If they do a mechanical cleaning of the valves or a walnut blasting its not a rip-off (IMO)

 

Yes, carbon build up on the backside of intake valves with direct injection engines is normal. Yes this should be cleaned off periodically as a maintenance item. The service is not inexpensive. Subaru has a chemical process to clean the intake valves, but a walnut shell blasting is the better way in my opinion.

The reason why they are recommending the intake valve cleaning with the thermo-control valve replacement is because the intake manifold and one time use fuel pipe has to come off for both jobs. Subaru is paying for the new intake manifold gaskets, fuel pipe, and labor to remove and re-install the manifold so you're just paying for the intake valve cleaning service itself. Subaru is not going to pay for the intake valve cleaning until it starts causing a rough idle or misfire DTCs, which may be far later down the line when most warranties are expired.

 

Coupons are available on the MySubaru app or website.

Warranty aside, $575 for mechanical cleaning is a good price. I paid $900.

Below are photos of my 2015 before and after intake valve cleaning.

It had drivability issues - hesitations and felt like it was misfiring. Three applications of chemical cleaners didn't fix the issue. Mechanical intake valve cleaning fixed it and it runs so much better now.

It isn't a scam. It's the nature of these engines. Chemicals won't cut it. An air-oil seperator will help but even that will only slow the process.

Before...

After...

 

Carbon buildup is normal. Tune-up in a bottle is not the answer once the buildup occurs.

 

Agree. If you have direct injection nothing in the fuel is going to get to the top of the valves. You might end up with only shiny piston tops.

 

I would want to see before pictures. Intermittent start stop problems are usually related to 12V batteries in poor condition. If you haven’t replaced your 12V battery in the last two years, I would start there. Subaru uses a larger sized battery now, a Grpup 24F.

I have 130k miles on my engine, and it’s performing well. I would be surprised if you have carbon build up unless you’re using garbage fuel.

 

I would be surprised if you have carbon build up unless you’re using garbage fuel.

The 2019 Forester 2.5 liter engine is direct injected - fuel is injected directly into the combustion chamber and doesn't touch any part of the intake, including back of the intake valves.

In such an engine, carbon buildup on the back of the intake valves has nothing to do with fuel.

 

@TTiimm yes, poor oil and a stuck PCV valve will also cause buildup. I would expect rough operation and hesitation, but not intermittent start/stop functions. I’d expect for $500, the dealer is going to perform Subaru’s Top Engine Cleaner induction service, which is a literal $10 can they spray into the induction hose.

 

@Cddelta

Buildup is endemic to direct injected engines.

Poor oil, stuck PCV valve and a whole host of other issue can certainly exacerbate it. None of these apply to my car but it had lots of buildup. See the before photo in post #4.

That photo was taken subsequent to three applications of Subaru's top engine cleaner performed over a 5000 mile period. It didn't even put a dent in it.

If you have a direct injected engine then you have valve deposits. The only question is whether it is bad enough to cause driveablity issues. If it gets that bad then mechanical cleaning is required. Again, reference the before and after photos in post #4. This isn't something I made up.

$250 is what I paid for each application of the Top cleaner. $550 is about in line for a walnut blast. Most independent shops charge $600-ish.

The OP isn't being ripped off.

The PDF linked below is Subaru's process.

 

<snip>
The PDF linked below is Subaru's process.

It depends on the dealer.

At the dealership where my son works, they do not use the top engine cleaner or walnut blasting. They found with any sort of buildup the top engine cleaner is pretty worthless.

They have a special tool that essentially scrubs the back of the valves. As I recall the price is around $750, but price is going to depend on the dealer's labor rate.

 

@auntiesuebee

I'd be surprised to find out that the tool isn't an Autotool HTS558 walnut blasting machine. If it isn't then I'd like to know what it is. Maybe you could ask your son if you remember?

I'd love it if my dealer offered this type of service. The only shop I trust to do this is a very expensive local performance shop. $750 at the dealership would be welcome.

 

My alternate tool is zipties that go in my drill chuck. 😂 Helps break up the big sticky chunks into something easier for the walnut shells to devour.

 

There is actually a feature built into the 2019+ GDI engine that is designed, at least in part, to help reduce the build-up of valve carbon, but unfortunately @kiannasmiles7 decided to turn it off. That's a shame.

It's well documented that one of the downsides of GDI is carbon buildup in the intake above the valve seat. These engines run well at speed, but idling has been identified as the enemy. Poor breathing dynamics at low flow causes backswirl and the deposition of fuel up onto the lower intake, valve top and stem. AS/S reduces needless idle time, reducing the incidence of carbon build-up.

Yes, AS/S does save a tiny amount of fuel. But it's minuscule. On average I log about 12 ounces per tankful, or around 3 miles extra per fillup. Hardly enough to move the meter on the EPA test. But it makes a huge difference in terms of minutes of idle time per tankful. I often see as much as 20 minutes of idle elimination per tankful, prime-time carbon buildup damage not taking place. To me, that's a great reason to have and to use AS/S....

