350 Oil Consumption - PeachParts Mercedes-Benz Forum

beaulieub · #1 08-10-2006, 08:18 PM

I've searched the archives and cant find the answer to this question - hoping you guys can answer it for me. If a 90 350SDL was burning oil as a result of the infamous rod-bending and the cylinder wall was ovalling, would the rate of consumption be constant no matter the driving conditions or speed? I'm seeing about 1 qt consumption in maybe 400 miles of various driving patterns - some light city trafic other 70 MPH highway stuff. However, when a few weeks back I did no driving greater than 55 MPH and travelled about 650 miles and only consumed 1/10 of a quart of oil. This is a new car for me so I have no info on previous consumption. It has 190K and runs beautifully and is fast for a diesel. Im hoping this irregular oil consumption means it at least isn't leading to rod-bending but maybe at high speeds the turbo is sucking the oil out or something similar. What do you think?
Also, Is an EGR valve the same as a PCV? Where is it located on this engine? I hear talk about a crossover pipe but dont know where/what it is.

Thanks in advance.

jshadows · #2 08-10-2006, 08:25 PM

can't answer your question directly, but check turbo too...bad oil seal will throw all kinds of oil back into engine. rather than back into the pan.

sixto · #3 08-10-2006, 08:41 PM

A leakdown test will help you determine if oil is coming up past the rings. A compression test will probably tell you as well since I don't think these engines bend all rods... and certainly not at the same rate.

PCV (positive crankcase ventilation) is not EGR (exhaust gas recirculation). The exhaust manifold has a corrugated pipe that feeds the EGR valve attached to the mixing pipe. That's the pipe that sits above the turbo compressor outlet and feeds the intake manifold.

The crossover pipe is the pipe that goes across the valve cover to bridge the turbo and the intake manifold.

Sixto
... stay tuned

Brian Carlton · #4 08-10-2006, 08:46 PM

My belief is that once the cylinder is ovalized, the rings are compromised and the engine will burn oil at a relatively steady rate. Sure, the consumption will rise with increasing crankcase pressure caused by oil passing the rings on all stokes but the power stroke. But, overall, the consumption is not going from 1 quart every 400 miles to 1 quart every 2000 miles by simply changing driving patterns.

My experience with the turbo also points to relatively steady oil consumption..........independent of driving patterns. The turbo is going to leak/consume oil based upon oil pressure and there is not much that is going to affect this unless you run the vehicle at idle.

The EGR valve is not the PCV. The valve is located on the passenger side of the engine.......close to the front. It has a corrugated steel tube extending from the bottom of the valve that attaches to a boss on the exhaust manifold.

The crossover pipe is exactly what it sounds like. The aluminum tube over the top of the valve cover that takes the compressed air from the turbo and dumps it into the manifold. Open the hood. It's the very first thing you'll notice.

sixto · #5 08-10-2006, 08:49 PM

Brian: "It has a corrugated steel tube extending from the bottom of the valve that attaches to a boss on the exhaust manifold."

Sixto: "The exhaust manifold has a corrugated pipe that feeds the EGR valve..."

Is this a chicken or the egg thing?

Sixto
... stay tuned

Brian Carlton · #6 08-10-2006, 09:01 PM

Quote:

Originally Posted by sixto

Brian: "It has a corrugated steel tube extending from the bottom of the valve that attaches to a boss on the exhaust manifold."

Sixto: "The exhaust manifold has a corrugated pipe that feeds the EGR valve..."

Is this a chicken or the egg thing?

Sixto
... stay tuned

.........did you backwards learn me that..................

beaulieub · #7 08-10-2006, 09:51 PM

So, does anyone have any explaination for the difference in oil consumption?

Brian Carlton · #8 08-10-2006, 10:43 PM

Quote:

Originally Posted by beaulieub

So, does anyone have any explaination for the difference in oil consumption?

I'll take a crack at it, but, admittedly I have no data.

At 55 mph, the engine can basically run without any boost.......just about zero manifold pressure/vacuum. The engine is lightly loaded and produces a certain amount of blowby, which has some oil in the stream, and it's burned in the engine.

At 70 mph, you're definitely into boost.......maybe 5 psi........and the engine is loaded to a greater degree.........and the blowby is increased. More oil goes to the turbo and is sent back to the engine for burning.

The difference is far greater than what I would have expected, but, if the data is accurate, it might be a decent theory to prove.

You can always run the hose from the top of the valve cover into a small bucket and see how much oil accumulates over a specific mileage. This would confirm or deny whether the cause of the consumption is blowby.

beaulieub · #9 08-11-2006, 12:40 AM

I read somewhere to put a copper T-Fitting into the hose from the valve cover and catch the oil. But I'm wondering if doing that would cause less oil to be sucked into the turbo because of the new opening into the catch bucket.

beaulieub · #10 08-11-2006, 01:00 AM

Also if oil is going into the turbo, wouldn't the crossover pipe be gunked? Would it be helpful to remove it and examine for oil? Seems like that might be easier than removing the turbo to look. Also, does this engine have a PCV and where would it be. I did find the EGR. Thanks

Blevinsax · #11 08-11-2006, 01:28 AM

I've read several times that it is advised to disconnect the EGR on the 350SD's and I'm curious about two things:

First - please explain why that is beneficial; I don't mean to question, just that I'm new to diesel/Mercedes, so I don't know that much.

Second - would someone please put a photo of the EGR valve so I can find it in my engine, too? I've read the descriptions, but as the old saying goes, "A picture is worth a thousand words!"

Oh yeah, and third - how would one go about disconnecting it???

Thank you very much!

sixto · #12 08-11-2006, 05:09 AM

The EGR system allows exhaust gas to flow into the intake stream. The mixture of hot sooty exhaust, crankcase vapors and as the car ages oil leaking past the turbo seals conspires to send goop through the intake manifold and into the cylinders. If you pull the crossover pipe you'll likely see 1/4" or more of oily soot on all internal surfaces.

So reason 1 for disabling the EGR system is to prevent this sooty build-up. Reason 2 is there is speculation that chunks of soot get into the cylinders. This soot is not very compressible so the connecting rods struggle to push the piston to top dead center and eventually yield.

To find the EGR valve, follow the crossover pipe from the intake side of the engine to the exhaust. It will bend down towards the mixing pipe which was an appendage bolted to it. The appendage is the EGR valve. You'll see a metal pipe with an accordion section leading to the intake manifold.

The methods of disabling the EGR valve include impeding the vacuum signal to the EGR valve canister and fitting a blocking plate between the EGR valve and mixing pipe. You can remove all the EGR components and plug all the holes, of course.

Sixto
... stay tuned

andmoon · #13 08-11-2006, 06:32 AM

EGR disablibg is not legal!
A BB or two falling into the vac. line is an unfortunate accident.
Make certaing the egr valve is not sticky if you are going the BB accident route.

sixto · #14 08-11-2006, 02:02 PM

Quote:

Originally Posted by andmoon

EGR disablibg is not legal!

That too

Sixto
... stay tuned

Brian Carlton · #15 08-11-2006, 02:22 PM

Quote:

Originally Posted by sixto

The methods of disabling the EGR valve include impeding the vacuum signal to the EGR valve canister and fitting a blocking plate between the EGR valve and mixing pipe. You can remove all the EGR components and plug all the holes, of course.

.........sometimes you can purchase a kit that removes the valve completely............for testing purposes only, of course..........