[lidksmy]

Am I making a big deal out of this,

Yes.

... is it possible to get direct injection and turbo right and make it reliable with no carbon build up?

Yes.

 

[Justin3.6R]

Run some BG product thru the system once in a while. Both Chevy and Subaru recommend it..

 

[gt1953]

W T H I BG now figuer that one out....I am asking what the heck is BG. Is it a big gun or bad gas not really sure a S M P= so many people never spell out stuff or even have a reference to it.

 

[Jon89]

It is a fuel system additive that has been around for a number of years. It may be called BG44K. Google it and see what you come up with. It and Chevron's Techron product are really the only fuel system cleaners that are worth spending money for.

 

[Flat6Brick]

Get an oil separator (catch can) and you'll be good to go. Not sure if they make one for the XT, but it makes things easy.

 

[RobertD]

Oil dilution and carbon build up will affect all direct injection engines from all car manufacturers the same. Most cars these day have direct fuel injection for improved emissions and have the same potential issues. But if you are like me you only see the issues on Subarus because I usually only look at the Subaru forums and turn a blind eye to others. So I forced myself to look at other car forums and just as I thought it is a common issue with common responses like when will Subaru/Toyota/Honda/GMC/etc wake up and realize they have a problem with fuel dilution. Guess what they all know it is a common problem with direct injected engines.

If you live in the colder climates and mainly drive short distances and don't let the oil heat up which lets the fuel that went past the rings (especially on cold start ups) evaporate then you may have fuel dilution issues. I live in the south and most of my trips are 30 miles or more so I do not have the fuel dilution problem. When I visited NJ and Penn this winter and got caught in a bad (to me) winter storm I thought I smelled fuel when I checked my oil once. It went away the next day driving 400 miles south.

Carbon build up on the newer direct injection engines is around the intake valve. When fuel was injected and went past the intake valve it would clean the intake valve. Now the fuel is injected directly in the cylinder the intake valve does not get cleaned with every fill-up. So the intake valve has the potential to get some carbon build up. I have an Ascent with the 2.4 turbo and have not been affected negatively by carbon build up in 92+K miles. My chevy truck also has direct injection and with 125+K miles has been fine. Usually if you do have carbon build up on the intake valve it can be cleaned with things like Sea Foam.

 

[lidksmy]

Oil dilution and carbon build up will affect all direct injection engines from all car manufacturers the same. Most cars these day have direct fuel injection for improved emissions and have the same potential issues. But if you are like me you only see the issues on Subarus because I usually only look at the Subaru forums and turn a blind eye to others. So I forced myself to look at other car forums and just as I thought it is a common issue with common responses like when will Subaru/Toyota/Honda/GMC/etc wake up and realize they have a problem with fuel dilution. Guess what they all know it is a common problem with direct injected engines.

If you live in the colder climates and mainly drive short distances and don't let the oil heat up which lets the fuel that went past the rings (especially on cold start ups) evaporate then you may have fuel dilution issues. I live in the south and most of my trips are 30 miles or more so I do not have the fuel dilution problem. When I visited NJ and Penn this winter and got caught in a bad (to me) winter storm I thought I smelled fuel when I checked my oil once. It went away the next day driving 400 miles south.

Carbon build up on the newer direct injection engines is around the intake valve. When fuel was injected and went past the intake valve it would clean the intake valve. Now the fuel is injected directly in the cylinder the intake valve does not get cleaned with every fill-up. So the intake valve has the potential to get some carbon build up. I have an Ascent with the 2.4 turbo and have not been affected negatively by carbon build up in 92+K miles. My chevy truck also has direct injection and with 125+K miles has been fine. Usually if you do have carbon build up on the intake valve it can be cleaned with things like Sea Foam.

To be clear, you are referring to fuel dilution of the oil.

 

[PilotXT]

Fuel system cleaners won’t clean the intake valves which is the problem with direct injection. It is not simply a turbo DI vs naturally aspirated DI type of issue. Direct injection is direct injection.

There are service you or your dealer can do if you need to. Thus far, no expectant DI issues with FA24 since Ascent introduction and rollout to Legacy and Outback and also for the FB25 in Foresters and Treks.

If it’s a 60k thing for preventative maintenance, so be it.

