I do not like the side effects of DI aka carbon buildup and there's nothing in a pure DI system that mitigates it, at least from an engine standpoint.


We can use oils designed to mitigate (not eliminate) the concern or perhaps we can hope that Subie uses a double injection system like Toyota. Since Subie and Toyota have interests in each other, perhaps some of the technology flows back to Subie.


That said, I don't think most ordinary Joes, Janes, binary or non-binary life forms care all that much. Car enthusiasts do since we bite our nails over things like this. If people drive 12k a year and the onset of carbon buildup is gradual, will someone have a moment of glorious realization that there's carbon in the engine? Doubtful. Most people will likely not notice a thing, especially if they do a lot of freeway driving. Around town people might even be less in-tune with their cars.


In the end, the carbon issue is still unresolved and engineers will figure it out but I'm not putting on my best knickers for a new car until they do. DI has a lot of upside but a horrible maintenance downside. There's nothing you can put in the gas tank to wash the valves and the only thing is an air intake treatment but that's a very limited type of cleaning.

 

Exactly?! I’ve been saying this (well “thinking” it) for several years? Biting my nails and telling people that there is definitely a “used car Armageddon” from 2016-2024 most likely? (And no one cares... while I bite my nails.) Even the Corolla motor is the “solution” but is now more complicated and I’m KINDA wanting to see one “generation” of issues/kinks worked out before jumping in? So if Subaru is not adopting right now, they are either letting TOYOTA be the guinea pig and will have a better one in 2022+ in the Impreza etc or they will be 4-5 years behind. So when can I finally show my Subie love again? (My best knickers are already gathering lint!?)

 

doesn't the BRZ use a hybrid system? maybe that will move to the newer gen, engines?

 

I owned a GTI before getting my outback and had to decarbon the intake 3 times during my 140k usage of it. I think the only solution that will exist is two fuel injectors. Costly solution though so I doubt we'll see it?

 

My 2017 Subaru Impreza has DI.... it starts nearly instantly at any temperature. The throttle is a bit 'touchy' whilst the engine is cold.

As for build-up on the intake valves..... time will tell. I know Subaru has a PATENTED centrifugal oil-separator builtin to the end of one of the camshafts in an attempt to mitigate the issue.

In the end.... it is the federal laws which are forcing automakers to use technologies such as Direct-Injecttion with the inherent problem of carbonizing the backside of the intake-valves. NO automaker is immune to the laws of physics so the Subaru DI system has the same possibility of this issue.

Look on the bright side.... the Timing Chain (instead of belt) does not have a replacement requirement....so now the intake-valves may need a regular cleaning. Think of it as a trade... one expenditure for another.

 

I know that VW has a procedure where they remove the intake manifold and use a hybrid sand blaster with walnut shells to blast the carbon off. They use a vacuum cleaner to vacuum out the walnut shells as they blast so as to not fill the cylinder. They also do their best to make sure the valves are closed also.
Still it is costly, but the head is not required to be removed.

 

If they follow Toyota's lead and some other asian's and Ford, they should have extra set fuel injectors spraying right into the valves, that should keep carbon at a minimum, plus some other advantages.
On the boxer engine, as long as the turbo doesn't get all tied up with the intake, its not bad job to do (cleaning intake ports).

 

It's still an unaddressed problem for Subaru. Combined with extra blow-by from the turbo, plus an EGR system, it's bad news for "just change the oil and drive"-type of maintenance. Long term, Subaru (like most makers) can point to the service intervals and say "You didn't follow the schedule, we told you so".

Luckily, several people have reported good results with a supplemental water/meth system. Run extremely light settings and refill the washer jug every few fill ups and it's almost as good a port injection fuel system. The turbo guys also get an added benefit of extra charge cooling.

There are a few ways to help nip the issue, but really, port injection is the ONLY way to keep the valves clean.

 

If anyone is interested...... I am now the proud owner of a 2019 Limited 3.6R. I decided it was not worth the worry on the Direct Injection.

 

My first post here and looking for new car for my fiancé to replace her 2006 Acura TL with 204K miles which runs fine, burns no oil, no rust, she just wants something new.

I’ve lurked here a bit but totally agree with you. For her especially I want nothing to do with DI unless it’s the Toyota DS-4 dual system for long term trouble free miles. This is a big problem for sure with no good resolution. I do not trust Subaru to get this right either for the 2020 Outback without the use of the DS-4 system (like on the BRZ/Toyota 86). They didn’t use it on the Ascent so I doubt it’s gonna be used on the Outback but direct injection will be. Also if the famous oil consumption issue is still present in some form you could potentially have more fuel (um carbon buildup) to the fire. A warranty nightmare for sure.

