With gasoline prices nearing record levels, many drivers are trying to adopt ways to reduce the amount of gas their car uses. That's a noble goal, but don't fall for some common myths that, in some cases, will end up costing you money.

The average national price for a gallon of regular unleaded gas was $3.04 Wednesday, according to AAA. Crude oil, which closed at $87.34 a barrel in trading on the New York Mercantile Exchange, has flirted with the $100-a-barrel mark in recent weeks. That is near the inflation-adjusted highs set in the early 1980s.

Here are 10 gas-saving myths that you should know to make sure you are truly saving money on gas, rather than putting money, time and effort into something that won't work:

1. Products claiming to increase gas mileage

: The Federal Trade Commission has tested more than 100 devices that claim to save gas -- some up to 25% -- and found not one that significantly improves gas mileage as claimed. In fact, the FTC found that some may actually

damage the car's engine. You can also see the test results of such devices by the

Environmental Protection Agency.

Consumer Reports

has also tested numerous products over the years that make the improved-mileage claim

and haven't found any that actually work.

2. Turn off the AC

: This is the classic debate that will keep people arguing for hours. According to a

Consumer Reports

test, there is

very little difference between driving with your windows down or with the air conditioner on at 65 mph on the highway.

Edmunds

came to a

similar conclusion.

3. Buy gas on Wednesday

: The theory is that if you buy gas on Wednesday, prices have come down from the weekend, when many gas stations elevate their prices in hopes of making a bit more profit from more people traveling. While a general rule would be to avoid buying on weekends, there are too many factors that come into play to rely on the Wednesday strategy. You are much better off looking at what gas stations are charging in your area through sites like

AAA's fuel price check,

GasBuddy or

Gas Price Watch to find the best price on a daily basis.

4. Idle away

: At one time, this may have been true, but with modern fuel-injection technology, it's no longer the case. Just as there is no longer a need to spend 10 minutes warming up your car on a cold morning, if you are going to be sitting for more than a half minute, you will save more gas by turning the engine off than letting it continue to run.

5. Sticker stats

: The rating that automakers provide for gas mileage should be taken with a grain of salt. Beginning with 2008 vehicle models, the Environmental Protection Agency

required fuel efficiency standards to be reported based on new test methods that better reflect actual driving conditions. Older models, however, may have derived their ratings via outdated or inaccurate methods.

While differences in manufacturer-devised MPG ratings will indicate one car is more fuel efficient than another, that is about all you can deduct from this number. You are better off looking at real-world mileage tests from

Edmunds

and

Consumer Reports

if you want a good idea of what gas mileage your car will really get.

6. Up your octane

: A higher grade of gas is not necessarily better for your car. Some higher-performance car engines need a higher octane level, which refers simply to how much the fuel can be compressed before it ignites. It's a myth that higher-octane fuel burns hotter and cleaner, and it will not improve an ordinary car's gas mileage. Your driver's manual will list the recommended level of octane, which will usually be the lowest.

7. Gas rebate cards save money

: This is one of those areas where you need to be very careful. On the face of things, getting a 3% to 5% rebate each time you purchase gas looks like a no-brainer, but this is not always the case. If you don't pay off the card in full each month, any savings on gas will immediately be taken away with interest charges. Some gas cards may come with yearly fees that can negate any savings. There also may be less expensive gas in your area that doesn't allow a credit card to be used. Run the numbers before assuming that a gas credit card will save money.

8. Buy a fuel-efficient car

: Many people believe that the best way to save gas is to purchase a fuel efficient car. While this will help, the truth is that the best way to save money on gas is to change your driving habits. Making basic changes to your driving habits

will save you a lot more money than changing to a fuel efficient car without changing your habits. Getting a fuel efficient car on top of changing your habits will be even a bigger bonus.

9. Gas up in the morning

: This myth is based on the science that gas is denser when it is cool out than in the heat of the day. The logic goes that purchasing gas in the morning, when it is cool, will mean you get more in your tank than if you buy it in the heat of the afternoon, because gas pumps measure volume and not density of the fuel. The problem is that the gas is stored in underground tanks, so the heat of the day has little effect on the gas temperature, meaning you can purchase gas at any time and get virtually the same amount.

But there is one reason you might want to buy gas in the morning. If you believe gas prices are going to be rising, most gas stations don't change their daily price until 8 a.m. or so, meaning you still can get the previous day's price in the early morning.

10. Overinflated tires will save gas

: The logic is that if underinflated tires waste gas and properly inflated tires get better mileage because of less tread contact on the road, over inflated tires would have even less tread contact, which would increase mileage.

Popular Mechanics

tested this theory and found that it didn't provide any added benefit and that it was

dangerous.

Increasing your fuel efficiency as much as possible is sensible, but make sure that you don't buy into the myths that can be dangerous and siphon your wallet.

Jeffrey Strain has been a freelance personal finance writer for the past 10 years helping people save money and get their finances in order. He currently owns and runs SavingAdvice.com.