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!

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

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!

Do a search on :

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

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

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?

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

__________________
Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

This is key, fellas:
and this:

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

__________________
1982 240D. 198k, Marine Blue/Blue, 4 Speed, Crank Windows, No Sunroof, No Rust, No Oil Leaks
2001 TDI. 197k, Lagoon Blue/Black, 5 speed, Chip, G60/VR6

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

__________________
1984 300D Turbo - 231k....totalled 11/30/07 RIP

Your thread is a little old now. Just thought I would express an opinion. Since you are able to discern the base oil burning is heavier at sometimes than others it seems that piston, piston rings, valve guides etc. are not involved to any signifigant degree. I would first try to establish if blowby pressure is within normal limits. If blowby is really excessive though you have found your problem. On the newer engines if blowby starts to get into the dangerous area it shuts the pump down. Some people have thought this feature was accidental perhaps but I have thought it intentional design. If not examine any point base oil could be getting into the cylinders very carefully. Never owned one of these earlier blocks myself but mention is made of a diaphram on the injection pump. Suspect the guys mean if it is cracked base oil will be going to where it should not. Basically if blowby is not excessive again I cannot see the basic block being the causitive agent if problem is not constant. I tend to believe you are getting surges of base oil as at a burn rate of 200 miles per quart the engine would not be thought to be fuelling itself on a constant basis with the base oil. Just a few of my thoughts probably worthless.

"Do a search on :
Pneumatic governor diaphram. You may have to search back several years."
---Palangi (Paul )
--------------------------------------------------------------------------
"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."

"But why did it start burning oil suddenly? "----dieselBenz
==========================================================
"mention is made of a diaphram on the injection pump. "---Barry123400
---------------------------------------------------------------------------
Paul has owned these old blocks.... but dieselBenz dismissed that suggestion...

The vacuum pump on these models had a rubber diaphram. When it gets a hole in it, the vacuum produced sucks engine oil through, and it vents into the intake. Having the car pointed down at the front makes this worse, as the oil from the valve train runs down the front side of the chain case then. You can suck all the oil out of the engine and sieze it up if you don't watch it.

Easy fix, just remember to use the locktite on the center screw, or it will come out and pucture the diaphram again.

The air in the fuel is a leaking suction line. Cut it off and replace with a new hose. The old one is crimped on, I think, to a screw fitting. Common problem, and if not fixed will prevent starting eventually.

BTDT on both items.

Later vac pumps vent back into the crank case, and by 1980 or so were piston type rather than diaphram, so those models won't pull oil like that.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

it sounds as there is definately a problem other than faulty rebuild. there could be mistakes made in the rebuild that contributed, but this is not a common problem, i dont think. i am clueless but hoping someone with experience will pick up and help out.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

When you say "rebuilt"

What exactly was done to the motor- just to eliminate assumptions.


Michael

__________________
Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

I tried to get info on that earlier...

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