Start with the owner's manual
The maintenance schedule in your owner's manual lists what to check and when, by miles or by time. It's written for your engine, so follow it ahead of any general advice, including ours. Many cars also show service reminders on the dashboard.
What matters for mileage
| Item | Effect on mileage | What to do |
|---|---|---|
| Tire pressure | Low tires cost a little at every speed | Check monthly, set to the door-jamb placard. See tire pressure. |
| Motor oil grade | Using the specified grade can help by about 1 to 2 percent over a heavier one | Use the viscosity grade listed in the owner's manual. |
| Check engine light | Some faults, such as a failing sensor, can hurt mileage a lot | Have it diagnosed promptly by a qualified mechanic. |
| Wheel alignment | Small effect, plus uneven tire wear | Have it checked if the car pulls or tires wear unevenly. |
| Dragging brakes | A sticking caliper acts like a light brake on all the time | Watch for a pull to one side, a hot wheel or a burning smell, and see a mechanic. |
| Engine air filter | On modern fuel-injected cars, mainly affects acceleration | Replace on schedule or when dirty. |
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Motor oil
Modern engines are designed around a particular oil viscosity, shown as a grade such as a number, a W and another number. Thinner grades reduce internal friction, and US government guidance says using the recommended grade can improve mileage by about 1 to 2 percent compared with a heavier oil. Oils labeled as energy conserving carry friction-reducing additives. Change the oil on the schedule in your manual.
The check engine light
A lit check engine light means the car's computer has found a fault. Some faults, such as a failing oxygen sensor or a misfire, can make the engine run rich and burn noticeably more fuel. A flashing light usually means a serious misfire that can damage the catalytic converter, so reduce speed and get help promptly. Many parts stores and all repair shops can read the stored code, and a qualified mechanic can find the cause.
The engine air filter, updated
Older advice said a dirty air filter wrecks mileage. That was true for carbureted engines. On modern fuel-injected engines with computer control, testing has found little effect on mileage, though a clogged filter does reduce acceleration. Replace it on schedule anyway. It protects the engine from dust.
Other items worth a look
- Spark plugs. Worn plugs can cause misfires. Most modern plugs last a long time, so follow the manual's interval.
- Fuel cap. A loose or damaged cap can trigger the check engine light and let fuel vapor escape. Tighten it until it clicks.
- Wheel bearings and brakes. Anything that makes a wheel hard to turn costs fuel. Unusual noise or heat from a wheel needs a mechanic.
Brakes, steering, suspension, fuel lines and high-voltage hybrid or electric systems are safety-critical. Leave that work to a qualified mechanic.
Maintenance FAQ
Will a tune-up improve my mileage?
The old-style tune-up mostly belongs to older engines. On a modern car, fixing a real fault, such as a misfire or a bad sensor, can help a lot. Routine service on a car that's running well usually keeps mileage where it is rather than raising it.
Do fuel system cleaners help?
Most gasoline sold in the US already contains detergent additives. If you suspect a fuel system problem, have it diagnosed rather than guessing. See our page on fuel-saving myths.