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Carbon build up is from oil flashing over as fumes and sticking to the valves. Using high flash point oil seems to eliminate this. One of our members has over 200K miles on his 335 and had his intake valves cleaned at 59K or close to that. He changed to high flash point oil and has never had to do them again. He also changed to lower OCI at around 7K miles. His is not a stock car either I believe he runs a JB4 tune.
I am curious about my intake valves and plan to pull my intake in Feb to replace the OFHG and see how bad my valves are too.
Subaru has a patent on their technique for DI engines which is reported to eliminate the carbon build up. I have not seem this problem reported much on the GM site for DI engines but significant reports on Audi/VW our BMWs.
Would be nice if BMW was not so mute on this topic because I think they know of a solution to the problem...
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