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2015 Forester Limited
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Discussion Starter #1
Hi, the dealer said I had "carbon buildup on my engine" and recommended removal using the "Engine maintenance kit". It apparently comprises:

Fuel Injector Cleaner (SOA868V9150), a gas tank additive that cleans fuel injectors and intake valves without disassembly
Throttle Plate and Induction Cleaner (SOA868V9170), a high-pressure aerosol chemical mist that cleans throttle plate and idle air controller components, and
Top Engine Cleaner (SOA868V9160), a mist that removes soft carbon deposits from the intake plenum and valves, upper cylinders, and compression rings. Application requires Top Engine Cleaner Tool (SOA868V9430).
• Cleans fuel/air induction systems
• Removes soft carbon deposits
• Improves idle and fuel mileage
• Restores lost power and acceleration
• Reduces emissions
• Safe for oxygen-sensors/catalytic converters

I thought I read that you can't clean [intake valves?] from the inside because they never come into contact with the inside, and you need to do a walnut something or manually remove and scrape [only parroting random bits I remember reading, I have no idea what I'm talking about]. What additional questions should I ask the guy to better understand what needs to be cleaned and what I should do?

Thanks so much,
GES
 

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2001 Forester
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1,640 Posts
Walnut shell blasting process is the only sure fire way of cleaning the back side of the intake valves. But as @Even_Stephen asked, is your engine running fine? No mis-fire, pulls fine from stop? Then do nothing. The best way to prevent carbon build-up on the back side of GDI engine valves is to use high quality synthetic engine oil that prevents the oily mist from getting sucked back into the engine and sticking to the back side of the valves.
 

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2015 Forester Limited
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Discussion Starter #4
Walnut shell blasting process is the only sure fire way of cleaning the back side of the intake valves. But as @Even_Stephen asked, is your engine running fine? No mis-fire, pulls fine from stop? Then do nothing. The best way to prevent carbon build-up on the back side of GDI engine valves is to use high quality synthetic engine oil that prevents the oily mist from getting sucked back into the engine and sticking to the back side of the valves.
Thanks. I think the engine is good? What would a "Not pull fine from a stop" feel like? Every so often it feels like there's a tiny shudder. Is it true that every so often I should put in premium gas to clean out the inside of the engine?

Thanks for your advice!
GES
 

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2001 Forester
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"Not pull fine from a stop", means you notice a slight drop in performance compared to when you first drove off the lot. The carbon build-up on GDI engines results in the intake valves not seating completely when they close and therefore during the compression stroke there is a slight leak resulting in a drop in power. Putting in premium gasoline will not help because the gasoline never hits the backside of the intake valve and therefore the cleaning properties of gasoline will never clean the backside of the intake valve.

How many miles/km do you have on this engine. The shudder could be a symptom of carbon build-up. Could be anything in the drive train.

I'd suggest finding a non-dealer Subaru specialist for a 2nd opinion regarding the shudder and possible carbon build-up.
 

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2015 Forester Limited
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Discussion Starter #6
"Not pull fine from a stop", means you notice a slight drop in performance compared to when you first drove off the lot. The carbon build-up on GDI engines results in the intake valves not seating completely when they close and therefore during the compression stroke there is a slight leak resulting in a drop in power. Putting in premium gasoline will not help because the gasoline never hits the backside of the intake valve and therefore the cleaning properties of gasoline will never clean the backside of the intake valve.

How many miles/km do you have on this engine. The shudder could be a symptom of carbon build-up. Could be anything in the drive train.

I'd suggest finding a non-dealer Subaru specialist for a 2nd opinion regarding the shudder and possible carbon build-up.
Thanks for the kind explanation. Is the backside of the intake valve the only place where carbon would build up?
I bought my 2015 Limited 2.5 used in April, at that time it had 133K miles on it. Now it has 136K miles.
I live in a relatively small community (Wilmington NC) - I searched for a non-dealer Subaru specialist but wasn't successful. Is it worth it to drive out of town to find a Subaru specialist? JAX is 70 miles, Fayetteville is 90 miles, Raleigh is 130 miles. The dealership I went to was in Myrtle Beach, 80 miles, because my local dealership wouldn't even return my call to schedule an appointment.
GES
 

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2001 Forester
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The carbon build-up is mainly on the back-side of the intake valves. Prior to GDI engines, port injectors would spray fuel/gasoline onto the back-side and clean the intake valves, but with GDI the fuel is inject directly into the combustion chamber and bypasses the valves. The combination of EGR (carbon) valves and PCV systems carry oily mist from crankcase to be re-burned by the engine, results in carbon and oily mist building up and sticking to the back-side of the intake valves.

Yah, that's high enough mileage to potentially have carbon deposits. What you want is to find someone with a camera/scope to look at the intake valves without taking too much apart.

Does not have to be a Subaru specialist, but a independent shop that does work on Subaru will work. Here in Dallas there are not really any Subaru only shops. However there are several Japanese/foreign vehicle performance shops that work on Nissans, Acura, Honda, Subaru, etc....that do excellent work on Subaru. So if you can find a similar "performance" shop in your area that may help.
 

