240D burning oil intermittantly and sucking air - PeachParts Mercedes-Benz Forum

dieselBenz · #1 06-10-2005, 05:22 PM

This is regarding a 1975 240D (W115).

The engine was rebuilt 10,000 miles ago, and the whole time she ran like a top, with no oil use between oil changes.

Then suddenly she started burning oil (no leaks) and we noticed air bubbles in the fuel return line.

The other day we took her out and as soon as we started driving down a steep hill it started burning oil (engine started speeding up by itself). Then we leveled out and it smoothed right out. We drove it around and it rode like a dream. Then we were facing downhill again and it started speeding up by itself.

This has our mechanic with 50 years of mercedes diesel experience pulling his hair out.

Thanks for your time!

junqueyardjim · #2 06-10-2005, 06:52 PM

Your note is so dis-connected. All diesels "burn oil". That is their normal fuel. Is it also using crankcase oil? How much is it using? If you can see bubbles in the fuel return line I will say that you have terrific vision, much better then 20/20. But that has no connection to burning oil.
Now you say you started driving down a steep hill and it started burning oil. If the engine was running you were burning oil. Do you think perhaps the engine was speeding up because of that phenomenon known as gravity? All vehicles will speed up on a steep downgrade. Are you trying to say that on a steep downgrade where you are not accelerating the engine, that you got excessive smoke out of the tailpipe. That would indicate that the engine is using some oil. Could you please explain this problem better?

If it was easy everybody would do it

Junqueyardjim

dieselBenz · #3 06-10-2005, 07:46 PM

Yes, it is using crankcase oil. About a quart every couple hundred miles (Stopped driving it since problem developed).

It didn't use oil at all between changes, this was a sudden change.

By the engine speeding up by itself I mean the car was stopped, facing downhill, and without having the pedal depressed at all, the engine starts running faster by itself and blowing smoke.

The return line from the pump is clear plastic. A stream of little white bubbbles can be seen; more fuel, more white bubbles.

I'm not as concerned about the air, that we can probably figure out; the oil consumption is what has me losing sleep.

Let me know if that's not clear or for more info...

Thanks!

Palangi · #4 06-10-2005, 07:53 PM

Do a search on :

Pneumatic governor diaphram. You may have to search back several years.

dieselBenz · #5 06-10-2005, 09:58 PM

That doesn't seem to be the problem on my car.
I don't see the connection between the diaphram and sucking air (or burning oil!) anyhow.

I hope this can be resolved, I would hate to have to sell this car!

Perfect white interior, working instrument panel (& clock!), 4 speed manual tranny(!), 6 1/2" wide rims with new perellis...

we rebuilt the engine ourselves so I haven't put much money into this car yet (that's how I like it).

But why did it start burning oil suddenly?

rg2098 · #6 06-10-2005, 10:09 PM

Sounds like an IP issue. I wonder if oil is leaking due to worn bores.

dieselBenz · #7 06-10-2005, 10:23 PM

What is an IP issue?

After the rebuild, we changed the oil every 5,000 miles, and she didn't use a drop between oil changes. Then, after the 2nd oil change (10,000 miles) it went through a quart of oil in about 200 miles. No oil leaks to speak of.

The smoking and burning oil has always been intermittant, it runs well for a large chunk of the drive.

But like I said, last time we took her out, there seemed to be a direct connection between burning oil and facing downhill.

PatrickW · #8 06-11-2005, 12:08 AM

Does a '75 240D have a Cyclone Separator, or something similar...? That's a device that looks like a black beer can that is located between the tube coming out of the top of the valve cover and the tube going into the air intake.

The intent is to burn crankcase gases, but not oil. It allows the noxious gasses to get burned, but makes the liquid oil drip back down into the crankcase.

My guess - and I am no expert here - is that crankcase oil is making it's way out through the tube leading from the valve cover and into the intake (regardless if there is any kind of separator or not). That's what's fueling your runaway condition.

I don't understand why it would do this when the front of the car is lower. Maybe a high oil level is causing frothing up front, and that's making it's way into the valve cover area...?

Is the oil level on the high side? Perhaps overfilled?

Just some ideas.

- Patrick

junqueyardjim · #9 06-11-2005, 11:04 AM

Hi Diesel Benz; Twice now you have used the term "burning oil and sucking air" Again it is something that all diesel do well, when they are running, they are burning oil and sucking air, hopefully with a good air cleaner, nice clean air. But you mention "sucking air" in a negative way, like you don't like it. Why and please explain.

