Debunking gas-saving tips

With average gas prices in Greater Boston in April topping the prices of the energy crisis of the early 1980s, and AAA now expecting the first decline in Memorial Day travel since 2002, our friends at CNNMoney.com asked the folks at Consumer Reports to take a look at a half dozen pretty widely circulated myths and debunk them.
Ever hear that running your air-conditioning wastes loads of gas? Or that a dirty air filter really hurts mileage. Apparently, not true.
Here's what they found:

No. 1: Fill your tank in the morning
The theory goes that fluids are more dense at lower temperatures, so a gallon of cold gas 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, offering little, if any, benefit.

No. 2: Change your air filter
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. While engine power will decrease slightly as the air filter becomes clogged, any increase in fuel consumption will be negligible.
No. 3: Use premium fuel
Even cars for which premium is recommended won't suffer with regular fuel. When sensors detect regular instead of premium fuel, modern auto systems automatically adjust spark plug timing. The result is a tiny reduction in peak horsepower but no reduction in fuel economy.
No. 4:. Pump up your tires

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. 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, increasing your risk of a crash.

No. 5: Gas-sucking AC

There's no question air-conditioning makes extra work for the engine, increasing fuel use. But ACs 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.
Ironically, many drivers, trying to keep the AC off, opt instead to drive at higher speeds with the windows down, increasing aerodynamic drag. As speed increases, drag becomes more of an issue, making A/C use the more efficient choice at high speeds.

No. 6:. Bolt-ons and pour-ins
Most of these devices and additives simply don't work. 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? And if there was a simple fix, everyone would already know about it?