 

@j3rf

Do they need to be Subaru OE zip ties or can aftermarket zip ties be used?

Do the JDM STI zip ties perform better? Any compatibility issues?

 

@TTiimm As long as they are metric zip ties, it's good enough. I wouldn't use SAE or Imperial dimensional whips on a JIS engine. And certainly NEVER whitworth. I only give those house space because I gravitate to old British stuff. Generally incompatible.

 

I wonder what the OP would say if he knew that he might pay $550 to have his valves cleaned with zip ties.

 

I think some are somewhat missing the point. The quote is cheaper because they are already in there, with the intake already being removed. I don’t think any symptoms are occurring from the dirty valves. I may have missed it, but I don’t see the current mileage. The quote is a very good bargain IF it is a walnut blasting or equivalent (I don’t know what the equivalent would be.), and high praise to the dealership for offering this to you while your intake is off! I would look at the picture of the valves while noting the current mileage, and I would almost certainly get this done.

 

Volkswagen and a few other vehicle manufacturers had this very same problem. They ended up incorporating auxiliary injector(s) in the intake manifold to stem the carbon build-up issue with their engines in later generations. Those added injector(s) are only active part of the time and the ECU automatically keeps the A/F ratio at the proper levels.
Has Subaru incorporated this modified direct injection system into the later years vehicles?

 

Has Subaru incorporated this modified direct injection system into the later years vehicles?

The FA20D and FA24D from the BRZ have Toyota's D-4S dual injection system.

 

Unfortunately, you have a Direct Injection version of the engine, and carbon build up of the valves is normal and to be expected.
Older Port Injection-version of the engines have a fuel mist (with air, of course) passing over the valves, so a fuel additive like Techron (or Shell's V-Power premium fuel) will wash away the deposits.
But newer Direct injection engines only have air passing over the valves (the fuel bypasses this area and is injected directly into the combustion chamber, hence the name "Direct Injection"), so there's no way to use a fuel "cleaner" to decarbon the valves with a fuel additve.

 

The trade-offs of DI engines are well known: better performance / more maintenance. If it were my car, I would jump on the $575 offer. I have done the job on Mini-coopers by hand. It is tedious, time-consuming, and potentially dangerous if I do not get each cylinder at TDC before the clean. Adding to the fun, the chemicals required to make the job easier are not exactly health farm-approved. I went through a dozen brass brushes in my drill for 4 cylinders. While I love DIY, I will buy a walnut blaster before doing it myself again. We use walnut sheels to clean brass for shell reloading. A great abrasive. Best of luck.

 

It's worth commenting on chemistry as a first try before intake removal to address valve carbon. Subaru does have a cleaner, and it's use is covered in the manual and TSB's. Polyetheramine (PEA) is bled into the intake tract after the throttle body and above the valves. The flow rate is low, emptying a small bottle in about an hour to soak the carbon buildup and partially decompose it. How effective it is likely depends on how bad the build-up is.

I still prefer prevention. Idling is the enemy of DI engines, and promotes carbon buildup.

1) Start your car and don't let it idle to warm up. Even in winter I have it in gear and gently accelerating within about 10-15 seconds.

2) When you aren't driving (sitting & waiting...) shut off the engine. In most cases, a little cold won't kill you.

3) Let your AS/S system do it's job. Eliminating 20 minutes of traffic light idling per tankful goes a long way towards preventing carbon buildup.

 

Idling is the enemy of DI engines, and promotes carbon buildup.

Why is that?

 

I read an SAE analysis on this. Paraphrasing....

Port injection provides plenty of time for effective mixing of fuel and air above the valve. In fact, fuel is sprayed directly onto the stem and valve top / valve seat region. The fuel wash lowers valve temperature, reducing contact carbonation. Detergent gasoline spray breaks and prevents carbon buildup.

DI sprays the fuel into the cylinder. Great mixing and complete burn takes place at high idle thru redline. But because of the swirl pattern and reduced air packing at idle speed, mixing isn't as complete, so the burn tends to be dirty. And the low rpm exhaust manifold pull doesn't scavenge all the exhaust and unburned fuel effectively from the cylinder. On the next cycle, some of this unburned fuel / exhaust mix backwashes thru the open intake valve up into the intake manifold. You'd have to examine valve timing and overlap to throughly understand why flow doesn't follow the expected direction. Valve stem and top temperatures are considerably hotter on GDI engines as they lack the fuel spray evaporative cooling. That backwash flash carbonizes onto the valve top and stem.

That's the jist of it. Having the engine shut down (AS/S) at 600 RPM idle cuts that fuel backwash by 300 injector pulses per minute.