Fuel Octane Question/Observation

[jhrain]

We are in Iowa this week. The SHELL gas station, for whatever reason, was out of regular and mid octane fuel.'

So, I put in premium. Our gas mileage jumped almost 2mpg. We're not driving any differently than before. Just filled up with a third tank and it too was up by exactly 2.1mpg.

Is it possible that this engine can sense and take advantage of higher octane fuel?

I'm not looking for people to speculate. I've seen other posts here were people were "speculating" about fuel & octane levels.

We have a new SL AWD model with a little more than 1100 miles on the odo. I know some engines can sense and take advantage of higher octane levels, but it's not commonly referenced in any manuals.

JIM

[xsvhp]

Your ECU is probably allowing the timing to be advanced because it is not sensing detonation. In some cases, this slight advance in ignition timing is conducive to better mpg AND power.

Pretty rare, but I've seen it happen on some cars which are set at the factory to allow as much timing advance as possible.

[Phil'sFrontier]

There are so many variables that effect gas mileage. Maybe you were going slightly downhill. Or downwind. I can't see higher octane fuel giving you that much better mileage, otherwise wouldn't it be recommended.

[philipa_240sx]

Your ECU is probably allowing the timing to be advanced because it is not sensing detonation. In some cases, this slight advance in ignition timing is conducive to better mpg AND power.

Pretty rare, but I've seen it happen on some cars which are set at the factory to allow as much timing advance as possible.

The B15 Sentra SE-R has a similar QR25DE motor to the Rogue and was quite sensitive to engine knock/detonation. It would pull timing on a whim it seems. That motor also had a fairly aggressive timing curve unlike the same QR25DE motor used in the Altima. I tried regular and premium fuel in my '03 Alty with the QR. I never got any better fuel economy. I expect the Rogue to be the same in this regard although I have not tried it.

I think jhrain's increase in fuel economy is more attributed to other factors:

- driving habits- the engine is breaking in. I saw a stready increase in fuel economy after the first tank in fuel. I went from 22 mpg when new to 28 with over 7000mi on the odo.

[websfear]

Not sure if it country wide, but here Shell premium is 100% gasoline, where the other grades are 10% Ethenol. That could increase your gas mileage.

[jhrain]

My driving habits have so far been the same... and in Iowa SHELL gasoline is formulated with 10% Ethanol (supporting the corn industry)... but, I did learn that BTME is no longer included in their fuel.

I also concur that the engine could simply be breaking in and hopefully mileage will continue to improve.

I'm back in Missouri tomorrow. BTME is still included in the fuel there, at least for a little while longer... I wish I could find pure gasoline in Saint Louis. Everyone here is also forced to use a fuel with added ethanol.

Cheers,JIM