Give mine a good reason why I should...

[ammolab]

I have to wonder how higher octane can make a car IDLE smoother??

The octane requirements at that speed/throttle opening/cylinder pressure must be REALLY LOW!

Placebo effect (there someone DID mention it!)

I ran my 2000 Audi S4 Twin turbo V6 on 86/87 octane on LONG interstate trips..crusing at 80mph with 14mm Hg of vacuum in the intake manifold (no need for boost)..I never noticed any loss of MPG or smoothness or idle degrade. I just filled up with 93 octane at my destination.

 

[tommygunn]

Originally Posted By: ltslimjim
The old Civic's manual specifies 86 octane.
probably to take into the difference of Colorado and such that have lower octanes.

 

[urchin]

Any car ECU from the past 15 years or so should have NO problem adjusting the spark, timing, ect for any typically offered gas grades in the USA.

Anything from 85-93.

Unless the manual specifically states to use only 93.

You can use any octane without any problems or noticable decrease in performance.

 

[mechtech2]

If you are getting the massive 3-5 MPG increases, then the cars NED that higher octane. I would continue using it for sure.
Knock sensors go of easily, and pull LOTS of advance, Hence, the lousy power and fuel economy.

 

[Jimmy9190]

I finally had to buy gas again today. I filled up with Shell regular 87 octane. After I got home I checked my MPG on fuelly.com and it went down about 1 MPG. I am sticking with 87 for now anyway. My truck didn't really run any better on 89, but it didn't run any worse either. For the extra cost I don't think the mid grade gas was worth it.

I may do some more tests with mid-grade later on. I don't drive as much now that I work from home so it's kind of a wash even if I were to somehow gain a little MPG on mid-grade gas.

 

[MikeLW79]

Gasoline is a "witches brew" so to speak. It has way too many variations from brand to brand. Your car is programmed to run a slew of different octanes from 87- 93 at minimum. The computer controls ignition timing to compensate pre ignition anyway. Run what you want and drive. Dropping a MPG here or gaining an MPG there is as simple as the barometric pressure fluctuating, your lead foot being demanding, or mechanical/chemical changes in the fuel itself or your car.