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Can of sea foam in the tank a couple times in a row
Sea foam does nothing for cleaning intake valves. It never makes it to the back side of the intake valves. Walnut shell blasting is the only way to clean intake valves. The DIY method is to take the intake manifold off, and use various brushes, cleaning implements to hand clean the intake valves. There are various youtube videos of owners doing this with reasonable success.
 

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2015 Forester Limited
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Discussion Starter #11
The carbon build-up is mainly on the back-side of the intake valves. Prior to GDI engines, port injectors would spray fuel/gasoline onto the back-side and clean the intake valves, but with GDI the fuel is inject directly into the combustion chamber and bypasses the valves. The combination of EGR (carbon) valves and PCV systems carry oily mist from crankcase to be re-burned by the engine, results in carbon and oily mist building up and sticking to the back-side of the intake valves.

Yah, that's high enough mileage to potentially have carbon deposits. What you want is to find someone with a camera/scope to look at the intake valves without taking too much apart.

Does not have to be a Subaru specialist, but a independent shop that does work on Subaru will work. Here in Dallas there are not really any Subaru only shops. However there are several Japanese/foreign vehicle performance shops that work on Nissans, Acura, Honda, Subaru, etc....that do excellent work on Subaru. So if you can find a similar "performance" shop in your area that may help.
OK, thank you very much for the detailed feedback, really appreciate it. So conclusions: #1 dealership was FOS. #2 Find a broader shop that focuses on Japanese imports. Got it. Will report back with results! (may be a few weeks, a little strapped for cash, but if you think it's time critical then I will get on it)
GES
 

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2019 Forester Limited
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What you want is to find someone with a camera/scope to look at the intake valves without taking too much apart.
Scopes don’t cost what they used to. Does anyone know how much work is involved in getting the engine to a point where one can view the valve backside? I looked for this info awhile back and came up empty. Would consider getting my own, if the work to inspect isn’t crazy.
 

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2019 Crosstrek 2018 XT
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Sea foam does nothing for cleaning intake valves. It never makes it to the back side of the intake valves. Walnut shell blasting is the only way to clean intake valves. The DIY method is to take the intake manifold off, and use various brushes, cleaning implements to hand clean the intake valves. There are various youtube videos of owners doing this with reasonable success.
Obviously I understand that. My point is that the dealer has no clue what is causing the problem. It could certainly be that the injectors coule benefit from the Seafoam or equivalent injector cleaner. No one here can say there is buildup on the intake valves that is "causing"his problem.
 

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Sahuarita, Arizona USA 2018 Forester Limited
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@ges74 If your 2015 is a non-turbo you do not have GDI/direct injection engine. Fuel will clean the intake valves on port injection engines especially if you use a Top Tier brand of gasoline such as Chevron, Shell, Costco, QT. So if you don't have a turbo the best thing you can do to prevent carbon buildup is to fuel up with a Top Tier brand.
 

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2015 Forester XT Touring CVT
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@ges74
@ForesterBill Is right, no carbon deposit issues with your engine. Dealer is just being dealer... I would watch for oil consumption with your engine. Small percentage had that issue (even less with CVT) but I would keep an eye on it
 

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‘14 FXTT; '15 Legacy FB25
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As has been mentioned, the OP's engine is the FB25, which is NOT direct-injection. If the OP is at all concerned, then using top-tier gas will likely be enough to keep the engine clean, since each injection of fuel passes by and cleans the intake valves.

It doesn't hurt use cleaners, however:

Seafoam is OK; however, alternately using a heavy solvent, like Berryman B12 chemtool and later something with a high concentration of Poly Ether Amine (PEA) will work wonders IF there is any buildup. High-PEA cleaners include Gumout w/ regane (they actually label their products that contain PEA now), Redline SI-1, Chevron Techron and several others that I don't use.

/

Finally, I'd swear I read somewhere that a lot of later GDI engines, the FA20DIT included, use AVCS to allow the intake valve to remain open for a split second after fuel injection to let some cleaning to occur. Regardless, the pictures I've seen online of modern GDI engines don't seem even close to as bad as those of yore.
 
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2018 Forester Manual
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Finally, I'd swear I read somewhere that a lot of later GDI engines, the FA20DIT included, use AVCS to allow the intake valve to remain open for a split second after fuel injection to let some cleaning to occur. Regardless, the pictures I've seen online of modern GDI engines don't seem even close to as bad as those of yore.
MOST of the current generation of GDI engines play with valve timing to let air / fuel 'puff' over the intake valve to keep it clean. The carbon buildup was a mid/late 00's early GDI type of deal. I bought a direct injection book for my father a few years ago -- he was interested in the technology. I read through it before gifting the book and it mentioned that many manufacturers employ that technique.
 

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2017 forester
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I've put a bottle of Chevron Techron in the next 2 tanks of gas after an oil change for the last 2 decades. Seems to keep out of trouble. I tend to use Tier 1 gas also but I dont go out of my way to get it. Make sure you get the more expensive Techron- Complete Fuel System Cleaner (cheaper one is just diluted version). Its exactly the same stuff the BMW dealer sells in a BMW marked bottle for fuel injector cleaner.
 
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