240D engine question - PeachParts Mercedes-Benz Forum

#1 09-24-2007, 09:54 PM

I have a late model 240 diesel, and my question is this. At trips on the highway at above 65 mph for like a 400 mile round trip. It will suck the oil out. If you drive it around town it is like very little oil consumption. It doesn't have many miles on the car in my estimation. Like around 100K or a bit less. I know from articles that valve stem seals are not the culprit on this motor. As I did replace them to no avail. My wonderment is will valve guides help this motor or not? I wouldn't mind fixing the head with new quides etc. if that would eliminate it. I definitely do not want to do a total engine rebuild on this MB. Also, I am curious to find out if this motor did use oil or not when driven hard?? Any feedback would help, and any other suggestions. Sometimes I wonder if it might be something else causing the problem.

Cervan · #2 09-24-2007, 10:44 PM

headgasket, valve journals, rings... thats pretty much it...

t walgamuth · #3 09-24-2007, 10:50 PM

At lunch the other day one of my cronies stated that gasoline had lubricating properties that prolonged engine life (like diesel only less).

I said so then propane would wear an engine out sooner?

He said no but methane would.

Anybody know if this has any truth to it?

Tom W

lietuviai · #4 09-24-2007, 10:50 PM

Perhaps something simple like a clogged oil breather pipe or a dirty air filter?

t walgamuth · #5 09-24-2007, 10:51 PM

What are you burning in it?

What oil do you have in the crankcase?

Tom W

Stevo · #6 09-24-2007, 10:58 PM

Valve stem seals are usually not a problem with these engines because they dont make "vacuum" like a gasser.

#7 09-25-2007, 06:31 AM

I am using Mobil 1 5W-40 Turbo-Diesel Truck full synthetic motor oil. However, the book shows 10W-40 year around motor oil, that came with the car.

#8 09-25-2007, 06:39 AM

Quote:

Originally Posted by t walgamuth

At lunch the other day one of my cronies stated that gasoline had lubricating properties that prolonged engine life (like diesel only less).

Gasoline is a solvent, it has almost no lubrication. One of the bad things that happens when a gas engine runs rich is that the gas will wash the oil off the walls.

t walgamuth · #9 09-25-2007, 09:36 AM

thanks, I thought i was starting a new thread.

sorry for the hijack.

tom

to the op, if it is using a lot of oil I would go to a dino oil as thick as possible. like a rotella straight 30.

Tom W

JimSmith · #10 09-25-2007, 09:44 AM

By design this engine should hardly see any vacuum in the intake manifold. But, as noted earlier, if the intake air cleaner is clogged, the higher the demand for air (such as at higher rpm), the manifold vacuum will increase.

Another peculiarity for this engine is the vacuum pump arrangement. On some cars it discharges to the intake manifold, and if vacuum increases when it develops an internal leak, it will suck the oil out through the vacuum pump. Later models might not have had this feature, as the vacuum pump went through a series of design changes.

Same with the crankcase ventilation system. It vents from the top of the valve cover over to a cyclone separator mounted on the intake manifold. The non-condensable gasses are supposed to be stripped from the oil droplets there, with the oil droplets draining back to the sump and the gasses (blow-by, for the most part) going to the intake to be "recycled." Once again, a clogged intake manifold and you can see high enough vacuum at high speeds to suck all the oil droplets into the intake manifold.

Seems clogged intake manifold is a common theme above. I would take the air cleaner housing off and examine the intake manifold as well as air cleaner. You may have had a rodent decide the place was home if the car sat for any length of time.

Any signs of oil leaks? I have had some issues with rear crank seals on these cars, as well as one of the power steering or air conditioning mount support bracket bolts. It got loose and let oil spew out the front of the engine. I was sure it was the front cranks seal, and it turned out to be a bolt that cost me a steam cleaning and a buck.

Also, at higher speeds these engines use more oil, but not a quart in 400 miles. That is excessive. You are pumping oil somewhere you don't want it.

As for gasoline as a lubricant, all things are relative. In ship propulsion shaft bearings, sea water is used as a lubricant. In its liquid, pressurized condition, such as in a fuel pump, gasoline can be used as a coolant and lubricant (it can generate a hydrodynamic film), but as a spray on material it is going to evaporate and leave behind whatever additives are in the mix. Those items may or may not be slippery. I imagine not. And anything designed to be lubricated by an oil will die a quick death if you substitute gasoline.

Jim

Lycoming-8 · #11 09-25-2007, 11:14 PM

Yeah, the perfect exampe of that is the use of plain gasoline in a 2-cycle lawn mower engine like the older Lawn Boy. It will burn up the engine quite quickly; but with the correct amount of oil added to the gasoline, they will run for a long time!!