[flybywire]

My 335d is coming up on oil change at 35k. Did the research and found that there's only one oil in the US spec'd for this car (LL-04).

Is it possible that dealers and 3rd party mechanics who don't understand diesels are using the wrong oil, and contributing to CBU via ash coming from oil?

[natefank]

Well I'd like to update mine and say that I think I'll be having CBU issues here pretty soon. I haven't gotten any SES lights or codes yet but its starting to idle real rough. I'm at 84,000 miles, I'm hoping it throws a code soon so I can get it taken care of before my CPO runs out

[Novo777]

So in reality it's not if but when CBU will be the problem!

[natefank]

Sounds like it to me, I drive my car hard and in DS all the time to try to not have the CBU but looks like it didn't work...

[Thecastle]

I bought a used 2011 335d that had cbu cleaning performed by bmw at 22k miles then promptly had a manufacturer buy back. So I got a great deal on a low mileage bmw that is carbon free... But I will do an egr block and probably replace the pcv. Cbu is a big issue on nearly all direct injection vehicles as the fuel detergents never come in contact with the intake tract to clean carbon build up.

If this issue is anything like the vws I've owned that suffered from carbon build up, fuel quality has probably nothing to do with it. As unburnt fuel never enters the intake tract on a direct injection engine. Yes, gasoline engines have egr as well

Source of carbon are egr, pcv and oil leaking past the turbo and valve stem seals. It's not possible to eliminate all sources of carbon build up but it is possible to slow it down. The only car compaines I've seen that have really solved this issue use materials on the intake that don't allow carbon to adhere to them, or have an injector in the intake tract to inject fuel to clean it (at least on gasoline vehicles)

[torqueisking]

43K miles on my 335d, 78K miles on my X5 35D without CBU...before I deleted the EGR. Hopefully I'll never have a CBU issue