YONKERS, N.Y. --- In its June issue, Consumer Reports debunks some fuel-saving myths after testing them in the real world.

Morning fill-ups. A common tip is to buy gasoline in the morning, when the air is cool, rather than in the heat of the day. The theory is that the cooler gasoline will be denser, so you will get more for your money. But the temperature of the gasoline coming out of the fuel nozzle changes very little, if at all, during any 24-hour stretch. Any extra gas you get will be negligible, Consumer Reports said.

Air conditioning vs. opening windows. Some people advise you not to run the air conditioner because it puts more of a load on the engine, which can decrease fuel economy. But others say that opening the windows at highway speeds can affect gas mileage even more by disrupting the vehicle's aerodynamics. Consumer Reports' tests showed that neither makes enough of a difference to worry about.

Using air conditioning while driving at 65 mph reduced a Camry's gas mileage by about 1 mpg. The effect of opening the windows at 65 mph was not even measurable.

A dirty air filter. Consumer Reports' tests indicated that driving with a dirty air filter no longer has any impact on fuel economy, as it did with older engines. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow causes the engine to automatically reduce the amount of fuel being used. Fuel economy didn't change, but the Camry used in the test accelerated much more slowly with a dirty filter.