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Sahuarita, Arizona USA 2018 Forester Limited
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Discussion Starter #1
Just wondering if anyone is experiencing engine oil dilution (gasoline in oil) with their 2019 direct injection FB25 engine? Oil dilution seems to be a somewhat common problem with GDI engines, some worse than others.
 

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2017 Forester XT Touring CVT
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236 Posts
Completely agree with @adc;

personally i have the turbo fa20 direct injection. no issues for almost 60K. every other oil change get an analysis.
 

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2018 FXT-T CVT / 2014 VW Passat TDI SEL
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It's worse with Direct injection due to poor ignition when cold. But as mentioned, so long as the engine routinely gets up to temp where the oil itself hits operating temps the fuel will evaporate out. I had one of my 7 or so past direct injection vehicles have a problem with fuel contamination and that was as a result of a leaking hpfp. Rings on that engine we're toast before 40k miles. Blackstone caught the fuel dilution before I knew there was a problem. Shortly after that it started drinking oil.
 

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Sahuarita, Arizona USA 2018 Forester Limited
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Discussion Starter #5
I agree that some oil dilution is present in all engines, even port-injected. But it rises to the level of being problematic in some direct injected engines.

I also agree that oil analysis is the best way of knowing the severity of the problem, if any. However, some GDI engine owners are noticing oil dilution by a rise in the oil level on their engine oil dipstick. Anyone noticing this telltale sign on their dipstick?
 

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2018 FXT-T CVT / 2014 VW Passat TDI SEL
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I doubt that's the case. In my case rings we're destroyed shortly after a dilution of just 4%. Enough fuel to impact a reading on the dipstick that is measurable would be much higher than that. Probably closer to 10%+ and the engine would already be toast.

Edit:. Correction, it was only at 2%. They changed the hpfp after that sample
 

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2019 Forester Base CVT
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190 Posts
It's a very common problem with the Honda 1.5 Turbos from the past 2-3 years in Civics and especially CRVs. Just Google "gas in oil Honda CRV" and you'll have a summer's worth of reading. Our son has the Civic Turbo and he watches his oil level rise on the dipstick up to an inch between changes as it dilutes with gasoline. No cure from Honda.

Good news: We bought a '19 Forester in October and just had the oil changed last week at 3,500 miles. Mostly trips of 25-200 miles, since we have a runaround car for in town. I checked the oil very frequently and it never moved from just about 1/16 inch above Full. No smell of gas. Surprisingly, the oil was still almost as clean as new. Many people complain of dirty oil in GDI engines.

FWIW - We also have a 2013 Kia Soul Base 1.6 Automatic with 90K miles (and GDI). It is still running like new and uses almost no oil - synthetic only. No fuel in the oil that I can tell or smell.

.
 

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2017 Forester XT Premium
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554 Posts
This is the only issue I have with this car.. My first xt, bought new, same year, did not have this problem.. It had a cvt leak, couldnt fix it , no spares available, they gave me another car..
THIS car, the second XT does have oil dilution with gas, has from day one, no need for a oil analysis to tell me that, you can smell it just walking up to the car.
The oil level never rises or falls, stays right where its supposed to. everytime I make an appointment I am fed the line we will call you when the subaru rep is here, it never happens.
I have 16 k miles on the car, If and when the engine deteriorates to the point of burning oil, from the first puff Of smoke I see, the car goes, let someone else deal with it and I tell ya, I dont feel bad about that..
 

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2001 Forester
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882 Posts
Gasoline presence in oil is caused by couple of things. Short trips, ie driving less than 5 miles everyday. I see a lot of drivers around where I live that drive 2-3 miles for the commutes to work. The other thing that causes fuel to show up in the oil is idling the engine in the morning to warm up the engine. When a engine is cold it is running in what is called open loop. This results in extra fuel being injected into the engine until the engine is warm enough to enter Closed Loop. In other words, Open Loop is similar to the old days of using a choke on the carburetor to compensate for poor combustion.

Driving less than 5 miles does not always result in getting the engine warm enough to get the ECU to change from Open Loop to Close Loop.

It would be interesting to collect data from owners that have this oil dilution problem: 1. How far to you drive, 2. How long do you idle the car?
 

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2004 FXT / 2020 Outback Onyx XT
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Anyone interested in getting a uoa to see the amount of actual fuel dilution should use a lab thats check fuel by Gas Chromatography, like Oil Analyzer’s Inc.

