1-Warming up: Letting your vehicle warm up before driving will be best for fuel economy. It will increase the gas mileage. But this theory is only for the cars in old times. Nowadays the manufacturers are designing such vehicles which can be driven within seconds after starting up.[irp]
2-Old cars: 10 or even more years old cars will experience the decrease in fuel economy if not properly maintained and become less efficient. The minor effect of age is on those cars which are properly maintained and are in good condition even if they are 10 or more years old.
3-Smaller cars: Another myth is that the fuel economy is better in smaller vehicles/cars. Somehow this conception is true but does not consider one hundred percent correct. Many bigger models are competitively fueling efficient than the smaller cars.
4-Manual transmission cars: This was true that the manual cars or vehicles are fuel efficient and automatic transmissions were dumb and unfit. This myth was also used to be true before the arrival of the modern technologies. This holdover from the good old days continues, but modern cars changed this misconception. Most automatics are designed to be more fuel efficient than the manual ones.
5-It takes more fuel to start a car than allowing it to idle: It is not correct that turning the car on and off will consume up to 10% more fuel. The advent of stop-start technology has proved enough that this is a myth. Therefore, one should turn off the engine of the car when sitting idle or still, apart from when waiting in traffic or in line. New engines start more easily and efficiently.
6-Premium gas yields better fuel economy: Better gas will yield better than regular ones. But if your car’s engine is designed for regular one then use the regular. You can’t have any benefit from better fuel and the premium gas does not provide any significant benefit or improved economy.
7-Replacing air filters will increase fuel economy: You may lose efficiency. This is a saying from the days of carbureted engines, and which are badly affected by dirty air filters. It is more than common sense and still generally recommended. But it does not mean that it saves fuel. It could possibly increase power for a freer breathing engine.
8-Bolt-on devices increase fuel economy: This is a controversial topic and a huge aftermarket business nowadays. These fuel additives or bolt on devices you could buy and install are not guaranteed despite assurances by the dealers. This myth can’t be true as the fuel injectors will insert the same amount irrespective of the fact that you have these devices in the fuel or not.
9-Government Tests: The federal government tests fuel economy for all cars or trucks. These tests are not practically applicable or possible, that is why some vehicles are not tested.[irp]
10-Fuel economy stickers: EPA window stickers are a form of guaranty on fuel economy. This might be true if they did not hear this line “your mileage may vary” enough times. The main purpose of EPA fuel economy is to evaluate and provide users with an unvarying and impartial way of comparing the comparative efficiency of vehicles.