 

[ArF193]

The direct injection is not for the benefit of the engine or owner, it is for the benefit of the EPA demands.

We have two groups here, those that want and love the turbo and those that don't. I looked at the turbo as another failure point the same way I looked at the moonroof. The turbo will need to be rebuilt at some point, hopefully later than sooner. If I lived in Denver I would have purchased the turbo but would be purchasing something different than their local 85 octane regular gas.

 

[RobertD]

To be clear, you are referring to fuel dilution of the oil.

Yes

 

[jholmes8]

It is a fuel system additive that has been around for a number of years. It may be called BG44K. Google it and see what you come up with. It and Chevron's Techron product are really the only fuel system cleaners that are worth spending money for.

In my old job, we were trying to develop an aftermarket additive to clean intake valves on GDI engines. We tested all of the major ones on the market from BG to STP, etc. None of them cleaned intake valves on a GDI engines. Even the ones that mist into the intake with the engine running had no affect on intake valve deposit weight (we weighed the valves before and after by removing them). We did find some additives that made the valves worse but none that cleaned them in any significant way.

The other claim you will see for these additives is that they will remove port and/or direct injector deposits. What they don't tell you is that injector deposits really haven't been an issue since the 1990's. Other than a few poorly designed injectors out there (some of the very early direct injectors were prone to deposits), there really aren't any injector deposits seen in used cars and we tried to find them. We had an additive that would create direct injector deposits but we couldn't find any used cars that had harmful levels of injector deposits.

After working in the fuel additive industry for 13 years, my take away is that aftermarket additive aren't worth the money as they are mostly cheap solvent, unless you need to clean a carburetor (like I used to do in my 1976 Honda GL1000). In a few cases, we saw valve deposits and such actually get worse with some aftermarket additives. You are better off spending a few extra cents per gallon for Top Tier fuel if you really want to be careful. If you are really worried about deposits, then get a tank of premium fuel from Shell or BP or Exxon as they use a much higher level of additive in their premium fuel.

I buy the cheapest gas I can find as even EPA LAC (lowest allowable concentration) works fine. More additive isn't always better...

 

[CASkiBum]

I have been lurking around this and other forums discussing GDI and carbon fouling. Here is an article which I found to be a good summary of the current knowledge: GDI System Maintenance: Preventing Misfires & Carbon Buildup On Intake Valves – UnderhoodService

I'm planning my purchase of a '24 OB Wilderness for later this year, and I am concerned about carbon fouling of the intake valves. I have researched oil catch cans, AO separators, aerosol chemical measures to 'remove' carbon, walnut blasting, etc. Here is the point that I reached a certain comfort that will allow me to buy my $40k car:

(1) All GDI engines suffer Carbon Buildup.
(2) Most chemical solutions MAY slow deposit accumulation, but will not prevent it.
(3) Using top tier synthetic oils with 4k-5k change interval, and top tier fuels, will also mitigate, but will not prevent.
(4) Driving habits will mitigate but not prevent.
(5) Sometime around 80k-100k I will likely perform a walnut blast of the intake valves.
(6) Likely that by 200k miles, when walnut blasting would be required again, the car will have other issues, so this will be a decision point.
(7) Yeah, walnut blasting sucks, but it is no worse than replacing a timing belt, which we no longer have to do.
(8) Most of the 'junk' caught in aftermarket catch cans is stuff that would be burned in the combustion chamber anyway. AOS in particular would be included as standard if they really worked.

Other than carbon issues common to all GDI engines, the FA24DIT looks like a pretty solid motor.

Comments welcome.

 

[Shortround]

I've been through a process of plusses and minuses similar to CASkiBum -- the clincher for me to settle on just having a walnut blasting done once its needed is I went to a subaru enthusiast mechanic clinic recently where I could ask all sorts of questions. The carbon build up treatments may work to some extent, but they won't hold a candle to having the carbon physically removed via blasting. There's a risk that using a spray-in cleaner would cause problems further down the line like blowing carbon bits into the combustion chamber and into the catalytic converter, as well as other downstream sensors like the O2 sensor in the exhaust.

Another point to think about is - when have you ever had something realllllly dirty, and you decided to only spray some solvent on it to clean it up? I know its not a perfect method, but just from a logic standpoint, it seems like a flawed method. Will it help remove some carbon? Sure! But it's not a cure and a blasting will eventually be needed, so just save your money for some walnut blasting.

