We posted these before, but are some new things that make them not true.


6 gas-saving myths
Sure you want to save gas, but there's a lot of bad advice on how to do it. Some of it makes no difference, and some of it can wind up costing you.


By Peter Valdes-Dapena, CNNMoney.com staff writer
Last Updated: May 13, 2008: 3:11 PM EDT
NEW YORK (CNNMoney.com) -- 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:

#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, so there's little, if any, benefit, to getting up early to pump gas.

#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.

While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.

#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 if they stick with it. Really, they're paying more money for nothing.

Even cars for which premium is recommended won't suffer with regular fuel. Modern engine technology comes to the rescue again. When sensors detect regular instead of premium fuel, the system automatically adjusts spark plug timing. The result is a slight reduction in peak horsepower - really, you'll never notice - but no reduction in fuel economy.

#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. As speed increases, drag becomes more of an issue, making A/C use the more efficient choice at high speeds.

At most speeds and in most vehicles, A/C use drains slightly more fuel than driving with the windows down, contends David Champion, head of auto testing for Consumer Reports. "My final take on is that it's very close," says Phil Reed, consumer advice editor for Edmunds.com. "It's hard to measure the difference and every vehicle is different."

The best choice - if temperature and humidity allow - is to keep the windows