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#4577441 - 11/17/17 07:48 PM Premium fuel reducing oil fuel dilution effect?
parshisa Offline


Registered: 05/21/17
Posts: 367
Loc: TX
Does anyone think that running higher octane gasoline can help with fuel dilution? I ran regular all the way through the ownership (around 12k) and last two fill ups I put premium. Checked oil this morning and it looks as if the level is 1/16" below the top mark (where it would stay at all the time) and gasoline odor is gone. So I'm thinking, could this be that whatever gasoline has been introduced to the sump with regular being evaporated now and oil level consequently decreased slightly? I really hate to think the motor has started using oil this early... what are your thoughts fellers?
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#4577459 - 11/17/17 08:02 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
Alex_V Offline


Registered: 04/10/16
Posts: 1117
Loc: Campbellsville, KY
First thought is that premium burns cleaner and the engine can run a little leaner on it, so less fuel to go past the rings in the first place?
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#4577464 - 11/17/17 08:04 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
If you can find Ethanol Free gas that would be my first choice and look in your manual to see what they recommend for octane. Always use this or higher. Especially if you have knock sensor as the change in timing could result in better fuel economy which may lead to reduced dilution.


Edited by StevieC (11/17/17 08:05 PM)
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#4577471 - 11/17/17 08:07 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: Alex_V]
parshisa Offline


Registered: 05/21/17
Posts: 367
Loc: TX
That's exactly what I'm thinking of
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#4577474 - 11/17/17 08:10 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: StevieC]
parshisa Offline


Registered: 05/21/17
Posts: 367
Loc: TX
Manual recommends 87 and higher. actually, fuel economy have improved by around 1mpg which is surprising as my commute has remained unchanged. It might be cooler temps or placebo but the car definitely feels peppier. Don't know. It's just weird that level has changed right after one tank of premium.
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#4577507 - 11/17/17 08:38 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
SilverFusion2010 Offline


Registered: 06/29/11
Posts: 1540
Loc: Crawfordville FL
I don't know that anyone has done scientific testing with this but yes I think premium could reduce fuel dilution.

1. High compression DI engines are set to run rich on 87 to reduce knock, specifically LSPI.
2. If we assume the ECU/PCM is programmed to utilize the knock sensors to control ignition timing, then logically the engine has an idea of the knock resistance of the current fuel.
3. This could be used to set thresholds for safe fuel mix. ECU sees higher octane fuel, and advances ignition timing and leans out the air/fuel mix, resulting in less fuel injected.
4. Less fuel injected means less fuel to leak past the rings and dilute the oil.

I can't say regarding oil consumption. It is possible that the engine has been consuming oil the entire time and fuel was maintaining the level. Now that you have less fuel dilution (theoretically), you're seeing the level drop.
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#4577516 - 11/17/17 08:43 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
Alex_V Offline


Registered: 04/10/16
Posts: 1117
Loc: Campbellsville, KY
IIRC the Cruze detects a change in fuel level in the tank (aka, refueling) and subsequently experiments with timing, etc. to see if it can move to a "hotter" map, so Silverfusion's points are possibly valid.
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#4577523 - 11/17/17 08:50 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
PimTac Online   content


Registered: 03/04/17
Posts: 3484
Loc: Soviet State of Washington
I put Shellís premium in the Mazda last time I filled. Miles per gallon went up about 1mpg or so. I have read a number of threads on other forums that premium does seem to help with fuel dilution. I am too soon into this to know for sure. Car does drive better as if the shift points have improved. All unscientific observations but what I have experienced is telling me to continue on with the 91.
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#4577524 - 11/17/17 08:50 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
supton Offline


Registered: 11/09/08
Posts: 11567
Loc: NH
I don't know about "cleaner burning" but I do like the point about running leaner as it is staying out of knock. I wonder if a Scanguage or Torq connection would indicate how much timing is being used (or pulled), on 87 vs 93, and if that would be a decent "test" of knocking.

I have to wonder: has anyone bothered to calculate the cost savings of the mpg bump from using premium (if any) vs the cost of a shortened OCI + savings using lower octane gasoline?
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#4577585 - 11/17/17 09:46 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
Danh Offline


Registered: 10/16/10
Posts: 1710
Loc: .
Same experience with my 2015 DI CRV: Interstate driving into a strong headwind would typically increase the crankcase level on 87/89 octane fuel. 91/93 prevents this. Oddly, with 93 octane fuel in the same conditions I saw an actual reduction in crankcase level of about...1/16 inch. First time ever.

