2.4dit

Ok, so this engine has been in the field for a few years now and I'm wondering if the valve deposit problem inherent in direct injection engines has reared it's ugly head. I've seen no mention of it here for the Legacy but has anyone heard of it in Outback or Ascent?

I do not have a 7th gen, but my previous truck had DI, from my understanding this is eventually going to happen. In order to prevent it, I installed a catch can (requires periodic emptying) and used CRC GDI IVD Intake Valve and Turbo Cleaner once per year.

 

Had no problems for 5 years and 100k km until I sold the truck earlier this year.

The below is from a post on the Ascent forum (I'm a member because our other car is a 2020 Ascent) where a guy asked SOA about carbon build up on the FA24DIT. Here is SOA's response:

 

"Thank you for contacting Subaru. I appreciate the opportunity to be of assistance.

 

Older direct injection systems that experienced carbon build up were so called “lean burn” systems. Unfortunately these systems suffered many times from uneven combustion due to variations in the fuel and air mixture throughout the combustion chamber. This created a mix of lean and rich conditions resulting in variations in combustion temperature and uneven burning of the gasoline. This uneven burning lead to the condensing of unburned and partially burned hydrocarbons which over time resulted in carbon buildup.

 

Subaru engineers understood this when they created our current direct injection system. They developed innovative yet simple systems to manage and control the combustion variations inside the combustion chamber. These include features such as specially shaped piston crowns, multi-patterned injection spray, and tumble generator valves. All of which promote the precise swirling and intermix of fuel and air under the variable conditions required across the full range of power requirements. When combined with very high fuel pressures and extremely short injection duration of the Subaru direct injection system, stoichiometric combustion is maintained across the combustion chamber resulting in very even and complete burning. As a result abnormal residue and carbon deposits are not created and engine performance and fuel economy are maximized.

 

Please note that our research does show that routine maintenance, per the warranty & maintenance booklet, is another important factor when avoiding any potential carbon buildup concerns."

That's the kind of answer I would have liked from a SOC insider regarding the lack of Speed Volume Control and other sound adjustments on my Harman Kardon stereo. Maybe I should reach out to SOA... BTW, could you post the exact address at SOA? Edited July 28, 2021 by Mitaine

Maybe I should reach out to SOA... BTW, could you post the exact address at SOA?

 

The post just says he emailed SOA; it doesn't say what address he used to contact them. If I were to want to email them, I'd use the following URL: https://www.subaru.com/customer-support.html

Edited July 28, 2021 by LBSypher

SOA said that, but get a catch can or IAG or radium unit and feel safe.

ALL Direct Injection motors from ALL manufactures suffer from carbon buildup on the valves. The exception being some motors that are direct and port injected.

 

AOS helps a ton to keep the buildup down, but still plan on a walnut blast at 60k miles.

I see significant buildup as early as 30k miles on some cars.

ALL Direct Injection motors from ALL manufactures suffer from carbon buildup on the valves. The exception being some motors that are direct and port injected.

 

AOS helps a ton to keep the buildup down, but still plan on a walnut blast at 60k miles.

I see significant buildup as early as 30k miles on some cars.

 

Just to confirm, you're saying that you've seen firsthand or heard from owners of the 2.4 DIT that carbon build-up does eventually become an issue?

SOA said that, but get a catch can or IAG or radium unit and feel safe.

 

I know what a catch can is but not the other two nor how they are implemented.

For that matter I cannot fathom how PCV emissions are handled on a positive pressure intake system like a turbo.

 

So we have not heard from someone who has or knows of a Subaru 2.4DIT that's had valve deposit problems yet?

I like Subaru's answer to the question but in my mind it really doesn't address crank case emission deposits. Maybe I'm reading it wrong.

It's not a Subaru issue, it's a direct injection issue.

I perform the cleaning service on all makes and models and they are all equally dirty.

 

ALL direct injection engines have the same issue. They all need physical cleaning to remove the deposits.

 

You're not gonna get any information from SOA other than to follow the recommended service procedures.... which don't cover physical cleaning of the valves.

 

The factory PCV system directs all the emissions back into the engine to be burned. This causes carbon buildup on the backs of the valves. A Catch Can or Air Oil Separator tries to remove or catch these emissions before they are re-introduced into the engine and prevent the carbon buildup.

 

The 2.4 DIT suffers from the same carbon buildup that the 2.0DIT and all other Direct Injection engines have.

so basically, if you buy a new one, put in a catch can after you take delivery.

so basically, if you buy a new one, put in a catch can after you take delivery.

 

And hope your dealership doesn't blame the aftermarket piece you put on the engine if you have any issues down the road while under warranty.

Is there a particular brand or style of catch can folks here recommend? Are there directions available to install it?

I'm still not sure how PCV works on a forced induction engine as I'm used to engines with vacuum in the intake, not a positive pressure. Would a catch can work on the turbo engine?

And hope your dealership doesn't blame the aftermarket piece you put on the engine if you have any issues down the road while under warranty.

 

Have you installed a catch can? How do you intend to mitigate the valve deposit problem?

 

How much is this walnut blasting service that should be done every so often? I drive 25K a year and would hate to have to spend $700 a year to deal with an issue a catch can would handle for a couple hundred bucks permanently.

I have not seen a catch can or AOS kit for this engine, but fair warning, a catch can must be emptied. If not there could be issues, probably not good ones, emptying can be quite frequent in the winter, in my experience.

Have you installed a catch can? How do you intend to mitigate the valve deposit problem?

 

How much is this walnut blasting service that should be done every so often? I drive 25K a year and would hate to have to spend $700 a year to deal with an issue a catch can would handle for a couple hundred bucks permanently.

 

I had a Crawford Performance AOS on my '08 STI. However, I do not have one on my 2020 Ascent nor on my 2021 Legacy XT (Crawford doesn't make one yet). Both cars have the 2.4DIT engine and both have Subaru extended warranties. I'm not yet convinced carbon build up will be an issue based on the mitigation Subaru has built into the design of this engine, but IF carbon deposits become an issue while the cars are under warranty, I will have them walnut blasted. If I still own these cars when they are no longer under warranty, I will add an AOS if carbon build up is an issue and potentially buy the equipment I need to do the walnut blasting myself. I already have the air compressor so it shouldn't be too expensive.

I think that, for most people, the best insurance against potential issues in the future is the CRC Intake Valve Cleaner. Even if you were to install a catch can, it needs to be regularly emptied, which is hard to start on top of. An AOS is alot of work to install and $$$, especially given that there is no off-the-shelf kit.

 

I have used the intake valve cleaner a few times with my previous vehicle, it takes two people, but is not horribly involved.

I still haven't seen anyone post anything on Ascent, Outback, or Legacy forums stating absolutely that carbon build up is an issue on the FA24 DIT engine. I know it is an issue on other (older) DIT engines including the FA20 DIT as I had one and have seen it.

 

My two FA24 DIT engines are too new (i.e. low mileage) to see the issue yet, but I know that there are lots of folks on the different forums who have tons of miles on their engines. However, I have searched and haven't been able to find anyone having the carbon buildup issue.

 

Is it possible that Subaru was right and their design changes to mitigate the issue are working? I mean, other manufacturers of DIT engines have found ways to mitigate the issue. Has anyone found someone with actual pictures of the issue on the FA24 DIT?

 

When my warranties run out, I've got no problem with buying and installing an AOS for each of my cars once someone builds it (I've done it before and it is pretty straightforward). I just want to make sure I'm not spending the money unnecessarily.

Awesome, helpful info, thanks for posting!