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Car Corner
Gas Mileage Revisited

July 1, 2002
By Scott Lewis

This month I want to take a look at a couple of items. They come under the umbrella of gas mileage. I have spent some time trying to determine if the quality of gas really does effect mileage. I have also read some interesting news about hybrid vehicles. I thought it was time to tackle these issues again.

Gas Quality vs. Gas Mileage

I once wrote about the mileage I was getting and how driving style and quality of gas seemed to have a significant effect on overall mileage. I tested different driving techniques to see how they faired at the pumps. I accidentally discovered I got better mileage with premium grade gasoline.

I decided to look at the quality of gas a little more deeply. Having settle on a driving style that is consistent, I thought I would take a look at how the quality of gas really effects mileage over the long haul.

I ran three tanks of premium (93 Octane) gas in my car and recorded the mileage and gas used each time. Then I ran one tank of the middle grade (89 Octane) gas through my car to insure there would be no remnants of the good stuff. I then ran three more tanks of the 89 octane gas recording my mileage.

I combines the three tanks for each grade of gas and determined the mileage. Here are the results:

Gas Miles Gallons Mileage Price Cost MPD*
93 874.5 43.796 19.97 $1.499 $65.65 13.32
89 732.1 37.957 19.28 $1.399 $53.10 13.79

MPD is miles per dollar. This is the key here. Notice that I did get better miles per gallon with the high octane gas, but overall cost... mile per dollar... was lower with the lower grade gasoline. 

Conclusion

Although my car get slightly better gas mileage with premium fuel, it is more cost effective to run the lower quality. Since my car doesn't get knock or ping on 89 octane gas then that's good enough for now.

Hybrids

Honda recently released a hybrid version of the Civic. This car uses the same technology as the Honda Insight, but in a car that we can use for direct comparison with, namely the standard gasoline powered Civic. Honda's hybrid engine system (though flawed in my opinion) works by using the electric motor to help the gasoline engine by providing extra power when needed. This allows the gasoline engine to be smaller, hence getting better gas mileage.

Mileage... At What Cost

The Civic Hybrid gets 51 mpg on the highway. A Civic EX is rated at 38 mpg highway. The hybrid Civic costs approximately $1500 more than the gasoline only car.

Time for some math:

Car Mileage Price Total miles Cost
Gas Only 38 $1.39 50,000 $1828.95
Hybrid 51 $1.39 50,000 $1362.75

That's a savings of $466.20 over 50,000 miles. The simple math would take that to $932.40 for 100,000 miles. How long would you expect to keep a car. Even if you did keep it for 100,000 miles you still didn't save enough money on your gas bill to justify the upfront cost of the hybrid vehicle. And this is made worse if you take into account that you will be paying interest on that $1,500 with your car payments. It gets even worse if you go in reverse... assume you banked the $1500 you saved getting the gas only car, it would earn interest for you, making the difference even more.

I have said this before... it is costly to decide to start getting good mileage. Most "upgrades" to get good mileage cost far more than the benefit they provide at the pump.

As for the Civic, I would not want to own it at the 100,000 miles. That's when the battery packs need to be replaces at a cost expected to be about $2,000. Ouch! Another reason to try my plan for a hybrid.

Conclusion

Don't bother paying extra for high mileage unless you have an uncontrollable urge to be environmentally friendly or on the bleeding edge. It just doesn't pay... yet.

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