My speculation is that Honda uses fuel enrichment and/or injection timing in addition to or instead of retarding ignition timing when spark knock is detected. And with ultra-high gearing current Hondas may verge on spark knock a lot of the time.

So I'm a premium fuel convert even though the manual only calls for 87 or higher. On one hand I'm irritated that Honda runs this close to the edge and kind-of lies to its customers. On the other I'm happy there's at least a partial solution.

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#4577596 - 11/17/17 10:04 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
SilverFusion2010 Offline


Registered: 06/29/11
Posts: 1540
Loc: Crawfordville FL
E85 seems like it would solve a lot of these issues. Lots of political attatched to e85 though.

From a purely mechanical and chemical view, its high octane, plus high heat of vaporization (charge cooling) make it an excellent match for high compression and direct injection.
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#4577623 - 11/17/17 10:51 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
anndel Offline


Registered: 05/28/09
Posts: 245
Loc: Hawaii, USA
All of our 2 trucks and car specs 87 octane per the owner's manual. We run premium gas in the car and 93 Yota truck which gets better gas mileage and more response. The '14 Tacoma still runs regular but I've been filling with premium when I can. Of course the tree huggers say otherwise and to only use regular.

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#4577632 - 11/17/17 11:25 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: SilverFusion2010]
Colt45ws Offline


Registered: 08/15/06
Posts: 9612
Loc: Central Washington
Originally Posted By: SilverFusion2010
I don't know that anyone has done scientific testing with this but yes I think premium could reduce fuel dilution.

1. High compression DI engines are set to run rich on 87 to reduce knock, specifically LSPI.
2. If we assume the ECU/PCM is programmed to utilize the knock sensors to control ignition timing, then logically the engine has an idea of the knock resistance of the current fuel.
3. This could be used to set thresholds for safe fuel mix. ECU sees higher octane fuel, and advances ignition timing and leans out the air/fuel mix, resulting in less fuel injected.
4. Less fuel injected means less fuel to leak past the rings and dilute the oil.

I can't say regarding oil consumption. It is possible that the engine has been consuming oil the entire time and fuel was maintaining the level. Now that you have less fuel dilution (theoretically), you're seeing the level drop.

Yes, I believe this to be the most likely. Most OEMs are probably playing with the timing and fueling constantly to get the most efficiency from these engines, running right on the knock threshold.
High compressio, Forced induction DI engines are likely running rich on 87 in order to combat knock. It makes sense to me then that feeding it high octane may well prevent fuel dilution.
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#4577637 - 11/17/17 11:36 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: SilverFusion2010]
Colt45ws Offline


Registered: 08/15/06
Posts: 9612
Loc: Central Washington
Originally Posted By: SilverFusion2010
E85 seems like it would solve a lot of these issues. Lots of political attatched to e85 though.

From a purely mechanical and chemical view, its high octane, plus high heat of vaporization (charge cooling) make it an excellent match for high compression and direct injection.

A few years ago Ford built a test ecoboost with both DI and port fuel. DI was E85 and port was 87. They ran 87 primarily and shifted onto the E85 under higher load. It made something like 800ftlbs gross. The idea wouldve been two tanks, a small one you fill with E85 and the other with regular.
Obviously I dont think they persued it for lack of infrastructure (Ive never seen E85 in my state) and Im sure people would mix them up regularly. Which isnt really a problem, Im sure they wouldve figured out a limp mode when running just 87 or if someone filled the DI tank with 87 but still would cause a huge performance drop.
But it shows what you could do if say you wanted to run one on just E85 and retune the computer to get max power. That 800ftlbs gross would probably turn into 600-700 at the wheels. Thats unreal from a gas V6.


Edited by Colt45ws (11/17/17 11:36 PM)

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#4577641 - 11/17/17 11:48 PM Re: Premium fuel reducing oil fuel dilution effect? [Re: parshisa]
Bryanccfshr Offline


Registered: 10/09/04
Posts: 5665
Loc: Durango, Co
Fuel quality.
Itís makes a difference.
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