Fuel dilution DI vs. PI

[OilUzer]

question regarding more fuel dilution with DI engines vs. PI.

I read that with DI engines, fuel is directly sprayed into the combustion chamber and can wash past the rings and into the oil sump as opposed to the manifold in PI engines.

big picture you would think fuel is fuel (in the combustion chamber) no matter how it got there.
Is it the form of the fuel we are talking about? In case of port injection it is more of a vapor or mist (mixed with air) as oppose to DI.

wouldn't the fuel immediately evaporate/vaporize as soon as it's sprayed in a very hot combustion chamber? How can it "wash down" the rings and cylinder walls and get into the sump? Hard for me to picture that when the engine is at operating temperatures.

Is fuel dilution an issue only at cold startups? How about when the engine is hot?
Or is there another path for the fuel for example talking long term and as a result of potential IVD.

 

[Blinker]

There are a lot of well written articles from oil companies, additives companies, and service industry shareholders, that all go into detail about PI vs. DI and can answer all your questions.

 

[JimPghPA]

Actually, at least with Honda, it is the engines with the combination of turbo-charging and direct injection that are having problems with fuel getting past the pistons and into the oil.

The normally asperated 2.4 Liter with direct injection only had a little bit of fuel getting into the oil. Not enough to increase the reading on the dip-stick in most of them, but often enough to make the oil have a slight smell of gasoline that smelled similar to oil from a lawn-mower.

The turbo-charged 1.5 Liter with DI that makes a few more HP than the 2.4 Liter has problems with enough fuel getting into the oil to increase the level on the dip-stick, especially if the vehicle is often driven only short distances where it never gets the oil hot enough to boil off gasoline from the oil. This problem is made even worse if the often short tripping is in cold weather.

Because many vehicle manufacturers are now using smaller engines with turbo-chargers and DI, people seam to only associate the fuel in the oil problem with DI, but the increased pressures in the cylinders in a turbo-charged engine seams to have something to do with the problem. Also manufacturers are always trying to squeeze every last amount of fuel economy from these engines and are using low friction piston rings that do not help this problem.

 

[PimTac]

One thing that adds to fuel dilution is the engines run rich at a cold start to get the engine warmed up quicker. When a person short trips the car this will add up over time.

 

[doublebase]

What’s the pressure on a direct injector compared to a port injector? 50psi to 500psi? I imagine that has a lot to do with it, plus the high pressure fuel may wash oil off the walls, losing some of that seal...then the fuel can get through easier. I’m reaching here but I don’t think I’m that far off.

I have smelled that fuel in the oil sometimes on direct injection engines. The first time you own one, it takes a bit to get used to.

 

[spasm3]

High pressure spray right into the combustion chamber, not the port, higher compression. Most modern engines have the top ring land much higher on the piston.

All that together causes the issue, I also wonder like PimTac mentioned above , if at the higher compression ratios, they keep the stoichiometric ratio on the rich side, to keep Nox down.

It seems to be a problem if you short trip. If you get the engine oil up to temp every trip, you probably don't have a problem. My mazda is short tripped. I discovered the fuel dilution issue, after an oil change. Each day, the level on the dipstick was higher!

 

[PimTac]

I have smelled that fuel in the oil sometimes on direct injection engines. The first time you own one, it takes a bit to get used to.

It reminds me of the old carburetor days.

 

[spasm3]

It reminds me of the old carburetor days.

Thats probably true! Carbs really were not that accurate cold. You adjusted it rich enough to start, and that was probably really rich.

 

[JimPghPA]

It would be interesting to see data from test of different oils ability to provide proper protection in engines at different levels of fuel dilution. Blackstone reports post normal amount of fuel as < 2 % but on a Honda CR-V owners forum there was a turbo-charged DI engine with 9 % of fuel in the oil. Does that much fuel cause the oil to loose the ability to protect the engine properly? There are of course other variables such as these small turbo-charged engines having higher compression and HP causing more pressure on crank journals, and the crankshaft bearings, and the higher RPMs these smaller engines run at. This sounds like a whole category that should have a name and numerical numbers assigned to different oils depending on there performance in these conditions. There should be some numerical ratings for oils so people can chose the oils that perform well in these conditions, and probably meats some industrial set minimum for these type of engines regarding these conditions.

I do not know who makes decisions regarding the naming and types of test oils should meet, but this is something they should consider.

 

[B1974]

question regarding more fuel dilution with DI engines vs. PI.

I read that with DI engines, fuel is directly sprayed into the combustion chamber and can wash past the rings and into the oil sump as opposed to the manifold in PI engines.

big picture you would think fuel is fuel (in the combustion chamber) no matter how it got there.
Is it the form of the fuel we are talking about? In case of port injection it is more of a vapor or mist (mixed with air) as oppose to DI.

wouldn't the fuel immediately evaporate/vaporize as soon as it's sprayed in a very hot combustion chamber? How can it "wash down" the rings and cylinder walls and get into the sump? Hard for me to picture that when the engine is at operating temperatures.

Is fuel dilution an issue only at cold startups? How about when the engine is hot?
Or is there another path for the fuel for example talking long term and as a result of potential IVD.

You are right about when it's sprayed in a hot combustion chamber part.

It's when the engine is cold especially in below freezing climates that the fuel condenses on the cylinder walls and gets into your oil. Direct injection engines usually have higher compression ratios then port injection, it's the higher cylinder pressure that pushes more unburnt fuel past the piston rings.

Turbos will increase this even more.

 

[doublebase]

It reminds me of the old carburetor days.

