Black soot on rear - is it a gasoline issue

bobkat
4,825

Asked by bobkat Apr 09, 2013 at 08:11 AM about the Mercedes-Benz SL-Class

Question type: Maintenance & Repair

My car has 50k miles and runs great on mid-grade gas.. Lately I have noticed a black soot across the rear of the car. This would seem to indicate that the engine is not completely burning the gas. Does this mean that I should switch to a higher or lower octane of gas.? I usually use a Tier 1 gas - but not always. I ran regular for awhile and don't remember having the soot. Thanks.

28 Answers

judge_roy
Not Active

Mercedes often have soot on their rear. a yellow 1980's diesel comes to mind. Have you noticed a reduction in performance with the various grades of gasoline? perhaps your catalytic converter is not changing all the 2CO gas into CO2 effectively and leaving the residue that you're seeing, most likely is a catalytic converter inefficiency~

3 out of 3 people think this is helpful.
DavidH25
Not Active

Sure can not improve on that bobkat. I think he has it

2 out of 2 people think this is helpful.
judge_roy
Not Active

not bobkat goldwait?....well I'll be~

DavidH25
Not Active

...dipped......I finished your thought...

judge_roy
Not Active

That guy is a BRILLIANT comedian...very unique vocal stylings, does the guest voices, from time-to-time, like on the Simpsons, for example!~

judge_roy
Not Active

gotta pause for the cause, even tho maggie's dead now, cannot drink this pot of tea anymore....got to have a nice American drink....French roast~lol

bobkat
4,825

One last question - are catalytic converters one of those emission items covered long term by EPA warranties? Or should I just put the top the down, go cruising and forget about it. Thanks.

2 out of 2 people think this is helpful.
judge_roy
Not Active

is it really that terrible? you might want to think about a tune-up, retarded timing can make it more sooty, if you were running with a choked air filter, dirty plugs, retarded timing, defective PCV, and EGR valves could cause bad performance. NO spend some money take it for a tune-up and your black soot will be minimized~

3 out of 3 people think this is helpful.
DavidH25
Not Active

Yes they are. They fall in to that category. But for how long I don't know, you never said what year your car is? And ask away, ask as much as you want/need to know bobkat

3 out of 3 people think this is helpful.
bobkat
4,825

Thanks guys. Sometimes I get a little anal about perfection and worry about things that are really not that critical. Its 80 and sunny here - I am going to put the top down on my 2007 Sl and take the 'ponies' out for a ride. Thanks.

4 out of 4 people think this is helpful.
DavidH25
Not Active

you dawg you. It's 42 and windy at home here

1 out of 1 people think this is helpful.
judge_roy
Not Active

the EPA is okay...they make it so it's a lot harder to commit suicide with your car...all the carbon monoxide gas is changed to carbon dioxide gas and water- You could spend hours in a closed garage, and all you'd get is a headache~

1 out of 1 people think this is helpful.
judge_roy
Not Active

winter winds a bloooooowin; cold~

judge_roy
Not Active

thats you Kat you...is in florida or santa barbara?

bobkat
4,825

Central Florida - the land of Mickey Mouse

2 out of 2 people think this is helpful.
judge_roy
Not Active

the 'ponies' got horses there?, THE means of transportation before we decided that an above 30mph skull-splitting speed shall be the wave of the future~

DavidH25
Not Active

53 in Santa Barbara right now...and it's all the way up to 42 now but got to 27 last night, lawn is frosted still

DavidH25
Not Active

Really Judge? I did not know that.. and the EGR eliminates Nox. or better said greatly reduces...actually the EPA is one gov't bureaucracy that actually does some good. I can recall in the late 50's and 60's where I grew up there are 10,000 ft mountains, about 30 miles away from the old home, you could not see them. At all. Now, with all the bitching and shining people do about smog checks, I am all for them, there has not been a day in 30 years that when I go there, 'the place that when you go there they have to take you in" ..that I can not see those mountains. Air quality in the LA basin is so improved it's, well, wonderful.

judge_roy
Not Active

the air has a "snowball" scent to it today, like definitely droppin' down from the northern half following the jet in a counter-clockwise fashion.

judge_roy
Not Active

What's all this talking and fussing about Nitrogen? it is eighty percent of what we are breathing right now, is inoccous, doesn't react with anything very easily and we are swimming in a sea of it....these 'Nitro' kits Nitrous oxide....basically Oxygen so much hullabaloo about these cylinders to make it go even faster...

DavidH25
Not Active

yep it's just an oxidizer, hydrogen peroxide would go the same thing, it makes the fuel burn faster. they used it to launch the space shuttle, HP that is, that is what was in those big tanks strapped to the side

DavidH25
Not Active

Pure peroxide though, the stuff at the drug store is ..what..3%?

judge_roy
Not Active

Clearlake doesn't have drug stores anymore, not since the Walmart showed up in Lower Lake, but if they did would probably not feature anything that might be abused or used for ulterior possibilities~

judge_roy
Not Active

but they have no problem sellin' shotguns and ammo-

DavidH25
Not Active

That's the way of the world I guess now. Here you can not buy Sudafed without showing ID, sign a ledger, and you can only buy 2 boxes

judge_roy
Not Active

rather than find inner peace would rather find outer piece....terrible...sorry~

tenspeed
65,635

The "soot" may actually be the signs of an oil leak. When the cars moving, oil vapor floats out the back and deposits on the body. If it's soot it would be centered around the exhaust tips. If it's a leak, it would be more evenly spread across the rear.

1 out of 1 people think this is helpful.
garenad
305

if all the above did not solve your problem, check your head gasket then check and replace your oxygen sensors both upstream and downstream

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