So the Challenger can run on either 87 or 89 octane unleaded fuel and today I put about a quarter tank in it to see how far it would take me. Mixed mpg is rated at 20, but what I discovered was far more startling.

The Chally only made that quarter tank last 30 miles using the Eco light in the trip odometer.

A bit disappointed, I spent $50 bucks on a full tank of 89 octane gas and that just about tripled my mileage. After driving 40 miles the gauge hasn't really moved. The extra 11 cents per gallon (87 is $3.79 and 89 was only $3.90) might be worth it.

But what I think is interesting is that I can remember 87 octane being of a much better quality than it is now, even at higher prices. The more I think about it, the more I think what's being sold as 87 octane just, well, isn't.

Your thoughts?

The only thing I've noticed so far with the Legacy requiring 91 or higher... The prices don't fluctuate as much as the lower octanes do. Otherwise, I have no plans of using a lower grade since its required.

I would try again later on a tank of 87 from another station... that one may be iffy in a way not related to octane, such as water in the fuel.

I've noticed better readings with 89 myself with the Cobalt.....very interesting...

My S-Series runs fine on 85. lol (high elevation apparently makes 85 roughly equivalent to 87)

My S-Series runs fine on 85. lol (high elevation apparently makes 85 roughly equivalent to 87)

It does because there is less air... so the air/fuel mix is less likely to preignite.

I tend to go with what the manufacturer recommends, cars tend to run like $h! on lower than recommended octane fuel.

I tend to go with what the manufacturer recommends, cars tend to run like $h! on lower than recommended octane fuel.

When you go up in the mountains, you can't always get the octane rating you expect. 85 octane at high altitude would test like 87 _IF_ the test was done at high altitudes... but since the tests are done for sea level, and there are laws about octane ratings, they have to sell it as 85, even at high altitude. This was covered recently as a question in one of the auto mags.

Remember, the octane rating on gas has nothing to do with octane the chemical... and the rating changes with altitude.

In BK's example, the acceptable octane rating for the Challenger is 87. I still think he got bad gas, as the mileage was SO far off.

Being a 3.5 owner I recommend using at least 89 mid grade. I have never gone lower than 89 as long as I've had it.

it's not the gas, it's the car. some engines just don't do well on low octane.