Blow by, black oil, doubt and confusion - PeachParts Mercedes-Benz Forum

gomerbarkley · #1 07-29-2008, 10:44 AM

My first post. . .

I just changed the oil then drove it ~20mi. and checked it. The dip stick said I put in too much, so I pumped some back out. I noticed that it was very black - yuck. I've removed the oil cap while running and noted the puffing associated with blow by. Would this cause the black oil? Is this soot in the oil or is the oil getting burnt?

The car starts and seems to run pretty well - should I test the compression? Any recommendations for a good (value) tester? Is there a DIY How-to for doing this test (please post link)?

Finally, if I do find a problem with the compression, what is the fix? Do I have to remove/replace the piston rings? Hone the cylinders? Can this be done with engine in or does this require pulling engine and all?

Thanks!

GomerBarkley
'82 300 D with 136,000 mi. purchased 2 months ago

vstech · #2 07-29-2008, 10:56 AM

black oil is instantaneous. unless you flush your oil cooler, wash out the entire inside of your engine, and install a full flow oil scrubber, your oil will always be black as ink in the first mile of driving... totally normal.
how much oil did you put in? should be 6.5 to 7.5 quarts depending on where you want the level to be on the stick. assuming you did change the oil filter before you finished draining the oil pan.
Harbor freight is a great place for low priced (cheap) compression tester.
Welcome to the forum!
check out www.dieselgiant.com on his link for mercedes repair... awesome!

LUVMBDiesels · #3 07-29-2008, 11:09 AM

Totally normal unless you do back to back oil changes and run on B100. I ran the SDL on B100 for about a week before it turned the new Mobil1 completely black

gomerbarkley · #4 07-29-2008, 11:26 AM

Thanks for the help! I've ordered my compression tester (only $30 with shipping) from Harbor freight. It'll help me sleep better to know; I'll post the results. I'm planning to replace the injector nozzles anyway, that'll be a good time to do it I think.

I'm glad to find out that black oil is normal. I was really worried. You guys are great.

Thanks!

GomerBarkley
'82 300 D with 136,000 mi. purchased 2 months ago

charmalu · #5 07-29-2008, 12:01 PM

82 300D with 136000 miles? wonder if that is correct? If it is you should show some good numbers on the compression.
be sure to post your numbers.

yeah black oil is normal, the older the engine, the sooner it gets black.

MY Metric Motor engine I installed a yr ago only has 8500 miles on it so far. and 2300 miles since the last oil change. it takes longer for the oil to darken up. right now mine is a light chocolate brown.

and as said above, the new oil mixes with what can`t be drained and blackens up soon.

Charlie

pawoSD · #6 07-29-2008, 12:04 PM

The oil on our cars turns black in about 3-5 minutes of starting the car.

Totally normal.....just an old diesel thing.

SD Blue · #7 07-29-2008, 01:27 PM

Just ensure to refill with a diesel-rated oil (CF,etc.)

hoborobot69 · #8 07-29-2008, 01:57 PM

I read or heard somewhere that before an oil change to add less than a quart tranny fluid to the oil and to drive with it for fifty or so miles at running temps then drain to clean out more gunk. I also seem to remember reading/ hearing to drain the oil, and replace all of it with tranny fluid and then let the engine idle without applying ANY load, to let it reach running temps, then drain, change filter and refill the oil.

Sounds like a pretty Podunk practice.. Anyone done this?

vstech · #9 07-29-2008, 02:02 PM

it used to be standard recommendation... it's not a good idea.
if you have a gunked up motor, it's best to use standard dino oil and change every 1500 miles with a new filter. this will get the detergents in the new oil working well, and keep the gunk from causing problems.

bgkast · #10 07-29-2008, 02:49 PM

Just run synthetic oil, it will clean the engine right up!

Thecorrupterx · #11 07-29-2008, 03:07 PM

^^^ What bgkast said, I picked up some Mobil 1 full synth turbo diesel truck oil and it actually stayed somewhat transparent for 3 weeks!! also it was my second change with full synth and about 5000 miles on the old oil, I changed it because it finally turned jet black.

Cr from Texas · #12 07-29-2008, 03:40 PM

I hate to toss the gunlet but I've got to ask:
Black oil is from suspended soot and the soot formation is the nature of the diesel combustion process, right? If so, if the oil is less black, where is the soot? Seems to me that the blacker the oil (same mileage) the more soot is suspended and removed when the oil is changed. That seems backward to the thinking of others - straighten me out.

hoborobot69 · #13 07-29-2008, 05:32 PM

any reason why it's bad to run the tranny method? Detergent varnishing valve train??? Or something similar?

SD Blue · #14 07-29-2008, 11:25 PM

Quote:

Originally Posted by hoborobot69

any reason why it's bad to run the tranny method? Detergent varnishing valve train??? Or something similar?

My thinking is, this is similar to using that motor flush product. The kicker is....how do you get the remaining flush (tranny fluid) out of the engine without doing back-to back-oil changes. Even then, you probably are just minimizing it's dilution effect on the new oil. What you end up with is partially diluted oil with unknown additive effects and questionable properties.

I know there is a deep down desire to have honey-colored oil but I don't believe flushing is the way to accomplish this. Some folks have tried additional bypass filtering even though it is fairly expensive for non-commercial use.

pawoSD · #15 07-29-2008, 11:27 PM

Putting something like transmission fluid in a place where it doesn't belong (mixed into engine oil) is only asking for problems. Stuff like that is never a good idea. Oil is for engines...trans fluid is for trannys.....they need to stay in their respective places.