If it was easy everybody would do it

junqueyardjim

dieselBenz · #10 06-12-2005, 01:44 AM

By burning oil I mean...

crank case oil is being consumed at a rapid rate (~1 qt. in 200 mi.)

By sucking air I mean...

there is air in the fuel (bubbles can be seen in return line leaving fuel pump).

junqueyardjim · #11 06-12-2005, 03:59 PM

Hi Diesel Benz; I really don't want to be the one to pee on your parade. But Buddy, I think the answers to your problem should be pretty evident. I was hoping a couple of the big guns on this forum would come to your aid and say, Hey, hey, hey, you just got to do a little more tweaking here and there and that little old 240D will be as happy as a little old pig eating "grunt".
But life is life, and it ain't always easy. So to start lets look at this little paragraph.
"we rebuilt the engine ourselves so I haven't put much money into this car yet (that's how I like it).

But why did it start burning oil suddenly?"
That is why it is burning oil. You rebuilt it yourself and didn't put any money into it. What did you use for parts? Junkyard parts for an overhaul? Probably not. But here is what I suspect. A set of rings for all 5, any rod bearings at all, well maybe one or two looked bad enought to replace, borrow a ridge reamer and hack that ridge out of there, get the pistons (old) with new rings past what is left of the ridge and now use those two new gaskets, one for the top and one for the bottom, crank it together and you are very lucky it started up for you.
Then you mention two oil changes, one at 5000 miles and one at 10,000. Everyone on the forum is screaming, "change that oil and change it often" and they mean no more then 3000 miles. Don't tell me you had Mobil 1 in there. After doing a driveway overhaul you should have changed the oil at least at 500 miles and then again at 1000 or 1500.
But I suspect the damage was beginning as soon as you started it up and continues even now, at least when you run it. Take it apart and I think you will find broken rings, and broken cylinder ring "lands", that is the iron ridge between the rings. And probably scored walls and perhaps a broken piston or two.
But hey, don't give up on it. I haven't seen it and I don't know too much. If the car is as nice as you say, and if you don't want to spend the $2500 to $5000 for a total rebuild look around a bit and you just might find a good used one that could go a long ways. There are quite a few around.
But I think these engines are way past the point where anyone can remove the head and pan, slip on "some new rings" in the driveway or home shop. Our Grandpa's could do that with Henry's Model T and a few other vehicles of that era, but that will never work on modern engines, especially the diesel.
Again I hope that you can take some straight talk. I really like this forum for the information we can get. But we still have to work within our limits - tough limits of fit and finish, almost all tolerences at .0001 or 2 and some more stringent than that and cleanlyness that almost matches that of hospital surgery rooms. Thats tough to find on the driveway!

"If it was easy everybody would do it!"

Junqueyardjim

leathermang · #12 06-12-2005, 04:28 PM

"That doesn't seem to be the problem on my car.
I don't see the connection between the diaphram and sucking air (or burning oil!) anyhow."

So if you are not going to consider advise given by people with long histories of owning Mercedes Diesels....Why are you here ?
Paul's suggestion was very logical...
You don't own a factory shop manual for your MB do you ?

"After the rebuild, we changed the oil every 5,000 miles,"

I would have changed it at 100 miles, 500 miles, 1000 miles and 3,000 miles...
Were you using synthetic ? In that case you should not have used it until you had broken it in with regular oil....

What exactly did you do in the rebuild ? Did you set the bore to piston specs differently for number one piston ?

t walgamuth · #13 06-12-2005, 06:22 PM

i think you guys are being a little hard and judgmental here. this person has a problem and is hoping for help. if he has made mistakes perhaps he like most of us has a hard time faciing it and admitting it... but theres no reason to be nasty.

lets try to be positive. if he doesnt listen to our advice.... well we cant help him, but lets be as gentle as possible to someone who is down.

PatrickW · #14 06-13-2005, 07:08 PM

This is key, fellas:

Quote:

Originally Posted by dieselBenz

engine started speeding up by itself.

and this:

Quote:

Originally Posted by dieselBenz

without having the pedal depressed at all, the engine starts running faster by itself and blowing smoke.

1) Check your oil level. Is it high? Is it foamy?

2) Check for blowby.

I think you'll find one or the other.

Weather or not he changed the oil often enough, or used synthetic, or not - he rebuilt his engine. Maybe for the first time. We have to give him credit for doing that.

- Patrick

84300DT · #15 06-13-2005, 08:57 PM

maybe it's that negative pressure thing going on that another member had a while back? due to a restricted crankcase breather?