Do you have a gas saving tip that actually works?

With gasoline prices hitting record levels, it seems everyone has a tip on how to save fuel. Much of the advice is well-intentioned, but in the end, much of it won't lower your gas bill. Here's a look at a few misconceptions floating around the internet:

1. Fill your tank in the morning - You may have heard that it's best to fill your gas tank in the early morning while the fuel is cold. The theory goes that fluids are more dense at lower temperatures, so a gallon of cold gas actually has more gas molecules than a gallon of warmer gas. But the temperature of the gasoline as it comes out of the nozzle varies little during the course of the day, according to Consumer Reports.
2. Change your air filter - Maintaining your car is important, but a clean air filter isn't going to save you any gas. Modern engines have computer sensors that automatically adjust the fuel-air mixture as an increasingly clogged air filter chokes off the engine's air supply.
3. Use premium fuel - With prices already over $4.00 a gallon, premium gasoline is a hard sell these days. But a lot of drivers think because their owners' manual recommends premium, they'll get better fuel economy with it. Really, they may be paying more money for nothing. Newer cars for which premium is "recommended" - but not "required" - won't suffer with regular fuel.
4. Pump up your tires - Proper tire inflation is important for a number of reasons. Under-inflated tires are bad for handling and can even cause a crash. Improper tire inflation also causes tires to wear out faster and to heat up more, which could trigger a dangerous high-speed blow-out. According to on-the-road driving tests by both Consumer Reports and auto information site Edmunds.com, underinflated tires reduce fuel economy, so proper inflation is key. But you should never over-inflate your tires. They'll get you slightly better fuel economy because there will be less tread touching the road, reducing friction. But that means less grip for braking and turning. The added risk of a crash isn't worth the extra mile a gallon you might gain.
5. To A/C or not A/C - There's no question air-conditioning makes extra work for the engine, increasing fuel use. But car air conditioners are much more efficient today than they used to be. In around-town driving, using the A/C will drop fuel economy by about a mile a gallon. Meanwhile, driving at higher speeds with the windows down greatly increases aerodynamic drag.
6. Bolt-ons and pour-ins. Before you buy a device that's supposed to make your car more fuel-efficient or pour in an allegedly gas-saving additive, ask yourself this: Don't you think oil and car companies aren't doing everything they can to beat their competitors? There are a number of these gas-saving devices that are generally useless.