Some of these DI motors are having issues by 30K miles. This is our new regular accepted maintenance for a modern motor? NO way! A modern motor with regular oil, filters, plugs, maybe water pump for good measure should go 200K without being opened up IMHO.

Anyway we drove the 2.5 and 3.6 Outback Limited’s, new Forester and RAV4 Limited’s. Forester is straight DI so no go but we wanted to try it. Nice more modern interior than OB but I felt noisier than the 2.5 OB and busier over uneven surfaces. Very short center arm rest and cup holders to far back. 2.5 OB was what I would call pleasant like an old friend. Decently quiet until accelerated hard then noisy and slow. Remember Acura TL with velvety smooth V6 is what she is used to. Next up 3.6R. Really nice ride, quiet and smooth and more than enough oomph for on ramps, passing, etc. without having to think twice. Yup, old design motor but no DI, no turbo, no intercooler and all the associated paraphernalia that goes with those items. So the 2019 RAV4 Limited (full disclosure I work at this Toyota dealership) is really nice in and out. I feel they have done a very nice job on the redesign and obviously I can get a terrific price. The new 2.5 motor also uses the DS-4 dual system. Great right? Nope. Very noisy engine, really thrashy sounding on hard acceleration. Transmission did some funny stuff (I notice she doesn’t and she also didn’t notice the Subaru was CVT). Interestingly there is no hood insulation on the RAV. We will wait to drive the Hybrid version which should arrive late March/early April hopefully. Most early reviews say it more refined feeling, its faster than the gas model, has more overall HP, it’s CVT is superb and it’s mileage is exceptional 41/37/39. Same noisy motor though and that could be a deal breaker.

Long story short we liked the Outback Limited 3.6R best even if it’s at the end of its run and perhaps a bit dated. Fuel mileage is very similar to her TL but the Acura requires premium and she’s tired of paying the difference. Also looking at the Fuelly gas mileage site and reading lots of reviews and Consumer Reports the 3.6 mileage penalty over the 2.5 is about 2-3 mpg. Not bad. Consumer Reports quote “the 3.6 transforms the car” and I think we agree.

Skidad in MA

 

I was going to install water meth on my Ascent but I am concerned it would cause warranty issues. You could easily set it up so it only goes on under higher boost and doesn't mess with fuel trims.

 

Carbon fouling at the intake valves on a DI engine would be so much less of a problem if we didn't have to contend with the oily sludge from the PCV system or the soot from the EGR system.

Other than those two systems there is a very slight amount of oil that will drop in from the turbo seal or the intake valve stem seals. You could almost cope with those if you SeaFoamed the intake manifold every other oil change interval to wash away some of the residue.

With the PCV system you could install a good oil catch-can and drain the thing out at each oil change interval; That is just going to be whatever oily mist that comes out of the heads/crankcase.

The EGR system is more complicated; Its hot exhaust gases that are loaded with partially burnt combustion products and soot. If you have ever taken apart an EGR valve because it was plugged up with soot, then you can see what crud gets pumped back in to the intake manifold from that system.

Some diesels have EGR filters to reduce the amount of soot. I don't know why they couldn't do the same thing with a gasoline engine and maybe to combine a heat exchanger to cool down the EGR gases... It just seems like we are stacking inefficiencies on top of inefficiencies with EGR to rob the engine of performance for the sake of reduced NOx... There are other ways to reduce NOx from high temperature combustion (better catalysts, air injection in the exhaust manifold before the catalyst to complete combustion with oxygen rich air, urea injection, etc..).

It's a "pig in a poke"... they build all of these systems like EGR and PCV in to a vehicle to reduce emissions but for those systems to operate efficiently they constantly have to be fiddled with. Just about every car with less than 100,000 miles on it is going to need an EGR valve replacement because it gets plugged up. Now every DI engine will need a walnut media blast somewhere in that 100,000 mile period.. All are guaranteed revenue for the stealerships as it will usually happen outside of the warranty period (even with extended warranties that might still be honored on emissions systems in certain states).

So instead, you will get that check-engine light at 60,000 miles and maybe you will pull down the code to see its an EGR message. Maybe you will just suffer from poor performance because of carbon fouling on the intake valves. The engine will run very inefficiently, it will pollute and we will make-do for another 40-50K with the check engine light illuminating our dashboards.

