Poor Fuel Economy
Higher fuel consumption than usual can come from driving conditions, tyre pressure and load, or from faults such as a stuck-open thermostat, a slow oxygen sensor or dragging brakes.
Normal risk
Not a safety issue, but a sudden increase is worth checking.
Short answer · Why is my car using more fuel?
Rule out the simple things first: tyre pressures, roof boxes, short winter trips and air conditioning use all increase consumption. If it rose suddenly, look at warning lights and fault codes. A thermostat stuck open, a slow oxygen sensor, a rich mixture or a dragging brake are common faults.
Safe checks you can do
- Check tyre pressuresLow pressure increases rolling resistance.
- Measure consumption over a full tankTrip computer values can vary; compare like for like.
- Check for warning lightsFault codes point to engine causes.
Questions that narrow it down
- Did it increase suddenly?Points to a fault.
- Mostly short trips in cold weather?Normal increase.
- Is one wheel hot after driving?Dragging brake.
Possible causes
Listed without ranking. Use the questions above to see which ones fit your car.
- Low tyre pressureMore rolling resistance.
- Thermostat stuck openEngine stays cold.
- Oxygen sensor or rich mixtureToo much fuel.
- Dragging brakeConstant resistance.
- Driving conditionsShort trips, cold, heavy loads.
Questions about Poor Fuel Economy
How much does air conditioning add?
It varies by car and weather; it is usually noticeable in town and less on the motorway.
Does premium fuel save fuel?
Only if the engine is designed for it.