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2015 Forester XT CVT
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Discussion Starter #1
HI
Most all DI engines will have carbon buildup (except for those with dual port/DI) so every 30-45K you can choose to have a carbon service done for about $130 to clean off the valves...no biggie and it works very well. The Subaru dealer will do it to.
I have not heard this as actual fact.Can you give any references? I agree that most DI engines do accumulate carbon but the amount and impact on the performance or efficiency does not seem to be well documented. Is this actually a service that is on the recommended maintenance schedule? It does not appear here in Canada at least not for my 2015 XT. I have seen comments about some in Australia but little about the actual result of the work. The only effective method of cleaning carbon off seems to be walnut blasting and that is more expensive than $130 so far.

I have been concerned about carbon build-up on my XT since I heard of the problem but there does not appear to be any consistent data as to how to reduce it or if it will become a problem. I expect that Subaru is keeping quiet about what they know because it could reduce sales.
 

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1997 ford f250
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28 Posts
Do you think carbon buildup will be an issue with the new 2.5 DI motor?

The reason I ask is, now that I'm retired most of my miles are short distance (3 to 4 mile) around town trips and I'm concerned with carbon buildup with the new DI motor. I know that short distance trips are hard on any motor, but probably more so with DI.
 

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2019 Forester Touring
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595 Posts
Yes, carbon buildup is a characteristic of direct injection engines. However, it’s nothing that can’t be dealt with. And, yes, short trips encourage a faster rate of carbon buildup as compared to long highway trips.

Just think of the cleaning as a periodically required service.

AFAIK, no manufacturer has been able to get around the eventual carbon buildup without adding other components, such as dual-injection systems.

I bought a 2019 Forester Touring... I didn’t see it as a show stopper.
 

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I wouldn't worry about it. There is a handy new blue light that lets you know your engine is still cold. If I were in your shoes I would take my time on my short trips, letting the car warm up fully before driving and taking extra care to be gentle.
 

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2019 Forester Touring
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I suspect the answer is “no”.

Batteries, tires, etc. aren’t covered because it’s considered these items are normal wear/expendable items, and I’d be surprised if carbon buildup didn’t fall into this classification.

Of course, nothing prohibits Subaru from including it if it chooses to do so, if the issue becomes an engine performance factor affecting a disproportionate amount of Foresters later on.
 

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2010 Forester Diesel 6MT
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793 Posts
Crud build-up on the intake valves is a 'feature' of direct injection engines. It comes from the EGR and/or PCV systems feeding into the intake manifold/pipes. In the old port-injection, throttle-body injection and carburettor systems, the fuel (petrol) itself acted as the solvent to (generally) remove these deposits.

One way fix is to have another injector in the intake manifold which periodically squirts fuel in to clean the inlet valves/ports. This sort of defeats the whole purpose of having direct injection, but anyway, the other way is to have periodic cleans of the inlet manifold using a suitable port/valve cleaner.

CRC produce a cleaner specifically for DI engines. If you (or your dealer) uses Subaru Upper Engine Cleaner (SUEC) this I suspect is likely to do the job for you. It's quite simple, the stuff gets squirted into the inlet manifold whilst the engine is running. A bit of revving, a bit of soaking and perhaps some driving and the job's done.

I asked my local dealer who indicated they didn't think the engine has the extra injector. So you are likely to require a periodic clean of the inlet ports/valves. My local dealer indicated they run SUEC through cars they service as a matter of course. SUEC is quite highly regarded, it seems, and a lot of other people use it on other makes & models too.

If you want a bit of an intro to it all, see the video below which explains it at/near the beginning- just be warned, John has a rather abrasive, if also rather entertaining and informative style.

The truth about oil catch cans: Should you fit one to your car? | Auto Expert John Cadogan
 

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2019 Forester Limited CVT
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42 Posts
My only concerns with a Subaru are, added maintenance/expense of the DI motor carbon buildup over time with 3 mile short in town driving trips (I'm retired)
Could someone go into a little more detail about this, please?

This is the second post about this subject inferring that short trips are the main negative regarding this. When I buy one it will be used mostly for my daily 60 mile work commute; which makes it seem not that big a deal. Is that correct?

Thanks
 

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2019 Forester Touring
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595 Posts
With direct injection, carbon buildup is going to happen. It’s just a question of how soon and how often.

And, to some extent, the rate of carbon buildup is directly related to how long of a period that the engine runs. Engines that are run shorter distances, allowed to rest for an extended length of time (hours .vs. minutes, as an example), then run for another short distance are going to see carbon buildup on the intake valves much faster that the same engine run for an hour at the time, a period of rest, than another long running period.

Why? Oil temperature, for one thing. Hotter oil cooks off moisture. Short “run” periods never get the oil warm enough to cook out the moisture. Higher moisture contented oil residue coagulates on the intake valves, causing oil buildup.

But, that’s not the only reason. Engines that have dual injection systems, or systems that inject the fuel directly into the intake manifold (above the intake valves) gain the benefit of having the fuel spray above the intake valves act as a cleaning solvent, helping dissolve the carbon...ie., preventing carbon buildup. There is no such cleaning on direct injected engines.



