10 Reasons Your Car is Using More Fuel Than Usual

When your car starts using more fuel than usual, the cause is usually simple and often costs little or nothing to fix. Many of the common culprits are things you can check yourself in a few minutes, such as soft tyres or a roof box you forgot to take off. The faults that do need a garage tend to come with a second warning sign.

Below are the 10 most common reasons your car’s miles per gallon (MPG) has dropped, starting with the free checks, plus how the speed of the drop can point you to the likely cause.

Has Your Fuel Economy Dropped Suddenly or Gradually?

How quickly the change happened is your best clue. A sudden drop usually points to a single fault, while a slow slide is more often down to the season, your journeys or a car that's due a service.

Things You Can Check Yourself

These four cost little or nothing to rule out.

1. Your Tyre Pressures Are Too Low

Soft tyres flatten where they meet the road, so the engine works harder to keep them rolling, a bit like pushing a bike with a half-flat tyre. Pressures usually creep down unnoticed, but a slow puncture or a cold snap can drop them within a tank or two.

It’s more common than you might think: in March 2026, TyreSafe warned that more than half of tyres on UK roads may be underinflated, and that a 10% drop in pressure can increase fuel consumption by around 2%.

Check your tyre pressures monthly with the tyres cold, using the figures in your handbook, on the driver's door frame or inside the fuel filler flap.

2. You're Carrying Extra Weight or a Roof Box

A heavy boot means your car uses more fuel every time you pull away, and roof boxes, bike racks and roof bars add drag. The Energy Saving Trust recommends taking them off when you're not using them, as the extra fuel cost is highest at speed.

3. The Weather Has Turned Colder

Some of the drop you notice from October onwards is normal, as a cold engine runs on a richer fuel mixture until it warms up and the heater fan, heated screen and lights draw more power.

If a modest drop arrived with the cold and the car feels normal, it's a seasonal issue.

4. Your Journeys or Driving Style Have Changed

A new commute or weeks of roadworks can change your MPG as much as a fault, because short trips and stop-start traffic burn more fuel.

Speed matters too, and the Energy Saving Trust says a car uses around 18% more fuel at 75mph than at 60mph. Small habits help, from planning more fuel-efficient journeys to ignoring the fuel-saving myths that do nothing for your MPG.

Faults a Garage Should Check

If the easy checks don't explain it, these six causes need a garage, and most come with a second symptom.

5. A Brake is Sticking or Dragging

A brake caliper that seizes, usually through corrosion, keeps the pad rubbing on the disc, like driving with the handbrake slightly on.

Look for a burning smell after a drive, the car pulling to one side or heat you can feel coming off one wheel when you hold your hand near it. Don't touch the wheel itself, as it can burn.

A sticking brake also affects how well your car stops and can pose a safety concern, so you should get it checked soon.

6. Your Wheels Are Misaligned

A pothole or a kerb can knock your wheels out of line, so they scrub slightly sideways instead of rolling straight. While the fuel penalty is usually small, the bigger cost is extra tyre wear so it’s still worth aligning your wheels sooner rather than later.

Look for uneven tyre wear on the inner or outer edge, an off-centre steering wheel or a car that drifts on a flat road.

7. Your Car is Overdue a Service

Worn spark plugs can cause misfires on a petrol engine, and old or incorrect oil adds friction. Using the oil grade your handbook specifies keeps the engine running efficiently.

A service tackles these small drains in one visit and gives a mechanic the chance to check for other faults that may be impacting fuel economy.

8. A Faulty Oxygen (Lambda) or Airflow Sensor

The lambda sensor measures oxygen left in the exhaust, and the mass airflow (MAF) sensor measures the air coming in. As these tell the engine's computer how much fuel to inject, the engine can get more fuel than it needs if either gives false readings, like a cook who can't taste the food and keeps adding salt.

A sensor fault commonly triggers the engine management light, often with rough idling or hesitation.

9. Your Thermostat is Stuck Open or an Injector is Leaking

A thermostat stuck open stops the engine reaching its normal temperature, so it keeps running the richer mixture it uses when cold. The giveaways are a temperature gauge that sits lower than usual, a heater that only blows lukewarm air and, on many cars, the engine management light.

Worn or leaking fuel injectors let in more fuel than they should, often with rough running or misfires. If you can smell petrol or diesel in or around the car, stop driving and get it checked, as a leak is a fire risk.

10. Diesel Only: Your DPF is Regenerating More Often or Blocking

A diesel particulate filter (DPF) traps soot and burns it off in a process called regeneration. Long, fast runs do this naturally, but if you mostly do short trips, the car injects extra fuel to heat the filter instead, which shows up as lower MPG, a fan that runs after you switch off or a higher idle.

If regenerations keep getting interrupted, the DPF warning light comes on, and a blocked DPF needs a clean as soon as possible to stop it becoming a bigger repair.

When to Get Your Car Checked

Most fuel drops have a simple explanation, so there's no need to panic. Book an appointment at a local garage if the extra fuel use comes with any of these:

• A fuel smell. Stop driving and get it checked straight away.

• The engine management light or, on a diesel, the DPF light.

• A pull to one side, a burning smell or a hot wheel.

• A low temperature gauge and a lukewarm heater.

• Black smoke from the exhaust.

• A sharp drop you can't explain, such as 50mpg falling to 40mpg on the same journeys.

Find a Garage to Get It Checked

If you can't pin down the cause, booking a car service is the sensible place to start.

Enter your reg and postcode to compare prices, reviews and availability through BookMyGarage to find the right garage for your needs in seconds. Most importantly, there’s no pre-payment required to make a booking*, and you pay the garage directly once the work's complete.

We're here to make things simple and stress-free, so you can book with confidence and look forward to the results.

*Some mobile technicians (that come out to you) may require an upfront payment or commitment, please check this with them first.