4 gas-saving 'tips' that don't work

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Advice such as buying gasoline in the cool of the morning or leaving the tailgate down has been tried -- with disappointing results. 

There are a lot of smart ways to save on gas. For instance, you can use a website such as GasBuddy to find cheaper gas stations in your area, buy a more fuel-efficient vehicle or drive less aggressively so your car uses less gas. 

These are all proven methods for reducing how much you need to budget for gas, but there are other widely used methods that don't pass the smell test. Here are a few. 

Buy gas early in the morning.

Gasoline is denser at colder temperatures, so the theory here is that if you fill up early in the morning while it's still cool out, you'll get more bang for your buck -- a gallon of gas bought cold will expand to be a little more than a gallon when it gets warmer. Gas at gas stations is stored in underground tanks, where the temperature varies a lot less than it does on the surface. As such, there's going to be little to no perceptible difference in the density of the gasoline whether you buy it in the morning or at night. 

With that said, it still might be worth it to fill up in the morning because, given how quickly gas prices have been rising, you might find that the price has gone up by a few cents by the time you get back to the station that evening.

Over inflate your tires. 

Yes, it's true under inflated tires lead to decreased mileage, so you should make sure your tires are properly inflated for fuel efficiency and safety reasons. But some people have taken that to the logical extreme by inflating their tires beyond the recommended pressure, the theory being that an overinflated tire will have a smaller contact patch with the pavement and thus less resistance. Alas, it turns out that's not really the case: Popular Mechanics tested this one out and found almost no difference in gas mileage between 32 psi inflation and 45 psi. 

Turn off the air conditioning and lower the windows. 

The theory here is that air conditioning draws energy from the engine, and that lowering the windows reduces drag. Thus, on a warm day you should turn off the air conditioning and lower the windows to boost your gas mileage. Unfortunately, there appears to be little truth to this method: Edmunds tested it back in 2005 and found that the mileage was the same no matter which method they used to cool themselves. If it's hot out, don't hesitate to blast the A/C. 

Leave your tailgate down. 

Many pickup truck drivers will leave the tailgate down, the idea being that having it up will "catch" the air flowing over the truck, acting as a sail that increases drag and makes you burn more gas. But the Discovery Channel's hit show "MythBusters" tested this one and then retested it and found that fuel efficiency was actually a little better with the tailgate up. That's right, keeping your tailgate open actually made things worse, and putting a cover on the pickup truck's bed had no real impact on fuel efficiency.