There are endless explanations of these conditions, as well as explanations of how different injection systems function all over the internet. Therefore, there’s no need to reinvent the wheel here...

Google “direct injection carbon buildup” and marvel at all the explanations, in written, verbal and video presentations.
 

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With direct injection, carbon buildup is going to happen. It’s just a question of how soon and how often.



And, to some extent, the rate of carbon buildup is directly related to how long of a period that the engine runs. Engines that are run shorter distances, allowed to rest for an extended length of time (hours .vs. minutes, as an example), then run for another short distance are going to see carbon buildup on the intake valves much faster that the same engine run for an hour at the time, a period of rest, than another long running period.

This describes me to a T. So should I avoid the Forester and look at something else?


Sent from my iPhone using Tapatalk Pro
 

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1997 ford f250
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The main issue for me not buying the Forester Sport yet is the potential for carbon buildup on the new 2.5 DI motor on short trips in a cold climate area. If I decide to buy the car, I will get an engine block heater installed.

In searching this issue with the Crosstrek 2.0 DI motor, it doesn't seem to be an issue (yet?), when did the 2.0 motor get DI? Or is the motor still too new for carbon buildup to happen?
 

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2019 Forester Base CVT
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189 Posts
The main issue for me not buying the Forester Sport yet is the potential for carbon buildup on the new 2.5 DI motor on short trips in a cold climate area. If I decide to buy the car, I will get an engine block heater installed.

In searching this issue with the Crosstrek 2.0 DI motor, it doesn't seem to be an issue (yet?), when did the 2.0 motor get DI? Or is the motor still too new for carbon buildup to happen?
Although there were some problems with GDI early on, most (not all) manufacturers have learned lessons to prevent catastrophic failure. We have a 2013 KIA Soul Base 1.6 Automatic with GDI. It has 87K miles and is running like new. I've used synthetic oil almost every change since the synthetic emits less "fumes" when heated, therefore reducing buildup in the PCV/Intake tract.

Contrary to what some folks say, running a bottle of Techron or Seafoam thru it is NOT going to clean off the valves. The fuel is injected downstream and never touches the intake valve on the "outside" face where buildup occurs. Many KIA folks run Catch Cans to supplement the PCV, but there are lingering questions about how that affects the warranty. I still think synthetic oil is good preventative maintenance for the carbon buildup issue.

If you think about it, almost all diesel engines the past 30 years have been running on the exact same principle as GDI up to the point of ignition. They are also direct injection, with PCV fumes being sucked into the intake tract over intake valves that never get "washed". There are a lot of diesel trucks out there with 300K-400K-500K miles running strong. So, I think the manufacturers can design around that problem.

Question is: Did Subaru do its homework? Let's hope so. I have a new 2019 Forester base model sitting in the garage with just 800 miles on it. I'm hoping to hit 200K miles someday.
 

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'19 Forester LTD CVT
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@ryan_calif - Well, hopefully they address the fouling issue with a fix and a usb for those of us that might be affected.
There never will be a fix, it's an inherent part of direct injection and shared with every direct injection engine in the market. Walnut blasting the valves will just become a routine service item on direct inject engines.
 

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'19 Forester LTD CVT
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@ryan_calif - Well, hopefully they address the fouling issue with a fix and a usb for those of us that might be affected.
There never will be a fix, it's an inherent part of direct injection and shared with every direct injection engine in the market. Walnut blasting the valves will just become a routine service item on direct inject engines.
 

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There are other less invasive services that perform very well and I have experienced and can vouch for. BG is a great quality product and dealers around here charge about $130-$150 for the full cleaning. It does work!


 

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2019 Forester Base CVT
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Diesel engines work on almost the same principle as DI engines up to the point of ignition. They also have Direct Injection that does not "wash" the intake valves. They also have PCV fumes being sucked into the intake tract and past the intake valves. They've been doing this for the past 30-40 years. I don't hear any big hoopla about diesels self-destructing (aside from the GMs in the 80s - LOL).

Point is - with proper design, DI engines can last as long as Port Injection engines. I drive a 2013 KIA Soul 1.6 with GDI and it is coming up on 90K miles. Still runs like new and used not a drop of oil in our last 1,700-mile trip. I use synthetic oil because it emits far less vapors when hot, resulting in fewer deposits on the intake valves. DI in and of itself is not a strong reason to blacklist any car. Except maybe a Yugo, if they ever come out with it.

I would think (hope) that Subaru has done its homework and researched the DI engines from other manufacturers over the past several years as it was developing the new engine. I'm sure they don't want to have to pay to replace engines.

Regardless - I bought the 7-Year / 100K-Mile Bumper to Bumper warranty with Zero Deductible, so I don't have to worry about it - Subaru does. LOL


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Point is - with proper design, DI engines can last as long as Port Injection engines.

I believe it's more "with proper servicing" DI engines will probably last longer than other engines ;-) A part of my Triton diesel ute service schedule includes decarbonization.
 
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