Diesel Fuel in Crankcase Oil- ULSD culprit? - PeachParts Mercedes-Benz Forum

willrev · #1 05-04-2007, 08:40 PM

Stopped for fuel today. Checked the oil. I recently did an oil change and the oil was fine then (3 weeks ago). I could not see much oil on my dipstick. Noticed funny smell. Oil was thin and running off dipstick. It was diesel. Called a towtruck.

I have 295,000 miles on the 1982 300sd. I maintain it meticulously. What has failed?

Has ULSD caused this failure? I found this article about ULSD causing lots of fuel-related failures on many makes of diesel engines on the throttle-shaft O-rings and gaskets made with a rubber compound. Some seals are failing within 3 weeks of exposure to ULSD fuel.

http://www.mbm.net.au/b100/lsd.html

aklim · #2 05-04-2007, 08:42 PM

How is your compression?

F18 · #3 05-04-2007, 08:55 PM

I think Aklim hit it right on the head. Fuel only enters your engine through your injectors. For it to reach your oil it has to pass by the piston rings......which means bad compression on one or two cylinders....some piston rings are worn. It has nothing to do with ULSD.

babymog · #4 05-04-2007, 09:07 PM

Can't it also get in through a failure of the fuel boost pump?

At 295k miles, thngs fail. By the time my 4matic had 100,000miles, I had the seals on the transfer case replaced twice, no ULSD in there. I had the oil level sensor leak on my 190D this winter, no ULSD there. Power steering leaks in one of my 300Ds, and I've had an aux-pump seep/leak recently also.

Although it is understood that older seals that have lost thier elasticity mignt not seal well and therefore might leak with the lower aeromatic content (= less seal swell) of ULSD, it is the age and lack of elasticity of the seal that causes the leak. Considering that most of the road diesel in the US has been ULSD since June of '06, the number of failures have been reasonably low. ULSD seems to be the scapegoat for all seal failures. Stuff wears out.

Good catch, good you caught it and had it towed. If the crankcase fills enough for the fuel to hit the crank the engine will go into runaway, your only hope of stopping the engine then is to stall it to a low enough RPM to keep the fuel from slinging onto the cylinder walls so it will shut down. Been there with a 10.4liter Cat diesel, it ain't pretty.

F18 · #5 05-04-2007, 09:40 PM

Jeff....you lost me....."fuel boost pump"? You have a mechanical Injection pump that has a O Ring seal on its drive shaft end where it connects into the crankcase and you have a low pressure fuel pump that is mounted to the side of the IP on this model that also has a traditional gasket. I suppose you could have a defective Injection pump that is blowing fuel by the valve seals and bearings and the crankcase mounting seal into the crankcase. But I think it would do this with an obvious change in the starting and running of the engine. It would definitly effect the fuel delivery pressure to the injectors.
It might be worth investigating.........Just thinking out loud while watching Star Gate and sipping a Rattler Martini

Gin, Vermouth & Orange Juice with pulp!

willrev · #6 05-04-2007, 09:40 PM

Compression has not been an issue for me. It starts up well. My last valve adjustment proved the timing chain was tight with little stretch.

All 5 injectors have been replaced a year ago with BOSCH factory rebuilt injectors.

Are there any seals than can cause this type of failure?

willrev · #7 05-04-2007, 09:42 PM

If this is a serious engine failure, do any of you know a reliable source for rebuilt engines. I have seen them in Adsit. Any others?

#8 05-04-2007, 11:52 PM

Quote:

Originally Posted by willrev

If this is a serious engine failure, do any of you know a reliable source for rebuilt engines. I have seen them in Adsit. Any others?

Adsit has a spotty reputation for customer service. AFAIK, metric motors is about the best:

http://www.mercedesengines.net/products.asp?cat=40

barry123400 · #9 05-05-2007, 11:07 PM

Before even considering the engine a cross contamination issue might be the lift pump as it is driven by the crankshaft in the injection pump. It should be removed and critically inspected or rebuilt or replaced with a used one. Next on my list would be the injector pump itself somehow leaking fuel into it"s base area. The engine itself would be my last suspect. I suspect the lift pump is also the strongest possibility. Fuel in the combustion chamber is going to get burnt well before it has time to get past the top ring unless that cylinder is not firing. You said the engine runs pretty well so that pretty well kills that.

