OM616 Oil Consumption Question (1 qt/100-200 miles!)
 

OK, here's the deal. The engine in my '74 240D runs great. I've done work to it in terms of normal maintenance items (fuel filters, oil/filter change, replaced primer pump, fuel hoses, valve adjustment, new GPs, etc). It starts pretty well but when cold can be just a little rough and does have blue/grey smoke when idling cold which goes away when warm and hot. It always starts after just 1-2 revs after pre-glowing when cold and the same way when hot without any pre-glow needed.

I just did a warm/dry compression test "by the book" method and these are the results:

#1 24 bar
#2 24 bar
#3 24-25 bar
#4 22 bar

Spec is 22-24 bar with no more than 3 bar difference between two cylinders. Basically it passes the compression test fine, but I could probably have predicted that since it sounds super when it runs, smooth and the normal "sewing machine" sounds when running (I don't say it is quiet but what OM616 is).

It was running cool when I bought it due to a stuck thermostat so I replaced it and it now comes right up to 175± on the gauge and stays there when runnning. It was also nailing like mad when I got it but a set of rebuilt injectors took care of that 100%. Also, I checked the vacuum pump hose and it appears to be intact and not leaking oil through the line to the intake. Blowby is not bad, you can loosen the fill cap and it does not dance or even really lift, but if you remove it you will see a reasonable steam plume. Certainly not what I call excessive.

So, its only fault now is the blue/grey smoke and an appetite for motor oil that is puzzling (as the title says, one quart every 100-200 miles). Oh yeah, and it has no real leaks. I mean it will have a single drop or two on the floor after shutdown and sitting overnight, that's all and none while running.

I have no experience with faulty valve stem seals and am wondering from others here if it is possible that oil consumption at that rate could be caused simply by bad seals or do I need to look elsewhere? and if so where?

I also know from experience these early 616's do consume some more oil than the later ones for a variety of reasons, but I would expect the rate to be closer to a quart every 500-1000 miles on such an engine rather than 1quart /100-200 miles. I owned a 240D before that used a quart about every 300 miles and did so for years without a problem but this one is even worse than that!

At that rate without constant blue smoke, its probably an external leak.

Get a glove and run your finger around the inside of the tailpipe to see if there is liquid in it.

I updated after you read it and included a note saying there is no measureable oil leaking from it. I just did the tailpipe test now and nothing but powdery black soot was on my glove.

And blowby mainlines straight into intake, doesnt it? You can slow down blowby loss by packing the breather pipe gallery inside the valve cover loosely with wide mesh stainless steel wool like pot scrubber stuff.

Yes, it does, but the first thing I tried was to retrofit an oil separator from a VW TDI breather outlet onto it which did nothing to slow down the rate of consumption so I concluded that the amount of oil being drawn into the intake was not causing the excessive level of consumption.

I don't know, either valve seals or a bad oil ring would be my only guesses.

What kind of oil are you using. That makes a lot of difference. The newer oils aren't made for that engine.

But there is no harm in using them.

Rotella 15W40.

Is there any way to test for a bad oil ring?

How long has it been since this much oil loss has been happening? What kind of driving are you doing when oil loss happens? Has the car or engine been over heated??

Is it possible you are sucking oil threw a cracked diaphram in the vacuum pump?

As a test consider putting in straight 30 or 40 weight diesel oil on the next oil change. If consumption drops way off the oil control rings are weak. Oil usage should go to about 1/2 the present consumption. If if there is something wrong with them.
Its warm enough to run the heavier oil this time of year. It becomes really interesting if oil usage were to remain identical. Just adding the straight oil every 100 miles or so would also start to show if there is any difference over time as well. Just not as defined.

I only have owned the car for a couple of months and have only driven it 600 miles. Though my driving is mixed it does seem that it consumes at a greater rate at high speed highway driving.

It's been doing this since I bought it and the PO did say it burned oil for him too. Don't know the history of it other than that.

Nope, I've checked that (it is noted in the original post). It's a good thought though.

I was cosidering this. I could not find a diesel rated 40 weight oil though I could find rotella in a straight 30 so I might start adding that and see how it does. I have also heard that using heavier oil with bad rings can actually speed the consumption rate though since the heavier oil tends to leave a thicker coat on the cylinder which gets left to burn.

I supposed it couldn't hurt to replace the seals and see if that helps. The replacement parts are cheap ($20±) so it is only a matter of the time spent doing it.