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Chris Haney 12-30-1999 07:36 PM

I have had my deisel about 6 months now. I had the oil tested for clues to engine performance and the tests show high soot levels after only 3500 miles between oil changes. I change the oil filter each time.

How about a quick lesson on soot? How does it get into the oil? Can it accumulate in the oil passages? Is there something that can be added to the oil to clean the crankcase etc?

VA300SD 12-30-1999 10:05 PM

Oil in diesels will look contaminated in no time after the change. Not unusual.
Most will suggest oil/filter changes every 3000 miles (or less), and then there is enough info for a PhD dissertation on oil selection.
I'm using 1-gallon jugs of Shell Rotella (because it can be bought cheap by the case at Sam's Club) and plan on changing the oil/filter every other month, irregardless of mileage, which will be far less them 3000 miles.

Not to start something here, but in most of my monitoring of posts on this subject matter the popular notion is diesels need to be run steady and hard for extended periods to keep things cleared out and the car happy. We use ours almost exclusively for hauling the kids to their grandparents an hour away via the interstate or for trips that involve several hours of driving.
If there is puttering around town on short trips, usually there is a trip down the interstate soon afterwards that helps clear things out.

Aaron 12-31-1999 12:03 AM


As VA300SD said, you do have to give the car a good hard run every so often to keep things cleaned out (i.e. carbon). I give my 300SD an "Italian tune-up" just about each time I get on the freeway with it, and when I travel back to Cleveland on the weekends from Cincinnati (about 250 miles), I will try to keep it at a constant 4,000rpm traffic permitting, that is. It doesn't hurt to use a bottle of Red Line Diesel Catalyst every now and then as well. I use Castrol GTX 10W-40 in all of my MBs, but tried Castrol RX Super 15W-40 in my 300SD on the last oil change. It is formulated for diesels and does meet Mercedes-Benz engine oil standards, but during this cold weather I think I am going to go back to GTX 10W-40. In addition, I notice that the car runs cooler with 10-40 in it versus the 15-40 on those hard highway blasts. Hope this helps!

Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'79 6.9
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8

Roger 12-31-1999 02:40 AM

So far the members have adroitly avoided your question about the soot. MBZ lovers seem more into oil changes and Italian tuneups. Lets get down to soot.

Diesel fuel produces much more carbon (soot) than similar amounts of gasoline when burned under similar conditions.

An origional German plot by one Herr Diesel uses heat resulting from very high compression to burn cheap stuff that spark plugs won't detonate, like most any flammable oil with a btu content above cotton seed oil (Crisco and Mazola Oil got me and my VW Rabbit Diesel home a few times in my "youth" when diesel pumps were scarce).

Note: MBZ requires conventional Diesel fuels if you want to get more than the 88k I got in the VW.

Anyway, Herr Diesel's technique results in an efficent, though rather nasty, combustion of cheap fuel with lots of soot left over. The essential high compression blows much of this soot past the pistons into the crankcase and garbages up the oil. This requires the mandatory use of the special motor oils rated for diesel engines like Aaron and VA300SD use and reccommend.

Diesel rated motor oils have the essential additives that will trap the soot, keep the engine clean, passages clear, keep smoke emissions down, etc. But one MUST change oil frequently. Each 3000 mi is good, unless you want 88K like I got on my first diesel.

I too recommend the Red Line fuel addative appropriate for your model engine.

240D 299K miles

[This message has been edited by Roger (edited 12-31-1999).]

JDEN 01-03-2000 08:08 PM

Roger is completely correct on this one. Only one other thing I might add is that because piston to cylinder wall clearances are, out of necessity, larger when the engine is cold, more combustion blowby will occur in a cold engine vs. a warm engine. If you use your diesel for short trip driving where the engine is never fully warmed up, you will load your oil much more heavily with soot than VA300SD will. Diesels are not the best choice for short trip drivers. If you fall into this category, you should consider changing your oil more frequently using a diesel service approved oil. Unmitigated soot loading causes oil thickening which in turn affects pumpability which in turn affects lubricity to critical engine parts.

Chris Ecklund 01-05-2000 12:43 AM

There is one thing left out in your original posting, you never said what kind of diesel you have!

If you have a 98 or 99 606 engine, the levels of soot will be much higher due to the new epa standards that they had to pass.

Not to get to techy into this subject(again), but if you do, or do not have one of the new diesels, use the new oils made for the 98 engines.

These oils have one massive improvement over the old ratings, and that is there ability to hold soot longer in suspension.

Please folks, dont get into this oil versus that one, just remeber the new ratings of CG and CH 4.

Chris Ecklund
98 300 DT

VA300SD 01-05-2000 03:14 AM

Did forget to mention my religious use of Redline fuel additive. It is used based more on conventional wisdom passed on to me from others then any scientific facts.
I carry several bottles in the trunk and use the recommended dosage with every fillup -
(1 bottle will treat 10 fillups of 20 gallons.)
I am not certain this will reduce soot contamination of the engine oil, however.

One more item of importance is regular valve adjustments (if the engine requires it, as is the case with the engines)
Just had mine done and the engine is purring at idle with the minor rocking completely eliminated.(Thank goodness it wasn't something with the injection pump.)
And the mechanic enjoyed the MB wrenches I loanded him, purchased at the Parts Shop.
Maybe I'm imagining this but there seems to be a reduction in exhaust belching as well.

I do agree that sticking with CG-4/CH-4 rating is a good idea irregardless of what brand oil is chosen.

Hope I didn't stray too far from the oil soot topic, but thought maybe smoke belching and oil soot may be related ? I'm not sure...

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