 

^^^^ +1 and all those xtra trips to the dealer, the xtra parts produced and shipped to replace the bad emissions parts, plus any inefficient operation of the car means.........wait for it........additional emissions!

 

This is some good discussion! I have been researching the FB2.5D engine and it appears that some 2019 Forester owners have had isses with the PCV, see link below:

('19+) - 2019 - died on the highway - dealer said...

My wife was coming home from work and she looked in the mirror and could not see out the back as there was a cloud of WHITE smoke. It was dangerous as people behind her couldn't see and it was causing mayhem on the highway. There were no warning (check lights) on the dash. When she pulled over...

www.subaruforester.org

On my 2012 Hyundai Accent GLS with the 1.6L GDI engine it is recommended to change the PCV valve every 30,000 miles. Thankfully the part can be had for around $10 and it is extremely easy to change out. For this engine specifically a faulty PCV valve is among the top contributors to engine failure. It appears that the same can be said for Subaru's GDI engines.

 

Interesting you bring that up. I have been reading the Ascent forum and there were two engine failures described there that SOA attributed to PCV valve malfunction. link https://www.ascentforums.com/threads/engine-has-let-go.8557/page-2

 

Good find, I was just on my way to researching FA2.4F engine issues but you beat me to it. I don't have much personal interest in that engine simply because I do not see myself acquiring a vehicle with it. That being said it is important to keep track of any and all negative trends.

I am not sounding the alarm just yet on any Subaru GDI issues, just keeping abreast.

 

So which PCV part is being used in the Outback? Do we know?

 

We will wait to drive the Hybrid version which should arrive late March/early April hopefully. Most early reviews say it more refined feeling, its faster than the gas model, has more overall HP, it’s CVT is superb and it’s mileage is exceptional 41/37/39. Same noisy motor though and that could be a deal breaker.



Skidad in MA
[/QUOTE]

@Skidad: I also am comparing Gen 5 & Gen 6 outback to RAV4 Hybrid. The R4H seems like it is pretty comparable to the OB and superior in a variety of ways to the standard R4. For me the R4H's 40 mpg is a big attraction. By now I imagine you have driven the R4H. If so, I (we) would love to hear your analysis.

 

The 2.5 engine now being DI - is it a real concern?
Will it be less reliable than the previous gen 2.5L engines?

 

I am most likely going to be trading in my 2018 Limited Outback within the next 6 months and I am weighing my options because I intend to drive my next vehicle up to 100,000 miles within the following two years. It goes without saying that I will be getting an extended warranty and I do my best to keep maintenance records on hand as well as document them on MyCarfax.com. If Subaru was REALLY smart they would have developed a system akin to Toyota's D4S system with dual injection which Toyota permitted them to use with the BRZ.

I am concerned about Subaru's switch to direct injection engines across the board but no so much so that I will exclude their vehicles, namely the Outback, from my consideration. I have a 2012 Hyundai Accent with a GDI engine that has a track record among owners as being relatively problem free, some reporting having gone over 200,000 miles doing regular maintenance without issues. I am hoping Subaru's FB2.5D will be similar at least for the 100,000 miles I would be driving it.

Turbo engines with GDI are the main concern but their issues can affect non-turbo GDI engines to a lesser extent.

 

no

 

Not "less reliable"... but may need an occasional intake-valve cleaning like all other DI engines.

 

Use quality fuels that have top quality additives like Chevron or Shell. That goes for any engine...not just DI engines.

 

So I emailed Subaru about my concerns with their direct injection engines:

I have owned 4 Subaru Outbacks and will be looking to lease or purchase a 2020 Subaru Outback within the next six months. I am incredibly concerned by the fact that Subaru now only offers engines with direct injection. There have been major issues reported that are inherent to this engine design to which there is no permanent solution. Are issues such as carbon buildup on intake valves something that Subaru would address in or out of warranty?

RESPONSE:

Glorious and Triumphant Outback King:

Thank you for your email, questions and concerns and although engines have come a long way. Subaru stands behind it product as long as there the vehicles have been maintained as scheduled and the repair falls under the warranty you should not have any worries.

You can always contact any of our service department technicians at your local Subaru retailers with questions and or concerns regarding service and repairs. I hope this information was helpful?

Sincerely,

Karen Robinson
Subaru of America, Inc.
Customer/Retailer Services Department
1-800-SUBARU3 (1-800-782-2783)
Service Request Number: 1-48225061993

 

So I emailed Subaru about my concerns with their direct injection engines:



RESPONSE:

Glorious and Triumphant Outback King:

Thank you for your email, questions and concerns and although engines have come a long way. Subaru stands behind it product as long as there the vehicles have been maintained as scheduled and the repair falls under the warranty you should not have any worries.

