Does anyone know, or have a suggestion, where the top engine cleaner should get sucked in on the XT? The dealership suggested the kit at my current mileage. Throttle body has been cleaned and injector cleaner ran through a tan of gas. I just can't find a reasonable port for the top engine cleaner.
Peep6543
The TSB in this post might help
www.subaruoutback.org
Direct Injection, Carbon Buildup, and Oil Dilution
I would appreciate everyone's opinions and insights..... Should we expect that Subaru direct-injection engines will not suffer from the same carbon build-up issues other manufacturers have experienced? From everything I've read (and what is in the 2019 Forester), I expect the 2020 Outback 2.5...
www.subaruoutback.org
Updated TSB I never attached to the thread…. This one has pictures of the 2.4 purge valve location….
here ya go
![Image]()
here ya go
Benny can you verify that this is not available at @subaruonlineparts ?
parts.subaruonlineparts.com
Pea Carbon Cleaner Tool SOA868V9432 | SubaruOnlineParts.com
SOA868V9432 - Pea Carbon Cleaner Tool
parts.subaruonlineparts.com
That link is old hat… new hotness.
2023 Subaru Outback 2.4R-T Pea cleaner tool (carbon) - SOA868V9432 - Genuine Subaru Part
Pea cleaner tool (carbon). 2023 Subaru Outback 2.4R-T. Genuine Subaru Part - SOA868V9432
parts.subaru.com
Done. I had a low to medium amount of smoke so I take that as a good sign. I am the furthest from an engineer but as I understand it, the DI engines actually don't get as much carbon build up on the valves so there shouldn't be loads of smoke?
RPMs bogged a little during but after completing it seems to be running smoothly.
RPMs bogged a little during but after completing it seems to be running smoothly.
If you do an induction cleaning, you should change your oil afterwards to get rid of the extra solvents that get into the oil.
The Hyundai, Audi, BMW/Mini GDI engines were especially bad with the intake valve carbon so as mentioned, Subaru knew of this issue and mitigated it in their GDI designs, so it definitely won't be as bad as those cars, but over time it will still have some build-up, more than with a port injected engine.
Some GDI engines also have port injectors - Toyota D4S for example, but in a pure GDI engine like ours, fuel never touches the back of an intake valve.
The source of carbon on intake valves, which get very hot, is oil weeping down from valve guides, as well as oil mist from the PCV system. It's possible that the choice of oil affects how much carbon builds up on the intake valves. Newer SP/GF6 oils are designed for the challenges of GDI but I'm not aware of specific intake valve deposit tests/standards in those specifications. Some people seek out oils with low Noack, with the presumption that oil that vaporizes with heat will get sucked into the intake system and cause more deposits than oil that is more heat stable, but Gokhan from BITOG who is somewhat of a guru-type says in this thread: https://bobistheoilguy.com/forums/threads/noak-evaporation-and-gdi-engines.324400/
It's Noack -- the last name of the scientist who invented the procedure. I've been saying this over and over: It is not distilled evaporated-oil vapor that comes from the PCV and deposits on the intake valves -- it is liquid oil-mist droplets that contain the whole additive package with ash. Therefore, Noack does not directly affect the intake-valve deposits (IVD). However, the base-oil quality does affect the IVD, and the Noack is inversely proportional to the base-oil quality for a given base-oil viscosity. For example a PAO-and-AN-based oil like Mobil 1 Extended Performance 0W-20 (not the other viscosity grades) or a GTL-based oil like Pennzoil Platinum with PurePlus (all viscosity grades) will help. Nevertheless, you won't see a difference between PPPP 0W-20 and PPPP 10W-30 even though their Noack's vastly differ, as their base-oil quality is the same. The following all help: lower sulphated ash, higher base-oil quality, more antioxidant, and (possibly) less VII. Noack does not directly help.
Possible mitigations that auto-makers have implemented:
Mazda has a way of super heating intake valves so that the carbon is supposed to burn off.
