What is blow by? - PeachParts Mercedes-Benz Forum

jgumina · #1 06-21-2009, 04:23 PM

Interested if blow by is engine oil going out the exhaust or something else?

How do I know if my 220D is doing this?

Why is there so much black smoke coming out of the tail pipe when I step on the gas? Is that blow by?

How long should the car warm up in the morning?

Matt L · #2 06-21-2009, 04:29 PM

Blow-by is combustion gasses going past the rings and into the crankcase. They typically get reintroduced into the intake to be burned again. In particular, blow-by gasses do not go directly to the exhaust system.

Black smoke means too much fuel is being injected. It could be because your compression is low and you can't burn as much as when the engine was new. It could be other things.

JEBalles · #3 06-21-2009, 08:26 PM

You can check blow-by by taking the oil filler cap off while the engine is running and place it over the opening. A general rule of thumb is if it stays put, blow-by is insignificant, if the cap gets blown of or moves around a lot, you've got low compression somewhere (which apparently causes lower combustion). Also, blue smoke means oil is being burned, not black.

jgumina · #4 06-21-2009, 10:23 PM

The smoke is black for sure, not blue.

Does thicker oil such as 20w50 work better than the 15w40 I put in it today?

Will perform the filler cap check.

Palangi · #5 06-21-2009, 10:32 PM

Could be 20 years worth of soot in the exhaust system.

JEBalles · #6 06-22-2009, 10:25 AM

Quote:

Originally Posted by jgumina

The smoke is black for sure, not blue.

Does thicker oil such as 20w50 work better than the 15w40 I put in it today?

Will perform the filler cap check.

What do you mean work better? Lubricate better? I'm not an oil expert, and if you aren't either, it's probably best to use what it says in the owners manual, that's what I use. I can tell you that a thicker oil could make it harder to start, depending on your climate, because it takes energy more to turn the crank in the thicker oil, but I'm not sure what kind of answer you're looking for with that question.

Brian Carlton · #7 06-22-2009, 11:10 AM