HI
I have been concerned about carbon build-up on my XT since I heard of the problem but there does not appear to be any consistent data as to how to reduce it or if it will become a problem. I expect that Subaru is keeping quiet about what they know because it could reduce sales.
I have not heard this as actual fact.Can you give any references? I agree that most DI engines do accumulate carbon but the amount and impact on the performance or efficiency does not seem to be well documented. Is this actually a service that is on the recommended maintenance schedule? It does not appear here in Canada at least not for my 2015 XT. I have seen comments about some in Australia but little about the actual result of the work. The only effective method of cleaning carbon off seems to be walnut blasting and that is more expensive than $130 so far.Most all DI engines will have carbon buildup (except for those with dual port/DI) so every 30-45K you can choose to have a carbon service done for about $130 to clean off the valves...no biggie and it works very well. The Subaru dealer will do it to.
I have been concerned about carbon build-up on my XT since I heard of the problem but there does not appear to be any consistent data as to how to reduce it or if it will become a problem. I expect that Subaru is keeping quiet about what they know because it could reduce sales.