Friday, April 29, 2011

Save $$$ at the Pump

As gas approaches $4 per gallon, we are all looking for ways to save. Lots of advice is circulating around, but which tips will actually save fuel? Let’s separate fact from fiction:

Fact: Slow down.

Why? There’s this little problem of air and drag. As you zoom down the road at high speeds, your car pushes lots of air ahead of it and leaves a “hole” in the air behind it. The difference in air pressure creates suction that tries to pull your car backwards. At highway speeds, your car uses about 40% of its energy to push the air around, so try to leave your lead foot at home.

Fiction: Pump your gas in the morning.

Why not? The theory behind this myth: cooler temperatures make the fuel denser so you pump more gas molecules in every gallon. However, gas is stored in an underground tank whose temperature varies very little throughout the day, so the temperature of the air really has little effect on the temperature and density of the fuel.

Fact: Keep your tires inflated.

Why? Underinflated tires mean more tire surface on the road, thus more friction. Keeping your tires inflated will not make a huge difference in your fuel costs, but every little bit helps, right?

Fiction: Change your air filter.

Why not? You should replace your air filter regularly, but not because it will save money at the pump. The computer sensors in modern cars adjust the fuel-air mixture continually. A dirty air filter will not cause your car to burn more gas, but it will decrease your engine power. In other words, your car will be somewhat sluggish, sort of like you might feel on Monday morning.

Fact: Jack rabbit starts waste gas.

Why? Think about it; your car probably weighs about 2 tons. The amount of energy to accelerate 2 tons from a stop is considerable, so city traffic will cost you a lot of fuel. Take it easy on starts and stops; in other words, don’t drive like a maniac. Your savings could be as much as 30%!

Fiction: Use premium fuel.

Why not? Let’s say you recently bought the sports car you always wanted, and the owner’s manual says “premium fuel recommended.” Uh-oh, premium fuel is expensive! Will you get better gas mileage with premium? Will you harm your engine with regular? The answer is probably “no” to both. Your gas mileage probably will not be affected, and your engine sensors should detect the lower octane and adjust the timing. However, if your new car says “premium fuel required”, you had better fork over the extra for premium gas.

Fact/Fiction: Turn off your air conditioner.

OK, I am being wishy-washy. The answer here depends on your speed. In the city, running the A/C will cost you more, but on the highway, running the A/C will actually save fuel. There is no question that the A/C uses a lot of your engine’s power, so turning it off whenever you can is a good idea. However, open windows create drag which increases the faster you go. So opening the windows at highway speeds will create enough drag to cancel out the savings. Generally, at speeds over 45 mph, you can justify using the A/C. As you might imagine, windows closed with the A/C off is the best option, but that would be a mite unpleasant on a hot August afternoon.

Happy driving!

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