The advice from the mechanics was to perform oil changes early and often (depending on your driving), and to run top tier gas to prevent buildup. Aside from that, buildup will happen one way or another, you just have to be prepared to handle it as a maintenance item.

 

[dovidan]

Regarding fuel dilution of the oil, according to recent report by Blackstone Labs fuel dilution is not very common on GDI engines unless they are hybrids. Even then, fuel dilution is not a huge worry as long is oil dipstick level isn’t rising. See this 2025 report: Is Fuel Dilution Just a Hybrid Thing? | Blackstone Laboratories

 

[SilverOnyx]

I just read the report you linked to and my take-away is different than yours.

• Short trip driving in a non-hybrid will increase fuel dilution.
• Fuel dilution is bad, causing deposits in addition to weakening the oil.
• Frequent oil changes mitigate this if you have significant fuel dilution.
• Another mitigation would be to drive 15 minutes on the highway to burn off excess volatile contaminants like fuel and moisture.

So, there does not seem to be a correlation between hybrids, fuel, and excess wear, much less premature engine failures. Regardless, it’s obviously better to have less (if any) fuel in your
engine oil; the less contamination, the more the oil is going to function as designed and tested by the manufacturer. So how can we accurately judge the risk, and mitigate fuel dilution, if noted?
Above all, it’s important to monitor the oil level at the dipstick – if fuel dilution is noticeably displacing the oil level, it’s worth inspecting the fuel system, no matter the reason. It’s also worth
making note if your engine is starting to consume oil, since it can be a sign that the oil control rings are no longer working correctly, which could lead to problems with your catalytic
converter as well as pre-ignition and detonation issues. Hybrid vehicle or not, any combustion engine can develop acute fuel system issues that are worth addressing promptly.

But as for the smaller, nuisance amounts of fuel dilution? It never hurts to work the engine a bit harder every now and again, to generate the heat it takes for fuel to evaporate—for example,
hopping on the highway for 15 minutes or so, if that’s not a normal part of your routine. More frequent oil changes can also help to flush out any fuel that’s mixing with the oil, before it can
accumulate to problematic levels.

 

[Silver_Sport]

I've recently read over on Bob Is The Oil Guy (BITOG) that Blackstone does not do a proper test for fuel dilution in motor oil (chromatograph) and that their test is flawed...I am not sure if this is true but those who know more than me on these tests think you might want to use other testing facilities for getting a true look at fuel dilution in your oil...

Good luck with your choice

Bill

 

[Wonderlost]

I am not planning to walnut blast intake valves, but I may attempt to borescope the intake manifold at my first scheduled intake valve cleaning. I have non-intrusive intake valve cleaning in my maintenance program at 36,000 mile intervals. Here are the materials and procedure.

 

[bluesubie2]

I've recently read over on Bob Is The Oil Guy (BITOG) that Blackstone does not do a proper test for fuel dilution in motor oil (chromatograph) and that their test is flawed...I am not sure if this is true but those who know more than me on these tests think you might want to use other testing facilities for getting a true look at fuel dilution in your oil...

Good luck with your choice

Bill

It’s true. Blackstone provides an estimate which is extrapolated from the flashpoint reading. It is an ASTM method, although it is the least accurate and will always be lower than a true fuel reading by gas chromatography.

https://bobistheoilguy.com/forums/threads/blackstone-and-fuel-dilution.357356/

And a 15 minute drive does not always ”burn off” fuel in a Subaru DI. There are a lot of uoa’s of Subaru’s on BITOG where owner’s did a lot of highway driving yet still had high fuel. Higher oil temps are more effective.

 

[SilverOnyx]

Absolutely I did not think that an occasional 15 minute drive will effectively purge contaminants.

 

[dovidan]

I've recently read over on Bob Is The Oil Guy (BITOG) that Blackstone does not do a proper test for fuel dilution in motor oil (chromatograph) and that their test is flawed...I am not sure if this is true but those who know more than me on these tests think you might want to use other testing facilities for getting a true look at fuel dilution in your oil...

Good luck with your choice

Bill

That's my understanding as well. My OI was done by Amsol / Oil Analyzer Lab which supposedly has a more accurate test (don't recall the name of it).