Blackstone’s fuel reading is an estimate based on flashpoint and a GC reading will always come back higher. There are many uoa’s on the same sample posted on nasioc in the 2015+ WRX forum and there may be some comparison uoa’s in the uoa sticky in our 2.0DIT forum as well. 2-4% isn’t unusual in the DIT but I haven’t see any from the new Foz engine yet.
 

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2018 FXT-T CVT / 2014 VW Passat TDI SEL
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Gasoline presence in oil is caused by couple of things. Short trips, ie driving less than 5 miles everyday. I see a lot of drivers around where I live that drive 2-3 miles for the commutes to work. The other thing that causes fuel to show up in the oil is idling the engine in the morning to warm up the engine. When a engine is cold it is running in what is called open loop. This results in extra fuel being injected into the engine until the engine is warm enough to enter Closed Loop. In other words, Open Loop is similar to the old days of using a choke on the carburetor to compensate for poor combustion.

Driving less than 5 miles does not always result in getting the engine warm enough to get the ECU to change from Open Loop to Close Loop.

It would be interesting to collect data from owners that have this oil dilution problem: 1. How far to you drive, 2. How long do you idle the car?
Closed loop is a feedback loop of measuring the AFR sensors reading, MAF and MAP sensors all to adjust target injector flows. Open loop is taking the AFR sensor out of the equation so it's relying on the MAF and MAP sensors along with fuel trim corrections it's applying based on learning from the feedback while in closed loop.

Open loop is not deliberately adding additional fuel to compensate for poor combustion. Open loop is just needed when closed loop fueling isn't possible due to response time or cold sensors not reading accurately.

In the case of cold starts it is in open loop because of cold sensors. It runs at higher rpms and richer fuel mixtures not because that's what open loop fueling is telling it to do by nature, bit rather because that's the target idle and fuel at those temps to quickly warm up exhaust gasses to get sensors and cats warm.

You also switch to open loop fueling when you go WOT.
 

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2015 Subaru Forester 2.5 Lineartronic CVT TR580
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I am not scared of oil dilution as much as I am scared of carbon build-up? I dont know what to think cause its a boxer engine after all.
 

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2018 FXT-T CVT / 2014 VW Passat TDI SEL
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Carbon buildup can be kept under control with periodic top end cleaning applications like Subaru's carbon clean or CRC intake valve cleaner every other oil change. It's just new maintenance that didn't need to be done before at the total cost of 20 dollars if you DIY every 10k miles or so.
 

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I used them every oil change on my GM vehicle. Still had build up enough at 75k miles that the valves required cleaning.

You also cause a secondary issue by cleaning often. The deposits are hard as stone. When you wash them off the valve they tend to lodge in the cylinder wall. Not really something you want to do on a Subaru considering we don't know yet if oil consumption is an issue.

The GM engineers on our forum did not suggest ever using spray cleaners like that. Intake manifold removal and blasting+vacuum is best method and safest to prevent other issues.

Hopefully Subaru has done some baffling or PCV system modifications to prevent this for at least the first 100,000 miles. I haven't even looked at the Forester to see how detailed that process would be.
 

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2018 FXT-T CVT / 2014 VW Passat TDI SEL
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For transparency how did you determine how much buildup there was at 75k miles? What product did you use? The CRC intake valve cleaner softens the carbon buildup so what is removed is not hard...it wouldn't be removed if it was still hard as that's not how the product works, chemically.
 

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1. I pulled the intake manifold and looked. For most vehicles you can feel the misfires on cold start. On a boxer engine the damn thing already feels like this on a new vehicle so not sure that's gonna be felt.
2. Seafoam was I used. Sucked into a breather tube into intake manifold.
3. As with seafoam and CRC there is a huge issue and it's the reason they don't work. Contact time. With GM top end cleaner it took 3-4 hrs of the valves being completely submerged valves to dissolve the hardness material.

Not to mention when spraying seafoam and CRC, you have another big problem. You don't know if the valves are open or closed. An open valves will allow the cleaner to run into the cylinder which removes all contact time on the valve. Again, for those that have done the cleaning, these items become apparent.

A catch can won't work. An oil separator might but you need someone to design them to maintain correct vacuum.

I just came from a 17 CRV. Honda built baffles into the valve cover to prevent this. Before mine was totaled we were trying to determine if they were the cause of oil dilution.
 
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