Subaru has built-in air oil separating baffles to make the PCV vapors have less oil mist.
Some manufacturers may time injection cycles so that sometimes the intake valve is still open when the direct injection spray happens, and in that case, fuel mist will swirl and reach the back of the intake valve. Not sure what brands do this.
Subaru may have additional mitigations that I'm not aware of, but there are still deposits on the back of the intake valve over time.
The Hyundai, Audi, BMW/Mini GDI engines were especially bad with the intake valve carbon so as mentioned, Subaru knew of this issue and mitigated it in their GDI designs, so it definitely won't be as bad as those cars, but over time it will still have some build-up, more than with a port injected engine.
Some GDI engines also have port injectors - Toyota D4S for example, but in a pure GDI engine like ours, fuel never touches the back of an intake valve.
The source of carbon on intake valves, which get very hot, is oil weeping down from valve guides, as well as oil mist from the PCV system. It's possible that the choice of oil affects how much carbon builds up on the intake valves. Newer SP/GF6 oils are designed for the challenges of GDI but I'm not aware of specific intake valve deposit tests/standards in those specifications. Some people seek out oils with low Noack, with the presumption that oil that vaporizes with heat will get sucked into the intake system and cause more deposits than oil that is more heat stable, but Gokhan from BITOG who is somewhat of a guru-type says in this thread: https://bobistheoilguy.com/forums/threads/noak-evaporation-and-gdi-engines.324400/
It's Noack -- the last name of the scientist who invented the procedure. I've been saying this over and over: It is not distilled evaporated-oil vapor that comes from the PCV and deposits on the intake valves -- it is liquid oil-mist droplets that contain the whole additive package with ash. Therefore, Noack does not directly affect the intake-valve deposits (IVD). However, the base-oil quality does affect the IVD, and the Noack is inversely proportional to the base-oil quality for a given base-oil viscosity. For example a PAO-and-AN-based oil like Mobil 1 Extended Performance 0W-20 (not the other viscosity grades) or a GTL-based oil like Pennzoil Platinum with PurePlus (all viscosity grades) will help. Nevertheless, you won't see a difference between PPPP 0W-20 and PPPP 10W-30 even though their Noack's vastly differ, as their base-oil quality is the same. The following all help: lower sulphated ash, higher base-oil quality, more antioxidant, and (possibly) less VII. Noack does not directly help.
Possible mitigations that auto-makers have implemented:
Mazda has a way of super heating intake valves so that the carbon is supposed to burn off.
Subaru has built-in air oil separating baffles to make the PCV vapors have less oil mist.
Some manufacturers may time injection cycles so that sometimes the intake valve is still open when the direct injection spray happens, and in that case, fuel mist will swirl and reach the back of the intake valve. Not sure what brands do this.
Subaru may have additional mitigations that I'm not aware of, but there are still deposits on the back of the intake valve over time.
I know this an older thread, but what mileage should I be thinking about doing a Top Engine Clean? 2023 2.4 Touring XT.
If you go by Subaru's TSB, it should be done when you have symptoms, not at a certain mileage interval. If you did want to do it as part of routine maintenance, I wouldn't do it more often than once every 50,000 miles or so, and again, only immediately before an oil change.
The full Subaru procedure is pretty involved and there are simpler though probably less effective half measures, like using STP Pro Series Intake Valve Cleaner for a one-person job, or CRC intake valve cleaner for a 2 person job. The Ascent thread is helpful:
The ultimate intake valve cleaning would be to use walnut blasting - Direct Injected WRX guys do this as needed.
The full Subaru procedure is pretty involved and there are simpler though probably less effective half measures, like using STP Pro Series Intake Valve Cleaner for a one-person job, or CRC intake valve cleaner for a 2 person job. The Ascent thread is helpful:
The ultimate intake valve cleaning would be to use walnut blasting - Direct Injected WRX guys do this as needed.
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