"Premium fuel gives better mileage"
Only if your car calls for it. Premium has a higher octane rating, which resists knock in high-compression or turbocharged engines designed for it. In a car designed for regular, premium gives no meaningful mileage or power benefit. Check the owner's manual or the label inside the fuel door, and use what it says.
"This gadget will boost your MPG"
Add-on devices sold to save fuel include magnets on fuel lines, air intake vortex devices and plug-in "fuel savers". The US Environmental Protection Agency has tested many such products over the years and found that almost none gave any real improvement, and some could harm the engine or increase emissions. Be wary of large claims, especially when the only evidence is personal stories.
"Coasting in neutral saves fuel"
On a modern fuel-injected car, coasting in gear with your foot off the accelerator usually cuts fuel to the engine almost completely. In neutral the engine has to idle, which uses fuel. Coasting in neutral also reduces your control of the car and is illegal in some places. Stay in gear.
"Let the engine warm up for ten minutes"
Older carbureted engines needed it. Modern engines are ready to drive after a short wait, and they warm up faster when driven gently than when idling. Long warm-ups burn fuel for zero miles. In freezing weather, clear the windows completely before driving, whatever it takes.
"Fill up early in the morning, when fuel is denser"
Fuel is stored in underground tanks where the temperature barely changes during the day. Any difference from the time of filling is too small to notice.
"Air conditioning always beats open windows"
It depends on speed. At low speeds, open windows usually cost less. At highway speeds, the drag from open windows can cost as much as the AC or more. In hot weather, comfort and alertness come first.
"A new air filter will fix your mileage"
It used to be true for carbureted engines. On modern fuel-injected engines, a clogged air filter mostly reduces acceleration. Replace it on schedule, but don't expect a mileage jump. See maintenance that matters.
"Small cars always beat big ones"
Size matters, but so do the powertrain, aerodynamics and how the car is driven. A hybrid midsize car can use less fuel than a small car with a conventional engine, especially in town. Compare official ratings for the vehicles you're considering rather than guessing from size.
What actually works
| Myth | What works instead |
|---|---|
| Premium fuel | The fuel grade in your manual |
| Fuel-saving gadgets | Smooth driving and moderate highway speeds |
| Coasting in neutral | Lifting off early while in gear |
| Long idling warm-ups | Driving gently for the first few minutes |
| Overinflated tires | Tires at the door-jamb placard pressure |
Myths FAQ
Does drafting behind a truck save fuel?
Following very closely reduces drag, but it is dangerous. You can't see the road ahead, and you have no time to react if the truck brakes. Don't do it.
Does running the tank low save weight?
A full tank adds some weight, but the effect is small. Running very low on fuel risks running out and, in some cars, can strain the fuel pump, which uses the fuel around it for cooling.