Topping off the tank saves on fuel.
Fact: In reality, topping off can actually send gas back to the station instead of into your car. The gas nozzle automatically shuts off when your tank is full, so any additional gas you try to add will be drawn into a vapor recovery system and back into the station’s storage tanks. In addition to paying for gas you’re not actually receiving, you may damage you car’s evaporative emissions system.
Warming up before driving is necessary.
Fact: That was true back in the days of carburetors and chokes, but it isn’t the case with modern fuel-injected, electronically controlled drivetrains. Engines are most efficient when they’re at regular operating temperature, and the fastest way to reach that point is to drive immediately after starting the car.
Driving with windows open hurts fuel economy.
Fact: 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. While testing this theory in a Honda Accord, the effect of opening the windows at 65 mph had little to no effect on MPG.
Idling uses less fuel than turning your car off and back on.
Fact: In the same way that turning off the lights when you leave a room saves electricity, turning your car off when you’re stopped is usually the best option. It’s been said that turning the car off and on wastes more fuel than idling, but nothing could be further from the truth. Idling wastes gas in a big way. According to the EPA, idling engines can use one-quarter to one-half a gallon per hour, costing you 1 to 2 cents per minute. Any time you plan on idling for more than a minute, it’s best to turn the engine off.
Turning the A/C off saves gas.
Fact: It depends on the aerodynamics of your vehicle. The myth comes from the old days when they had really old parts of the older cars… there isn’t absolutely no difference but it is really, really small. You won’t see a big change in your fuel economy, meaning don’t worry too much about running that A/C.