You can always contact any of our service department technicians at your local Subaru retailers with questions and or concerns regarding service and repairs. I hope this information was helpful?

Sincerely,

Karen Robinson
Subaru of America, Inc.
Customer/Retailer Services Department
1-800-SUBARU3 (1-800-782-2783)
Service Request Number: 1-48225061993

A completely useless response, but as expected. IMO, at least.

 

@lfdal posted this in a couple of other threads. It was making the rounds on a few forums when the DIT WRX came out.

Copy/paste issues. Subaru’s (supplier’s?) patent for engine breather apparatus mentioned earlier in this thread is in the last post here:

2020 Outback, and the 2.4 Turbo Engine

Does anyone know if the rumored turbo engines that will be in the NextGen Outback will require premium gas? I am seeing this for many manufacturers, like Volvo. In my area, North Carolina, premium gas costs about $.50 more per gallon. This is an absolute showstopper for me! I post this because...

www.subaruoutback.org

And just a few posts above his I posted a slightly better technical response from Subaru that Robert Mauro was able to get.

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.

From

Question on direct injection

Any new ascent owner here did any preventive maintence by install oil catch can or air oil separator? I wonder the one for 15 and up WRX will work with Ascent.

www.ascentforums.com

It’s been a while so I want to read that patent document again. I agree Toyota’s D4S would’ve been the way to go.

 

Unfortunately the better response from Subaru still doesn't totally address the problem. Read here:

Intake Valve Deposits in Gasoline Direct Injection Engines

I asked my subaru service department about my wife's forester XT. They recommend an induction cleaning at 60k. It's basically one of those sprays you spray in while the car is running at around 2000 rpm. A good reference to using one is here, and seems to be the most popular product I can find. :

How To Use CRC GDI Intake Valve Cleaner » NAPA Know How Blog

Unlike fuel additives, using GDI intake valve cleaner is a little more involved. Here’s how to use CRC GDI IVD® Intake Valve & Turbo Cleaner.

knowhow.napaonline.com

The fact a Subaru dealer recommends this cleaning indicates not all is solved with the above referenced statement from Subaru

 

The fact a Subaru dealer recommends this cleaning indicates not all is solved with the above referenced statement from Subaru

Dealers recommend all kinds of bleep that you don’t need.

 

BMW ran into issues with carbon buildup in the N54 inline six cylinder with direct injection. And it was attributable to the PCV system, specifically oil separation from the gases re-introduced to the intake tract. In the follow on to the N54 engine, the N55, BMW has seemed to solve that. The N55 has been around since the turn of the decade, at least, so other manufacturers have had the opportunity to see both the problem and potential solutions. Whether they've heeded that lesson . . . ; -)

 

I had someone from BMW NA (located very close to SOA's HQ) tell me that if port injection is a cost of '1', solenoid direct injection is a cost of '3', and piezo direct injection is a cost of '9'. BMW used piezo-electric direct injectors in the N54 engine because they could control multiple fuel pulse events per combustion cycle (based on load/RPM), They used the piezo injectors to spray fuel when the exhaust valve opened, before the eninge was up to temp, to heat up the catalytic converter to improve its efficiency. Bosch introduced a solenoid direct injector later that allows the same benefits as a piezo DI system and that's in common use in BMW engines currently.

 

What folks seem to be missing here is that the type of fuel has really no effect on carbon buildup on the intake valve; the design of the injector has limited effect on the buildup of carbon on the intake valve. Fuel does not hit the back of the intake valve a direct injector systems...only air. Also, when exhaust gas recirculation is used for emissions than those fumes are sent back to the intake side hence the source of the carbon on the back of the intake valve. Incomplete combustion can also contribute to carbon buildup when the intake valve opens...I'm sure Subaru engineers have done their best in this area but there is no such thing as 100% complete combustion.

Modern synthetic engine oils can help with carbon buildup but it is really not the solution. This video is sponsored by Valvoline but has some information that is useful:

Here is another video on why systems using a port injector in addition to the direct injector is the way to go:

.

The current Subaru direct injection engines don't really have enough miles or quantity in the field at this time to see if they have no issues with carbon buildup. The first direct injector engines were in the 2017 Impreza...time will tell. Fortunately, cleaning out the carbon does not need an engine teardown to fix. Many older German cars have had these issues for years and the cleaning process is well known.