MB-JIM

Does anyone know what MBUSA position is on the potential for serious carbon buildup on intake valves with the new cgi engines? I have read horror stories of how this is a serious problem for other manufacturers of cgi engines. Is this something we will be able to prevent or will it simply be a non-warranty expense that we can look forward to?
I'm planning to buy a 2012 E350 but have some concerns if I'm buying into a reliability problem that doesn't yet have a solution.
Maybe someone from MB can give us some information to reassure us that it is not an issue with their engines. It would be irresponsible if they know there is a problem and we are going to let us suffer the consequences.

dariusf

I know my friend had this issue with his C a few years back but from what I understand it does not effect at least my engine.

dariusf

this is the response I got from MB dealer mechanic I know when I asked bout this in the past

Higgs Boson

not sure how cleaner in the gas tank will help, lol. the injectors spray straight into the cylinder, that's the issue... that won't clean the "top end" at all.

GoBlando

In the owner's manual it explicitly says to only purchase gas from the "Top Tier Gas" list found at TopTierGas.com. You may need to get the engine cleaned if you buy cheap gas. Worst case: a chunk of carbon breaks off and ends up in the catalytic converter. That is covered for 8yrs/80k miles by law in the US.

I had an Audi S5 that suffered greatly from this problem as I didn't know about the top tier gas list. I just thought putting 92+ octane in thinking that was enough. I was very wrong. Audi's design was bad because of the EGR system. A catchcan was supposed to be the work around.

Higgs Boson

A catch can assists in cleaning up the PCV system, not the EGR.

Wig

We've had the Mercedes direct injection engines for the 2012 model year, and half of the 2013 model year. We'd have heard of the horror stories by now if this was a real problem.

alsyli

I thought the problems w/ the BMWs and Audis didn't show up until around 40,000 mi? Might still be too early....

GoBlando

You are correct, but on the Audi forums, I am pretty sure Audi's design flaw was to pipe in the EGR past the PCV and directly into the intake using the assumption that the air had already gone through the PCV so no need to do it again. Since some engine oil could end up in the EGR, that is what causes the buildup. The idea for the S5 and RS4 was to install a catchcan between the EGR and Intake to try and reduce the amount of oil making into the intake. I do not know if Mercedes has this same problem.

Also, I never saw any threads complaining about carbon with the supercharged 3.0 for Audi. It was always the naturally aspirated direct injection engines.

Another note, besides bad gas, the only other thing that is really bad for the carbon buildup are short trips that don't allow the engine to reach operating temperature.

GoBlando

This is a cumulative problem as stated by someone else above. It wouldn't even show up in a 1 Million mile stress test because the causes of the problem are bad gas and short trips that don't allow the engine to warm up completely.

I had a chunk of carbon break off at 52k miles in my 08 S5. It destroyed two of the 4 catalytic converters. All handled under warranty and they properly cleaned the intake after replacement.

leapingpoint

Mercedes in china has this problem... But mainly due to the crappy quality gasoline...

mleskovar

Saw the 2012 in your sig.....did you buy one? What was the answer you received about the carbon build up? I'm curious too as despite the increased power and better gas mileage offered by the DI engines I've read the carbon buildup has been an issue. One guy dyno'd his car and showed a 10% in a year (forgot the mileage) reduction in hp due to buildup in his Audi. I talked my daughter out of buying an IS250 because of the reports of required intake track cleaning. I've also read that oil becomes contaminated quicker. I hope these are early life problems that have been solved and MB is ahead of the game.

thekurgan

Just about ALL direct injection engines will need this service eventually.

http://www.bgfueltest.com/

Some manufacturers like Subaru and Nissan have a port injector along with the direct injector; I'm not sure of the reasoning, but the port injector will alleviate the carbon build up.

This is a very interesting report by BG.

2006_C350

buy a Mercedes extended warranty...that's what I'm doing

mleskovar

I read an article by a manufacturer's engineer that said the reason is efficiency. He stated that at higher RPMs the intake injectors are more efficient and DI more efficient at low RPMs. An MB mechanic told me "we're running out of engine stands" when I asked him if it was a problem. He said due to the variable induction tracts they couldn't clean the intake in situ. BMW owners are walnut shell blasting their intake tracts for about $1K. They are also installing baffled catch cans to varying degrees of success. I can't imagine MB letting this become and issue without an easier solution, they'd go broke pulling motors.

thekurgan

Yes, it's for efficiency, but does have a cleaning side effect not planned. You are correct though, this is making engines more expensive in the long run to own and operate.