Does soot in the intake find its way into the engine oil?
 

On another thread, this issue came up...but I thought I'd create a thread that directly addresses the question.

Does soot that enters through the intake manifold, via a functioning EGR, contribute to the soot in the engine oil? From various sources, I thought the answer to this question was definitely "yes." However, at least one person with a lot more knowledge than I have says "no," at least not to any significant degree.

Any answers and explanations are appreciated. Thanks.

Maybe if the valves are not adjusted or not seating properly?

I think it's safe to say that nonfunctioning EGR valves do not contribute to soot in the crankcase. When in doubt, play safe.

That much I knew! :)

I would say that the answer is logically and technically "yes", but the actual amount is probably unmeasurable.

Soot comes from combustion and over time finds it's way into the engine oil. With an EGR system, there is an amount of combustion gasses that are recirculated into the intake and become part of the mix of soot that are created by combustion. So combustion soot + EGR soot is the new base amount of soot that can find its way into the engine oil.

So the real question becomes, how much EGR gas is introduced. I couldn't find an actual answer but one source suggested that it could be up to 50% at idle. I find that a bit hard to believe, but who knows. At cruise it's probably in the low single digits...maybe less.

No matter what the amount, as said before, it's best to just be safe and just recirculate the EGR gasses to the exhaust where they belong and not the intake where they are guaranteed to muck up your intake, reduce mileage and decrease the efficiency of the engine.

My opinion: sort of.

The purpose of the EGR is to reduce combustion temperatures to reduce NOX emmisions, to save the planet.

Reducing the combustion temperatures increases the amount of soot produced.

Said soot can then collect on the cylinder walls, and get washed into the oil system, and is removed when you change your oil. While it is suspended in the oil, it increases engine wear.

So, the soot that is already in the exhaust and is re-introduced to the combustion process probably also gets deposited onto the cylinder walls and thus enters the oil, and contributes to oil soot levels.

I think it's safe to say that you won't find any informed answers here. But logically and technically, the answer is "no". There's no path, direct or indirect, that EGR would increase the soot level in the engine oil. Anyone with real data, speak up, I can't see you if you just wave your hands.

Hmmmm, don't quite know how to read this...

Soot from the intake could go past the rings into the oil. As others noted I'd think the difference is minimal. Most all of the soot in the oil comes from "primary" combustion.

-J

And recirculated soot can burn up the second time around. It's all conjecture unless someone has a set of oil analyses.

Good point.

However, there is a period of time during the intake stroke when the intake charge air has the opportunity to deposit carbon soot on the cylinder walls, and said cylinder walls are subsequently covered by the piston/rings, and THAT soot is not going to be burned up in the combustion event.

I think it is pretty clear that the EGR is introducing exhaust gases which contain soot, and some of that soot is going to be deposited in the oil and increase the amount of soot in the oil.

Thanks for the responses thus far. I will say that one forum member has done multiple oil analyses on OM60x engines both before and after EGR deletion and found significant soot reduction.

My anecdotal experience coincides with this. The oil does not get black nearly as fast after an oil change on an engine that has been EGR bypassed.

See slide two of this presentation:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCgQFjAA&url=http%3A%2F%2Fwww1.eere.energy.gov%2Fvehic lesandfuels%2Fpdfs%2Fdeer_2008%2Fsession10%2Fdeer08_ajayi.pdf&ei=4ElMU86gMsf38AH184CwDA&usg=AFQjCNH0 goZ84AhmFLv4UmQ7PaUV-5zOBw&bvm=bv.64542518,d.b2U

Here is a less crazy link for that same presentation. See slide 2:
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2008/session10/deer08_ajayi.pdf