I can't quite wrap my head around GDI engines and fuel dilution of the engine oil

When I look at used engine oil reports that folks post from their GDI vehicles, it's evident that fuel dilution continues to increase with mileage. And that's one of the main reasons it's recommended that GDI owners change oil by about 5K miles or so, regardless of what the owner's manual or engine's oil change indicator says.

I guess it doesn't make sense to me that just a single hour of highway driving wouldn't cook all the gasoline out of the engine oil, reducing the dilution amount to zero each time you made that one hour highway trip. Heck... gasoline has a flash point of something like -45˚ F. But it somehow manages to stay in the oil. Interesting...

Gasoline is a cocktail of various chemicals, some of which have boiling points of 250-450 degrees F. Your oil doesn't get hot enough to fully remove all of these chemicals.
 
Many of the modern GDI engines come with higher compression. My Mazda has 13:1.

Also, the fuel injectors do not just inject at TDC. The computer tells them when to inject fuel and in some cases they inject multiple times during a cycle. When the engine is cold they run very rich in Order to expedite warm up and for the catalysts. That’s how cars that run short trips and especially in colder weather can develop fuel dilution.

GDI has been around for quite some time. Mitsubishi was putting them in vehicles thirty years ago at least.
Moving to the country and increasing the minimum trip distance stopped my wife's Sonata from making the oil smell like gas within 2k miles. It always smelled very gassy when she drove 7 minutes to work each day.
 
Some of it will but not all of it. Plus the presence of the fuel can cause permanent degradation of the viscosity index improvers used in the oil. Gasoline in the oil is not as benign as people like to believe.
Can cause. Again, where are the failures?
 
Can cause. Again, where are the failures?
I might guess That data is held close to the vest and isnt' available to the public unless there is a class action.

As I was breaking in my '20 Cleveland Ford/Mazda 2.0L D.I. with 12:1 compression. Started getting the engine rattles after 1.5- 2K miles on an oil change
Wasn't sure what was going on . The O.M. was stating that if you notice engine noise you may require a higher octane fuel. Tried that. Problem persisted, Then after a 100 mile highway round trip the engine was running hot underhood. Couldn't touch anything. Temp gauge reading was normal. Pulled up the dip stick - I had stopped for fuel - oil was just touching the bottom tip. Went the 10 miles home as is. let it sit. Oil was down over a quart and a half.
Oil level checked as good just the previous week.

Now the engine makes a lot of racket like over-clearanced rod bearings. It knocks on transition to off throttle when you unload it.
Yes this could be a cam phaser issue but it presents as classic rod knock. 10W30 helps it quite bit but once the oil gets hot the issue persists.

Oil appearance (5 drops) on a paper tissue at 2k miles in service. Calculated 2.5% fuel dilution on UOA

20220321_133158.jpg
 
Low tension rings and short tripping allow unburnt fuel to get into the crankcase and accumulate. The fuel will burn off once the vehicle reaches operating temperature. The amount of fuel dilution is engine dependent. Some TGDI engines experiences this and some do not but people love to paint with a broad brush.


Note: To those who want to chime in and say that a TGDI won't last 350k miles. The reality is that nobody cares, seriously, nobody cares. Go scream at the neighbors dog or something.
BMW uses low tension rings and doesn't have the fuel dilution problems seen with marques like Honda, so I wouldn't be inclined to consider that a significant factor. I think there are other design issues in play as well as the software.
 
BMW uses low tension rings and doesn't have the fuel dilution problems seen with marques like Honda, so I wouldn't be inclined to consider that a significant factor. I think there are other design issues in play as well as the software.
That may be due to BMW engines running HOT! My B58 6 banger keeps the oil at ~220F just puttering around town.
 
Hyundai/kia products and German vehicles. Not all models are susceptible to it but both use primarily DI and both have the worst reliability records as far as engines go.
Huh? BMW, VW have been doing DI for almost 20 yrs. Mercedes a little less. Again where are the failures from fuel dilution?

Hyundai/Kia have problems in general. Some of which are user error (ie. Delayed oil changes) and manufacturing flaws.
 
