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2011 c300 smoking heavily out the exhaust when revved,

2011 c300 smoking heavily...

2011 c300 smoking heavily out the exhaust when revved

Mechanic's Assistant: How many miles are on the car? How has your mileage been lately?

102,614. I'm an auto technician by trade but have not seen this problem yet, someone said a failed intake gasket?

Mechanic's Assistant: Are you fixing your C300 yourself? What have you tried so far?

Yes I'll be doing the repair(s) but have not touched the car yet

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Not that I know of

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Answered in 17 minutes by:
10/3/2016
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,086
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello

The first thing I'd check is the crankcase pressure relief valve (PCV) these are sprung loaded and are only meant to 'burp' excess pressure every now and then. The exiting gas is piped back to the inlet, however should the valve stick open then the engine tends to suck the air out of the crankcase all the time and this carries oil over with it.

If you remove the air intake pipe and look inside where the crankcase breather is plumbed in you may find evidence of oil.

If you do find oil replace the valve

. If this is all OK then its possible that the valve stem seals are past their best and are drip-feeding oil into the intake. These can be replaced without removing the head by a competent garage in half a day or so

an engine flush may also help if you've got a sticking oil scraper ring so its worth a go, as for the oil if you go up a grade / use slightly thicker oil then this is less readily drawn into gaps and less likely to be burnt off

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Customer reply replied 1 year ago
I'll definitely check into those and hopefully that's what it is. Thanks for the quick response.

no problem

just get back to me on this post

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Customer reply replied 1 year ago
Haven't pulled the pcv centrifuge yet but it's got quite a bit of oily residue around it but I'm also seeing residual oil along the sides of the intake. Not soaked but just some seepage.

that does sound like the breather has been overloaded might be worth trying the oil flush to begin with

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Customer reply replied 1 year ago
Well so far you hit the nail on the head, the pcv is caked with old oil, very sludgy. Sadly, the folks I work for may not do the oil flush. But if they do, what's a good method to use, chemicals?

Hello

yes the flushing treatments are a chemical you add to the oil which then loosens off all the deposits

you then drain the contaminated oil off and replace the filter and fill with fresh

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Customer reply replied 1 year ago
Awesome thanks, I'll keep you posted

understood

Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,086
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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