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87 octane vs 93

Bought a 2008 Equinox in Sept 2010 with 14500 miles . It normally uses 87 octane but I’ve always used 93 whenever we take long trips on the interstates, we normally get around 20 mpg city and 23 hgwwith 87 with 93 it goes to 29 hgw. The wife says we’re going to ruin the engine by using the 93. Who’s right and does it make $$ sense to use 93. She drives 12 mile a day to nad from work and most weekend trips are short trips.

You won’t damage the engine using 93 octane gas. But, I’m very skeptical that 93 boost the highway miles more than using 87.

If you use 87 on the interstates you should get the same mpg or even better than using 93 in a car designed and tuned for regular gas. I think you are experiencing a placebo effect.

Other factors (weather, route, traffic) is more likely to be the reason for the 2 MPG increase when using 93 octane. The engine in your car is designed to run on 87 octane, there is no benefit to using premium in this car. But you aren’t going to ruin it by using premium either.

Your wife is right about not using 93 but for the wrong reason. It’s cheaper and fine to use 87.

The OP is claiming a 6 MPG increase, not a 2 MPG increase. That seems extremely unlikely to me.

The different fuel will make very little or no difference in your mileage.

Octane is not a measure of quality or power of the fuel. It is a measure of how fast the fuel burns. High octane burns slower which is what a high compression engine needs.

I suspect there was other reasons for the difference in reported mileage for the two different octane fuels.  

How was the mileage measured?  Are you using an on board computer to measure the mileage?  If so I suspect the difference is due to an error factor in measuring the mileage.  Those computers are not all that accurate and tend to favor one driving style over another for reasons other than real mileage differences.

If you want to really know, you will need to run two or three full tanks of fuel for highway with high octane city driving, and then two or three with regular octane.  Then repeat with high octane.  Or you can just take our our word for it.  

Just for fun do several fill ups with regular and measure using pen and paper total miles divided by the number of gallons consumed.

Oops, I misread the original post. You’re right gaining 6 MPG simply by using 93 octane in a car that only recommends 87 octane anyway, is quite unlikely.

Does this engine have a knock sensor?

It’s possible that some issue like carbon build up or a clogged EGR passage is causing the engine to start knocking with 87 octane.
Then the knock sensor picks this up and causes the engine computer to retard the timing, which can reduce the MPG.

We used the cars onboard computer to get the mpg avg, we ran approx. 280 miles of interstate driving and the rest city. Don’t remember total miles driven but remembered that we did use 93 without ethanol

My wife is always chiding me that she gets better mileage on our 4Runner than I do. Once, on a trip, I accidentally put in a higher octane gasoline. The owner’s manual says that 87 octane is o.k., but one might get better mileage and performance with a higher octane. I thought maybe my mileage would improve and I would have some bragging rights. However, the mileage was lower with the higher octane gasoline. It may have been due to the fact that the wind picked up. At any rate, I put in 14 gallons and paid ten cents more a gallon, so putting in the higher fuel cost me $1.40 with no gain in mileage.

All cars get better mileage on the highway than they do in the city…It’s the type of driving, not the octane, that is improving your mileage…

93 octane will not boost the fuel economy. It also will not damage the truck. It will damage your wallet, though. You may think that you get better mileage, even if you have driven the same route using both regular and premium gasolines. But you can’t drive the exact same route exactly the same way. Save money and buy regular gas. Take the wife out to dinner with the money you save.