Fuel Dilution & UOA's?

[buster]

Question, it's been proven recently that running premium fuel in the Skyactiv Mazda DI engines eliminates the fuel dilution issue. Would this apply to other engine familes as well? I'm sending off my sample of M1 0w20 with 8k miles on it from the Mazda. I've used nothing but premium fuel other than maybe 2x i accidently put regular in it.

Could it be a fuel issue that is causing this?

 

[Quattro Pete]

What is it about premium fuel that helps eliminate fuel dilution? Just curious...

 

[buster]

I'm not sure QP, I've been wondering that as well. It does seem to work per the UOA's I've seen so far. badtlc and Artem both told me about it and the UOA's do seem to show that running premium in the Skyactiv engine reduced the fuel dilution. I'm not sure what the mechanism is driving it.

 

[440Magnum]

Until I hear a reasonable explanation with some repeatable data, I consider the effect of premium fuel on dilution to be a myth.

The only POSSIBLE explanation I could imagine is that the knock sensor is triggering some enrichment, but then fuel economy would take a clear hit on regular fuel. I don't read reports of Skyactive DI engines getting significantly better mileage on premium. Color me skeptical.

 

[ccap41]

Just an idea but doesn't higher octane fuel burn faster? If it burns just slightly quicker than getting mixed in then that could be a problem solver.. but that is just an idea.

Also, everybody mentions premium or 91+ octane. Does anybody use 89? mid grade?

 

[Koz1]

Its a high compression engine so fuel quality would make a huge difference, as long as you use a high quality fuel 100% of the time it should be good.
Does anyone have information where the high fuel UOAs are taking place, is it more concentrated in a region of the US and or Canada?

Temperature of the charge plays a big part in Mazdas skyactive engines so city crawl will cause fuel dilution as knock will occur much more often with reg gas as temps rise under the hood premium fuel will be better suited to stop abnormal combustion in the cylinders as that's what its designed for.

Maybe an air evacuation system should be employed on the new SA engine compartments, even more air flow through the engine compartment keeping things cooler.

 

[Quattro Pete]

Originally Posted By: ccap41
Just an idea but doesn't higher octane fuel burn faster?

No it doesn't. Higher octane just means the fuel is less prone to auto-ignition.

 

[OneEyeJack]

Higher octane gas burns slower.

 

[John_Conrad]

Higher octane fuels burn slower and cooler, that's why they're used in high compression engines.

However, throw in the ethanol mandate convoluted mess on a per state basis(where most the time you don't know what you are putting in) and testing becomes a real challenge....especially if you are traveling around several states or on a long trip.

 

[Koz1]

Better cooling of the head, does the SA engine flow through the head for block first?

 

[ccap41]

Originally Posted By: John_Conrad
Higher octane fuels burn slower and cooler, that's why they're used in high compression engines.

However, throw in the ethanol mandate convoluted mess on a per state basis(where most the time you don't know what you are putting in) and testing becomes a real challenge....especially if you are traveling around several states or on a long trip.


Thanks, I obviously had it backwards..

I knew it burned cooler but I thought it was faster. My bad.
..there goes that theory..

 

[wemay]

I would need to see more data than a few UOA. Not saying it isn't true, just cannot rely on UOA for this.

 

[Quattro Pete]

Originally Posted By: wemay
I would need to see more data than a few UOA. Not saying it isn't true, just cannot rely on UOA for this.

Totally agree with this. Just the conditions under which the sample was taken will affect this greatly. Not to mention the fact that some labs (ex. Blackstone) don't actually measure fuel dilution. Instead, they guesstimate it off flash point.

 

[buster]

^ True.

 

[Eddie]

Several UOA data points is not significant enough to make any meaningful statement. I think this is a test to be performed by a lab under controlled conditions. The valves carbon/crud might measured before and after a 50,000-100,000 mile test program. Ed

 

[bluesubie]

Premium fuel definitely has had no impact on the fuel dilution seen in the the new Subaru DIT engine in the WRX and Forester. I would presume that all of those owner's are running premium since it's required/recommended.

Lots of WRX guys are also switching to OAI for their fuel testing. They're also switching to ACEA C3 5W30's since the low 20 grade viscosity and low flashpoint seen in GF5 5W30 UOA scares them a little.

UOA's on cars with long warm-ups during winter were the worst.

-Dennis