Yup, definitely.

The first time I changed the oil on my 2018 Silverado we all were standing around kind of just looking at the oil (I’m a tech, I work with techs), well actually I’m not a tech anymore I’m an automotive instructor (working with four other instructors) and we all looked at ourselves and were like, what’s that smell? Is that gas? And of course we got a cup and poured a little into it and took a sniff. And then of course I had to hear...this shouldn’t smell like this, take it back, it’s under warranty. Haha.

I did end up taking it back, but two years later at 52,000 miles, when I grew tired of having random misfires and being told...you probably need injectors, and it’s not covered under power train warranty because it’s electrical. Sold it back to the dealer for $24,500. I’m thinking...probably could have received maybe $26,000 in private sale. Then again I did list it for a month at that price and didn’t receive one single call or email.

 

[demarpaint]

I still find it amusing. In the quest for more power and better fuel economy the auto industry turned out a problem technology, then they turn to the oil industry to try and fix it. Call me an old timer, I am. I'll take EFI over DI any day of the week. I'll give up a few HP and mpg, I have no problem with that. Like most people I transport people and occasionally equipment from point A to point B. I don't race, and my vehicles have more power than I can use. Yea the technology is getting better, but after reading these kinds of threads almost on a daily basis for several years now, imo the tech still isn't dialed in yet.

It's getting better, but given a choice for me, it's EFI. FTR I love and own new technology.

 

[4WD]

It reminds me of the old carburetor days.

Yep, I recall the 4 bbl carbs did it too …
And smelled gas in oil when we had a 2013 Pentastar (PI) and now have a 2020 and don’t smell it
My Chevrolet 5.3L L83 DI = The oil never-ever has a gasoline smell …
Dots don’t always connect the same for all vehicles & drivers …

 

[PimTac]

I still find it amusing. In the quest for more power and better fuel economy the auto industry turned out a problem technology, then they turn to the oil industry to try and fix it. Call me an old timer, I am. I'll take EFI over DI any day of the week. I'll give up a few HP and mpg, I have no problem with that. Like most people I transport people and occasionally equipment from point A to point B. I don't race, and my vehicles have more power than I can use. Yea the technology is getting better, but after reading these kinds of threads almost on a daily basis for several years now, imo the tech still isn't dialed in yet.

It's getting better, but given a choice for me, it's EFI. FTR I love and own new technology.

I hear ya but the problem these days is that most cars that you may want to buy will have one or more of these systems. Then you have to decide if it’s a deal breaker.

 

[demarpaint]

I hear ya but the problem these days is that most cars that you may want to buy will have one or more of these systems. Then you have to decide if it’s a deal breaker.

I hear ya! At the moment if I buy anything new it will be a 3.6L equipped Jeep, so far no still no DI. Hopefully it stays that way. Truth be told nothing else on the market appeals to me or my wife. We had high hopes for the Bronco, lets see if they change the platform in the next year or two, at the moment we're not impressed.

 

[4WD]

I hear ya! At the moment if I buy anything new it will be a 3.6L equipped Jeep, so far no still no DI. Hopefully it stays that way. Truth be told nothing else on the market appeals to me or my wife. We had high hopes for the Bronco, lets see if they change the platform in the next year or two, at the moment we're not impressed.

In 3rd model year FCA played “trading places” with the I4 being base in the Wrangler, a toe in the water ? … now add the Hemi … keep the diesel ? Just wonder if they will stay with that many mills ?

 

[demarpaint]

In 3rd model year FCA played “trading places” with the I4 being base in the Wrangler, a toe in the water ? … now add the Hemi … keep the diesel ? Just wonder if they will stay with that many mills ?

I also wonder about that. I think they covered all bases with the engines. Having said that the turbo 4 doesn't interest me, the diesel was plagued with problems and I wouldn't touch it with a 10' pole. The Hemi would be a little more engine than this old timer needs in a Wrangler. I'm hoping they stick with the 3.6L and continue to improve upon it minus DI, at least until I decide to pull the trigger on another Jeep.

 

[4WD]

I also wonder about that. I think they covered all bases with the engines. Having said that the turbo 4 doesn't interest me, the diesel was plagued with problems and I wouldn't touch it with a 10' pole. The Hemi would be a little more engine than this old timer needs in a Wrangler. I'm hoping they stick with the 3.6L and continue to improve upon it minus DI, at least until I decide to pull the trigger on another Jeep.

I certainly decided it would be my keeper motor … our 2013 was problem free … so did not want to be part of a new learning curve … Good to pick up on the filter housing issue here … same gorillas that jam drain bolts …

 

[WylieCoyote]

My first D.I. engine was in my Mazdaspeed 6. It was the first car I'd ever owned that could soot a completely clean set of exhaust tips on a drive to the grocery store. My commute to work has been 18-19 miles for years, so the oil got hot for a few minutes at least every week day. But the oil still smelled like gas. It's the tradeoff for performance. That engine couldn't have managed 270hp with MPFI. But I scoff at supposed improved MPG. IMO, it's improved performance by way of increased cylinder cooling, and provided a nice side-effect of no fuel condensation in the intake manifold when you crank it to move the vehicle a few feet, and shut it down. I've seen no other advantages.

 

[Cherrybomb]

With these newer engines,and the fuel dilution problem,if you do dealer services to keep warrenty in effect,how do you know if your oil smells like gas?You don't. I recommend oil analysis, thru Polaris. It tells % of gas dilution.If it gets to high on a service,shorten the service.Even if you use the best oil,fuel dilution can be a problem.Addressing it is in your best interest.