Cervan · #10 05-06-2007, 01:51 AM

i would take out the lift pump and replace it. diesel fuel in the crankcase will copper the bearings very quickly.

Ken300D · #11 05-06-2007, 08:00 AM

There is a mechanical fuel pump on the driver's side of the crankcase, near the primer pump. It has the purpose of pushing fuel up to the cannister fuel filter and onward to the injection pump. It is powered by an elliptical lobe on the crankshaft, and that side of the pump is lubricated by engine oil. The other side of the pump, of course, pumps diesel fuel. If the integrity of the seal between these two sides of the fuel pump fails, then one side can leak into the other.

The oil is not under much pressure in this section of the engine. There's only the air pressure associated with blowby. The fuel pressure on the pressurized side of the fuel pump is more than enough to push into the crankcase, if there's a leak.

This is for sure the first place to look. Chances are that the leak has been going on for some time, but you may not have destroyed the engine just yet. If this is the first time you have noticed the engine above where you filled it with oil, then you may have caught the problem in time. The dilution of the engine oil may not have been significant until the time you observed the overfill.

If it were mine, I'd replace the fuel pump, engine oil, filter and try it again.

Ken300D

Carfax is $25 for 30 days - Autocheck is $25 for 60 days. Which is better for screening cars on EBay - are you better off with 30 days of screening or 60 days?

Alastair · #12 05-06-2007, 09:41 AM

There are only two ways that diesel fuel can get into the lube-oil associated with the injection-pump.

The first and very much likely, is from the Lift-pump bolted to the side of the lower case of the Injection-pump. This is 'driven' by an offset-cam on the Injection-pump cam-shaft. The lower 'cam-case' of the Injection-pump is lubricated by lube-oil from the motor. When the Lift-pump wears, it leaks fuel into the I.P lower-case, and gets into the lube-oil.

A much less likely leak can happen where the high-pressure elements wear and leak down into the 'tappet-chest' portion, and from there, into the lower-cam-case of the IP. This is much less likely, as when the elements wear to That extent, usually the engine is incredibly difficult to start, as the elements just wont make delivery pressure during starting...

As has been said, especially on a high-miler, just replace the Lift-pump, change lube-oil and filters. Above all, Keep a close eye on the lube-level over a month or so, after to confirm the fault has cleared by changing the lift-pump....

aklim · #13 05-06-2007, 09:44 AM

If you replace the lift pump, you might be throwing good money after bad if the cylinders are worn. First thing would be to do a compression test and see where it stands especially with that kind of miles, IMO.

willrev · #14 05-06-2007, 04:23 PM

I think I will see about replacing the lift pump and selling it. Again, COMPRESSION IS NOT AN ISSUE ON THIS CAR.

This car starts well in the dead of winter! I have a compression tester. Yes, it consumes some oil, but not that badly. It runs like a scalded dog as we say in the South! If this repair is $1000 or more either the car is sold to the junk yard or for parts. It has new Bilsteins, new rotors, new calipers, the rims have been redone. It has a perfect interrior, it has a new alternator, new injectors, new belts, a new climate control unit and a new Mercedes battery. It is a daily driver.

How much is a parts car worth?

willrev · #15 05-06-2007, 04:36 PM

I believe each of you has helped me solve the problem. I did a google seach on diesel lift pumps and guess what!

A major school system also report major failures in diesel lift pumps from switching to ULSD diesel fuel. I believe we have diagnose the problem. I await the mechanic's report tomorrow.

See this link:
http://www.southeastdiesel.org/Photos/FAPT%20ULSD.ppt

Another Link from Cummins on repairs - this says nitrile gasket is to blame:
http://www.blueridgediesel.com/CUMMINS%20TSB_082905%5B1%5D.pdf