example may be worse then a 300k example....yours may be suffering from this. If your going down the freeway....you may not notice smoke....specially if you have an egr system....it may just be sucking the smoke right back into the intake...

While running if you take the oil cap off, do you notice a lot of blow by?

Ok, you say almost empty. Do you mean it just dropped to the bottom of the dip stick? Since you have a non-turbo they are geared pretty low and spin over fairly fast on the highway. My 1979 300D used to burn a fair amount of oil if I did a lot of highway driving at or above 100km\h. And this was without any sign of smoke.

Showing a half inch on the stick is probably still a long way from empty. Wet sump oil systems can run at idle with a lot of it missing and still maintain full oil pressure. Higher engine speeds can suck the sump dry more easily. Add a quart or half quart at a time until you get up to the recommended level.

That oil has to have gone somewhere. How much driving did you do in between checks?

To quantify things, find out (someone will know) the volume difference between min and max marks on your dipstick, start with it at max level, and see how many miles it takes to us x quantity of oil. Of course be aware of the fact that some of our cars use oil from max down to about halfway on dipstick, then level off.

At any rate, it certainly sounds like you're using oil at a fairly rapid rate.

Ok well it must be burning oil. I thought I would notice smoke but it sounds like that's not always the case. From the photos here it looks like I'm losing a bit around the oil pan but like I said earlier, not enough for a drip.

I've probably driven about 1000 miles since the oil change. Thanks for pointing out that an inch up on the dipstick is a long way from empty. I'll go ahead and top it off, adding 1/2 a quart at a time.

@ cooljay, how do I do a blow by test and what does it indicate?

from tip of the stick to the top mark is 4 quarts...
from bottom mark to top mark is 2 quarts.

if you were still showing at all on the stick, you still had at least 5 quarts in the sump, and were not in danger of running dry, but it's not a good situation.
pull your valve cover, and change the gasket, adjust the valves, and clean out the tube that the vent line plumbs to.

On a 617 I believe from min-mark on stick to max-mark is only about 1QT. On the later engines its closer to 2.

Hmmm

all of mine 79 - 85 had a 2 quart range between marks...

On my OM617 it is ~1 quart. Always has been.

The M103 has a ~2 quart range from max to min.

To do a blow by test, just remove this oil fill cap and see if you get a lot of smoke out of the top....place the cap back on, with out locking and see if it dances back n forth...

I agree, 1qt between high and low.