Finally! The answer I was waiting for. No sense in cleaning the intake valves until there is an actual problem. If it was necessary it would be listed in Warranty & Maintenance manual.

 

Perhaps the difference between borescope use and 'feel good' application is more definitive.

 

Proof is in the pudding!
Only true way to tell is by a borescope inspection or by engine performance.

Preventative measures MAY delay the POSSIBLE need for valve deposit cleaning, but no one has done a comparison with an actual control vehicle and a vehicle that used "xyz" method to prevent it.

Lots has to to do with your driving habits and how often you change out that dirty oil. Other than that...its a gamble.

Let the debate and opinions begin

 

Which is why put a little PI in the gas with every fill-up and change Amsoil Signature engine oil every 6k miles. My antique Olds is my daily driver and gets all the short trip driving. The Trailhawk gets the long trips and off road workout.

 

Adding anything to gas is like using a rectal douche when you have nasal congestion. Laudable effort, but the liquid doesn't get there.

In our DI engines, fuel does NOT come into contact with intake valves, so you could flood your gas with any detergent on the planet, it won't change anything. Regular oil maintenance is more likely to help, but even then it's more a generic maintenance tip than a valve-specific preventive measure.

 

Short trips + a lot of idle will cake the intake valves faster, drivers who mostly drive on highways are less likely to experience issues with carbon buildup.

 

The "idocars" guy Eric, always finds a significant difference between a GDI and PFI when he tears engines apart, but not sure how that really affects real world performance.

 

Some people install catch cans, while others spray GDI cleaners, but I'm too lazy to do all that just to prevent something that may never happen. Maybe when I hit 50K miles, I'll take a look at the valves with a borescope just to see how they’re holding up.

 

When I had my XV I did the CRC every 7K miles. On my '18 Forester XT I do the same. I also had the dealer do it.

 

Maybe your approach is better, and 50K might be a bit late. I found this on a Forester forum: FA20DIT with only 35K km (22K miles).

 

Something seems off. I doubt all Subaru owners are following this decarbonization maintenance at the same time, especially considering how many Subarus are on the road. I sincerely doubt it's because they all have carbon issues at 50-60K miles. The majority of the owners probably have no idea what GDI means or how it works.

 

Something seems off. I doubt all Subaru owners are following this decarbonization maintenance at the same time, especially considering how many Subarus are on the road.

2017 below is non gdi engines

 

i think what many people dont realize when they use PEA cleaner is it takes time to soak and get good result, so when they do boroscope just before and after spray, it may not give much difference.
the pea cleaner works like typical oven cleaner, the longer the cleaner touches the carbon, the result is better. that is the reason I always put pea cleaner in fuel tank and run a few days before spraying it through intake tract and leave it for few hours before starting the engine, and continue to use it or catalytic cleaner for another 1 tank.

 

The only solution I see is to remove the intake, turn the crankshaft to close the valves, and then cover the valves with solvent for a while before mechanically removing the carbon.
Spraying cleaners through the intake doesn’t seem to work well, at least based on the 'before and after' videos I’ve found. Another concern is that the mixture of solvent and deposits ends up in the combustion chamber, which can shorten the lifespan of spark plugs and O2 sensors. Additionally, hard carbon pieces can easily scratch the cylinder walls. Starting to spray early, before every oil change, might help, but it’s kind of annoying.

 

At my age, life is too short to worry about, or take preemptive action to prevent, intake valve deposits that may or may not occur -- until/unless I'm starting to see a performance issue. It's seems a bit like checking and adjusting your tire pressures before EVERY drive, to prevent the (remote?) possibility of wrecking the AWD system because all your tires aren't dead-nuts equal. Please.

I'm guessing that the overwhelming majority of Subaru owners are neither mechanics nor mechanical engineers, don't follow this Forum, and don't lose sleep worrying about either "issue." Otherwise they might start thinking "buy another Subaru next time around? I don't think so?" In fact, Subaru continues to rate pretty high customer satisfaction and loyalty, across a broad spectrum of ownership experiences. Heck, I'm tempted to buy another Crosstrek, my current experience having been so positive (so far).

Having said all that, I value the expertise available on this Forum (really, I do), and find that keeping up with the postings enhances my ownership experience. Thanks to all you experts out there.

 

Subaru now recommends a Top Engine Maintenance procedure, had it done on a 2021 Forester with GDI 2.5L at Kenny Ross Subaru in Irwin, PA when I bought the pre-owned certified vehicle with 34,400 miles on it. Subaru recommends this treatment at 30kmi. intervals, 3 stage: fuel line/injector cleaner in fuel tank, removing throttle body and cleaning butterfly and walls with their solvent, and the questioned intake manifold vacuum feed of some pretty potent Subaru top engine solvent. Do not feed this solvent too fast into engine or you may end up with vapor lock. That is why I had them do it, all GDI engines suffer from carbon build-up on the intake valves, and Preventive Maintenance is just that: 100 MILES FROM HOME YOU GO INTO LIMP MODE AND TAKES YOU TWO DAYS TO GET BACK!! Anyway, I try to listen to the guys that built the engine. Breaking down on American highways today may cost you more than a tow charge!

 

RECOMMENDS is not the same as REQUIRED. This fuel system treatment is NOT listed at all (at least in the 2024 owners manual), but has been discussed in other threads:

See post#25 for vid, and post#43 for my lengthy response.

https://www.subaruxvforum.com/threads/decarbonization.189264/?nested_view=1&sortby=oldest#replies

 

SOA should have released a TSB for "Top Engine Maintenance Procedure".
Please provide the TSB number if it is available.
If there is some other SOA official document, can you say what it is so I can get a copy from my Subaru Service Advisor.
Since I have the Subaru Extended Service Agreement I am only go to do maintenance that is officially required by Subaru, and what is listed in the WARRANTY AND SERVICE manual.
I have a 2024 Crosstrek with 2.5L engine, so this may or may not apply to my vehicle.

 

https://www.subaruxvforum.com/threads/tsb-09-74-21r-cleaning-procedure-for-carbon-deposit-removal.180971/

 

Thanks for the TSB. I'll check with my Subaru dealer and find out if it is applicable to my model year.

 

96K on my 2014 and I have been told more than once, let the sleeping dog lie. Change your oil and filters and pay attention to any new or different sounds or feel in driving.

 

As I looked further into the TSB, yes it's for GDI engines up to 2021. Looks like starting in 2022 Subaru increased the size of the PCV system Hoses and PCV valve are different PN's and larger diameter. I'm not stating that newer vehicles are not susceptible to intake valve buildup, but looks like they have taken at least SOME steps toward alleviating it as the TSB has not been updated to include any of these with the newer larger PCV system.

 

The U.S. is Subaru's largest market, so I doubt they would risk it over some 'carbon buildup.' I'm sure they've made modifications to alleviate the situation.

 

Wishful thinking.