shashivr4

So my wife's Lexus IS is having some issues and the dealer is stating that it's experiencing carbon buildup due to the direct injection engine. Are they're any concerns with carbon buildup on our 2012+ 350s? If so, how can we stay proactive?

Thanks!

axhoaxho

I had a 2012 E350 (DI engine) for almost three years, and no issues at all. The engine started like new every morning, regardless of the weather. The engine felt just like the day we picked it up new at the dealer.

All we did was to use 'only' Chevron Premium gas (91 Octane in CA here) in every tank since it was new. We did the annual Service A and B at the dealer. That's all.

I don't know, may be we were lucky or Mercedes engineered the engine right...

Now we traded-in the E350 with a E550 (also DI), and we plan to do the same. Fingers crossed.

pdjv

I asked this question of a very knowledgeable M-B senior tech. The answer is that the engine design doesn't include anything (like EGR) that should/could lead to carbon build up in the intake.

GoBlando

I thought EGR systems are required by law in the US.

Arrie

I don't believe EGR valve has ever been required by law. It just used to be about the only way to "completely" burn the fuel by burning some of the exhaust gases again. It may also have helped with emissions this way.

Modern cars of today do a much better job with measuring the available oxygen in the engine cylinders and adjusting the amount of fuel sprayed in the cylinders accordingly.

dfordham

Albeit lengthy, this is an excellent thread concerning the engineering challenges inherent in the design of Direct Injection engines.

https://mbworld.org/forums/c-class-w...n-buildup.html

Regards,
Don

shashivr4

Thanks for the link! Very lengthy and informative discussion, but still unclear whether there's a known problem or not. Guess time will tell. Probably will buy the extended warranty just-in-case.

dfordham

These cars are very expensive to repair. If you are planning on keeping the car past the original warranty, getting an extended warranty is a good idea not just for potential DI problems.

Regards,
Don

mleskovar

A dealer MB tech told me "we're running out of engine stands to fix the carbon build up problem". All that could mean is it's more than one. I suspect usage has a lot to do with it. If....as the research shows (thanks Glyn)...it's from unburned gasoline backing up into the intake track and cooking on the hot surfaces then driving style will help minimize the problem. Avoid heavy throttle before the motor is warmed up to operating temperature and avoid WOT at low rpms unless necessary....or feeling the urge I'm guessing the latest US laws governing gasoline will help minimize this problem since it removes some of the contaminants in question.

pdjv

EGR is a solution for meeting emissions standards. A manufacturer that can meet emissions standards without resorting to EGR is money ahead. Apparently the new M-B direct injection engines are clean enough that EGR is no longer needed.

Arrie

This talk about carbon build up on the intake valves kind of does not make sense to me. The new engines don't have EGR meaning all air flowing thru the intake valves is just clean air. How in hell would these valves get carbon build up on them?

mleskovar

dfordham's link in post #6 explains it pretty well.....https://mbworld.org/forums/c-class-w...n-buildup.html Reader's digest version is the buildup is caused mainly by unburned gas entering the intake track from the cylinder and cooking on the hot surfaces.

GoBlando

The manual for my E550 specifically mentions using Top Tier Gas stations in the US to reduce the risk of carbon buildup.

C280 Sport

Carbon build up in cars come from not driving them. (My experience basically) I have never herd of a modern car however having these issues unless it sits for months at a time not used. Also too much light driving could cause a build up...Or am I thinking only in the days of old?

mleskovar

Yes.

alsyli

Interesting. I'm not at all technically minded, but I thought that Toyota's version of DI had some sort of combination of DI and multi-port injection to avoid the carbon build-up problem?

shashivr4

Same models do (I believe they call it dual injection). Unfortunately, not my wife's vehicle.

shashivr4

BTW, Lexus called today and stated they replaced the pistons and the rings. Apparently, all is well now.

mleskovar

The purpose of the Toyota direct/port injection combination is to increase gas mileage. As a side benefit it also solves the carbon buildup problem. DI is more efficient at low rpms and port is better at high rpms.

Arrie

And how does the unburned gas enter the intake track? I assume here it means unburned gas mixed in the exhaust fumes.

mleskovar

Valve timing/overlap and it's not just unburned gas left over after incomplete detonation. Some of it is fresh charge that escapes back through the intake valve before it completely closes.

Quadcammer

keep in mind that the cars should still have pcv valves which can cause the ingestion of oil into the intake tract without fuel to help clean the valves, you could end up with some carbon build up.