I might guess That data is held close to the vest and isnt' available to the public unless there is a class action.

As I was breaking in my '20 Cleveland Ford/Mazda 2.0L D.I. with 12:1 compression. Started getting the engine rattles after 1.5- 2K miles on an oil change
Wasn't sure what was going on . The O.M. was stating that if you notice engine noise you may require a higher octane fuel. Tried that. Problem persisted, Then after a 100 mile highway round trip the engine was running hot underhood. Couldn't touch anything. Temp gauge reading was normal. Pulled up the dip stick - I had stopped for fuel - oil was just touching the bottom tip. Went the 10 miles home as is. let it sit. Oil was down over a quart and a half.
Oil level checked as good just the previous week.

Now the engine makes a lot of racket like over-clearanced rod bearings. It knocks on transition to off throttle when you unload it.
Yes this could be a cam phaser issue but it presents as classic rod knock. 10W30 helps it quite bit but once the oil gets hot the issue persists.

Oil appearance (5 drops) on a paper tissue at 2k miles in service. Calculated 2.5% fuel dilution on UOA

View attachment 134255
So your oil level was down over a quart and you're attributing that to fuel dilution?
 
Let’s not forget that gasoline has lighter and heavier components as well as being a petroleum product, it will fully mix with oil. The lighter components may evaporate but the heavier ones will stay mixed with oil and may never be flashed off, IMO.

I don’t think it’s as simple as getting the oil hot for long enough to get rid of gas contamination. Some will always be there, hence changing the oil early is probably the best if one suspects elevated gas contamination, like actually smelling gasoline in oil.
 
It takes me 20 miles on the highway before I reach 180F on the oil temp. Short trippers own a nightmare if GDI only. I don't know at what temp the evap rate is higher than the refill rate. I don't know how long it will take for the evap rate to overcome previous dilution filling. Obviously, the automaker wasn't prepared for the US consumer.

Looks like the R&D was a complete failure. Informed consumers eventually figured out what was happening.

Modern manufacturing! Trust your automaker! Trust your dealer! I've heard all the cliches on too many forums with too many brands/models... their pitiful clueless blind trust existence!

I also know that some cam driven HPFP's leak. They might be dripping into the oil. Scary thought. Quality control or expectations of the HPFP might also be excessive.

lol. DI makes so much more power and efficiency it is not even comparable.
 
When I look at used engine oil reports that folks post from their GDI vehicles, it's evident that fuel dilution continues to increase with mileage. And that's one of the main reasons it's recommended that GDI owners change oil by about 5K miles or so, regardless of what the owner's manual or engine's oil change indicator says.

I guess it doesn't make sense to me that just a single hour of highway driving wouldn't cook all the gasoline out of the engine oil, reducing the dilution amount to zero each time you made that one hour highway trip. Heck... gasoline has a flash point of something like -45˚ F. But it somehow manages to stay in the oil. Interesting...
What was the ambient temp during your drive?
 
I guess the engine makes a pour refinery at separating the oil and fuel, once they are mixed together in harmony and synergy.

I have a feeling that the amount of fuel might be excessive. I don't want to believe the automakers didn't notice this with their GDI tuning. They also didn't notice LSPI, IVD.... and the list goes on.

The question you should ask... HOW MANY GALLONS OF FUEL MAKES IT INTO THE OIL SO THAT THE UOA shows that 5-10 ounces not evap'd at any given point? and would you notice it?

My wife drives 4000 miles and uses 200 gallons of fuel. Would I notice if it was really 199 gallons or 201 gallons? I won't guess at the accumulation or evaporation rate. How many gallons of fuel do you think you're oil and PCV are processing continuously? Then, be scared. Gallons might be blown past your rings over your 10k or OLM interval.
 
Not naturally aspirated it doesn't.
The 6.2L ECOTEC3, which is DI, is 420HP; 67.74HP/L
The 5.7L HEMI, which is PI, is 395HP; 69.3HP/L

The big advantage of DI is with forced induction.

That's mostly true, but there are still nice gains NA. Many NA engines have switched to DI and it's not because it's cheaper and easier. Your example is a bit odd using two completely different engines.
 
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