Why Fuel Economy Myths Stick Around

Gas is one of the biggest ongoing costs of owning a car — right up there with insurance and maintenance. So it makes sense that drivers are always looking for ways to stretch a tank further. The problem is that a lot of the "tips" floating around are outdated, misunderstood, or simply wrong, and following them can quietly drain your wallet instead of protecting it.

Some of these myths date back to older engine technology. Others come from half-true ideas that got exaggerated over time. Either way, the result is the same: families spend money they don't need to spend, or skip habits that would actually help. See how fuel costs fit into the full picture of car ownership in our look at the true cost of owning a car.

Myth

You need to warm up your engine for several minutes before driving, especially in cold weather.

Fact

Modern fuel-injected engines warm up faster by being driven gently than by idling in the driveway.

This advice made sense decades ago when carbureted engines needed time to reach operating temperature before they'd run smoothly. Today's engines use electronic fuel injection and reach optimal temperature much more quickly under light load. Extended idling in the driveway wastes fuel, adds wear, and in cold climates can actually wash oil from cylinder walls. A 30-second idle to clear frost is reasonable; five minutes is not necessary.

Myth

Using premium fuel in any car will improve performance and fuel economy.

Fact

Premium fuel only benefits engines specifically engineered to require or recommend it.

Premium gasoline has a higher octane rating, which helps prevent "knock" (uncontrolled combustion) in high-compression engines. If your owner's manual says "regular unleaded," putting premium in the tank provides no measurable benefit — you're simply paying more per gallon for nothing. Check your manual: it will say "required" or "recommended" if premium matters for your engine. "Required" means use it; "recommended" means regular will work but the engine may perform slightly better with premium.

Myth

Coasting downhill in neutral saves gas because the engine isn't working.

Fact

In most modern cars, keeping the car in gear while coasting actually cuts fuel delivery to near zero.

When you lift off the accelerator while in gear, the engine's computer in most fuel-injected vehicles cuts fuel injection almost entirely — the wheels are spinning the engine rather than the other way around. Shift into neutral and the engine has to use a small amount of fuel just to keep itself running at idle. There's also a safety consideration: being in gear gives you better control and faster access to engine braking. Check your vehicle's documentation if you're unsure about its specific behavior.

Myth

Fuel economy additives and supplements sold at auto parts stores meaningfully improve mileage.

Fact

Independent testing has generally found little to no consistent fuel economy benefit from aftermarket fuel additives.

The U.S. Environmental Protection Agency has evaluated a wide range of fuel economy devices and additives over the years and found that most provide little or no improvement. Modern gasoline already contains detergent additives required by the EPA. If your vehicle is running poorly, the right fix is diagnosing the actual problem — not adding a bottle of something to the tank. Save that money for a proper tune-up if your maintenance is overdue.

Myth

Filling up in the morning gets you more gas because cold fuel is denser.

Fact

Fuel is stored underground where temperature stays fairly constant, so the time of day makes a negligible difference.

The idea is that liquid expands with heat, so cooler fuel would be denser and give you more energy per gallon. While this is technically true in principle, gasoline at retail stations is stored in underground tanks that maintain a nearly constant temperature year-round. The small surface-level temperature variation that does occur results in a difference too tiny to measure at the pump. Don't reorganize your schedule around this one.

Habits That Actually Move the Needle

Once you've cleared out the myths, the real fuel-saving habits are pretty straightforward — and none of them require a special product or trick.

~0.5%

Fuel economy lost per 1 PSI of underinflation

The U.S. Department of Energy estimates that underinflated tires can lower gas mileage by roughly 0.5% for every 1 PSI drop across all four tires.

Up to 30%

Fuel economy impact of aggressive driving

The U.S. Department of Energy notes that aggressive driving — rapid acceleration and hard braking — can lower highway fuel economy by up to 30% compared to smooth, consistent driving.

  • Keep tires properly inflated. Check the recommended pressure on the sticker inside your driver's door — not the number on the tire itself. Check monthly, since pressure drops about one PSI for every 10°F drop in temperature.
  • Drive smoothly. Hard acceleration and late braking burn significantly more fuel than gradual, consistent speed changes. On the highway, use cruise control when conditions allow.
  • Reduce unnecessary idling. If you're parked and waiting for more than a minute or two, turning off the engine generally uses less fuel than idling.
  • Follow your vehicle's actual maintenance schedule. A dirty air filter or worn spark plugs can hurt efficiency over time. Your owner's manual is the most reliable guide for your specific vehicle.

Don't Skip Tire Pressure Checks in Winter

Tire pressure drops roughly 1 PSI for every 10°F decrease in outside temperature. A tire that was properly inflated in October may be noticeably underinflated by January. Low pressure hurts fuel economy, increases tire wear, and can affect handling. Check pressure monthly and always when there's a significant temperature shift — not just when the warning light comes on.

These habits won't double your mileage overnight, but they can add up to real savings across thousands of miles — which is where car costs are actually measured. Fuel spending is just one piece of a larger household budget; for a broader look at managing household costs, see home budgeting strategies that can help families plan ahead.