Oil level high, is there a way to test if fuel is getting into oil? - PeachParts Mercedes-Benz Forum

nsiegel · #1 06-22-2008, 07:03 PM

I have an '83 300td.
I've been running it on biodiesel for the last year.
I've been noticing that the oil level seems high, and I am concerned that my fuel might be getting into my oil.
Is there any way to test for that?
For now, I am just keeping closer tabs on my oil level.

280EZRider · #2 06-22-2008, 07:16 PM

If the viscosity of the oil is what it should be, I would question the oil-in-fuel possibility. On the other hand, if there is water in the oil from a bad head gasket or cracked block, you won't see it by simply checking the oil via the dip stick.

My years ago, I had a similar situation in an old Renault, where the oil level appeared higher at each oil check. After finally removing the drain plug to investigate, about 2 quarts of water rushed out followed by the oil.

Jeremy5848 · #3 06-22-2008, 07:30 PM

If water is getting into the oil, you typically end up with a creamy white substance in the crankcase, which shows on the dipstick along with drops of condensed water when the engine is cold. Diesel (bio or otherwise) in the fuel will be harder to detect by eye but should also be less likely to occur because there really isn't a way (that I can think of) for fuel to leak into the oil in large quantities. A complete internal seal failure in the lift pump/IP is the only place I can think of.

In any case, you should also monitor your coolant -- are you having to add any? and your fuel mileage -- should be in the 20s for your vehicle.

There are labs for testing oil -- email George Murphy at Performance Analysis that I have used. They charge about $15, well worth it if you are concerned.

Jeremy

Jimmy Joe · #4 06-22-2008, 07:38 PM

Fuel dilution, as it is called, is a fairly not-uncommon significant problem in older motors that have internal hard fuel lines which can crack or otherwise leak. Though an unlikely scenario in a MBZ, nonetheless, should be ruled out if suspected. (ruptured diaphram at mechanical fuel pump, perhaps?)

In the bus industry, we regularly looked for the problem of "growing oil."
There are kits that can detect fuel in oil, but a simple way to guess is dripping a drop onto a paper towel (cold) and looking for concentric rings. The inner is solid black, oil, the outer is 'watery' in appearance, possible fuel.

You can sometimes smell fuel contamination. You can separate some in a glass jar, let it sit, and look for separation.

Best way is to send it in to get it analyzed. Cheapest way is change your oil and keep a close eye on levels.

Hatterasguy · #5 06-22-2008, 07:49 PM

I beleive the lift pump will leak fuel into the crankcase if it goes bad.

Palangi · #6 06-22-2008, 07:54 PM

Some years of TD's can leak leveling system hydraulic fluid into the oil. I don't remember if it was 123's or 124's that can have that problem.

sixto · #7 06-22-2008, 08:24 PM

123s. US 124s have an external SLS pump.

Sixto
87 300D

Jimmy Joe · #8 06-22-2008, 10:01 PM

i will add two things here; as I once let a fuel dilution problem go, until the friggin motor just froze, total bus trip disaster for everyone involved, and i've never quite slept the same after...

-these darn Mercedes are tough to get a good read on oil level. Mine is anywho. Are you certain you are growing oil? How do you ensure quality readings?

-if you do have the dreaded dilution, keeping the oil clean is paramount to your motor's survival. Change that oil until you find the problem/peace of mind!!! Clean oil will never kill a motor!

I guess what I am saying is: don't be paranoid, but you may well be onto something. As long as that oil is somewhat clean, it will continue to lubricate your engine.

JHZR2 · #9 06-22-2008, 10:14 PM

used oil analysis will tell you real quick... it will provide you a percentage dilution as well as a viscosity number. Since it will give you wear values, it will show the implication of the dilution, if there is one.

Get a kit here: OAI Oil Analyzers Inc. UOA Kits

And report the numbers back for me to look at.

best,

JMH

minimike1 · #10 06-22-2008, 10:15 PM

you might try putting a few quarts of ATF or Marvel mystery oil in the fuel and see if there's enough 'red' color in the clear prefilter to help you id the possible mix in the oil.

JHZR2 · #11 06-22-2008, 10:21 PM

huh??? it might make the fuel reddish, but the diesel oil is soot laden, it is effectively black ink in a heavy solvent!

No way youll see a bit of red in there, unless it is a LOT of dilution.

JMH

Diesel911 · #12 06-22-2008, 10:21 PM

Quote:

Originally Posted by Hatterasguy

I beleive the lift pump will leak fuel into the crankcase if it goes bad.

There is a tiny O-ring in a recess that seals the rod that pushes the supply pump piston. Besides this the piston runs metal to metal with no seal and if the pistion or the walls the pistion rides in gets scoured the pressure gets pushed on the tiny O-ring.

Cervan · #13 06-22-2008, 10:27 PM

the lift pump has a diaphram that pushes the fuel up and through the IP, if that cracks or goes bad you will have fuel in the oil. if your oil level is rising you should beable to smell or even taste it in the oil.

Jimmy Joe · #14 06-22-2008, 10:36 PM

Quote:

Originally Posted by Cervan

if your oil level is rising you should be able to smell or even taste it in the oil.

Ha!! A wise 'ole hippy told me that once, and there we were, side of the road, my co-driver sticking that dipstick in his kisser, with sad grimace on face, hoping to taste that diesel. But the rascal didn't taste diesel. We had major fuel dilution, yet continued unawares, t'was only an hour or so later the beast just froze as result of our negligence...

such a painful thing, we had nearly completed a cross-country loop, the final stretch is was; and you kind of fall in love with a bus like that after such an excursion... her name was Sammy... sniff...

Cervan · #15 06-22-2008, 11:03 PM

Quote:

Originally Posted by Jimmy Joe

Ha!! A wise 'ole hippy told me that once, and there we were, side of the road, my co-driver sticking that dipstick in his kisser, with sad grimace on face, hoping to taste that diesel. But the rascal didn't taste diesel. We had major fuel dilution, yet continued unawares, t'was only an hour or so later the beast just froze as result of our negligence...

such a painful thing, we had nearly completed a cross-country loop, the final stretch is was; and you kind of fall in love with a bus like that after such an excursion... her name was Sammy... sniff...

haha, maybie hes just never tasted diesel before? XD Sorry to hear that man.