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Fuel economy & running costs
Why Is My Car Using More Fuel Than Usual?
A rising fuel bill does not automatically mean something is broken. Traffic, short trips, tyre pressure and changing driving habits can all affect consumption. The useful first step is to confirm whether your vehicle is actually using more fuel over several fill-ups.
Short answer: Compare fuel use across similar journeys before assuming there is a mechanical problem. If a warning light, fuel smell, leak, unusual smoke or poor running accompanies the change, arrange a professional check promptly.
First, measure the change instead of guessing
A dashboard economy estimate is useful, but it can fluctuate after short journeys or long periods idling. A more dependable trend comes from recording the distance travelled and litres added across several comparable fill-ups.
Example: 420 km driven using 35 litres = 12.0 km/L (or about 8.33 L/100 km). If a comparable period later gives 10.5 km/L, investigate changes to driving patterns and maintenance before drawing conclusions.
Use the free GEMENEV fuel consumption and cost-per-km calculator to check your own figures.
10 common reasons fuel consumption increases
1. More stop-and-go driving
City congestion means more acceleration, braking and idling for every kilometre travelled. Compare city journeys with similar city journeys, not with an open-road trip.
2. Shorter journeys
A series of brief trips can be less efficient than one longer journey. A colder engine and repeated starts affect typical petrol or diesel vehicles; hybrid behaviour varies by model.
3. Tyres below the recommended pressure
Underinflated tyres increase rolling resistance. Check pressures when the tyres are cold and use the vehicle placard or owner’s manual, not the maximum printed on the tyre sidewall.
4. Sudden acceleration and hard braking
Driving style can make a noticeable difference. Smooth, lawful driving generally wastes less energy than repeated heavy acceleration and braking.
5. Changes in air conditioning use
Hotter weather and heavy air-conditioning use can alter fuel economy, especially in slow traffic. Compare weather and trip conditions before blaming the engine.
6. Extra weight and roof accessories
Carrying unnecessary cargo or leaving an external roof rack installed may increase fuel demand. Aerodynamic drag becomes particularly relevant at higher speeds.
7. Delayed or incorrect maintenance
Some engine faults, neglected maintenance items or incorrect engine-oil specifications can affect efficiency. Follow the manufacturer’s service schedule rather than replacing parts based on an article alone.
8. A fault recorded by the engine-management system
An illuminated check-engine light may indicate a sensor, ignition, emissions or fuel-system issue. A technician can read fault information and diagnose its cause; the light by itself does not identify a specific failed part.
9. Brake drag or tyre-related resistance
A sticking brake or abnormal tyre wear can create resistance. If the car pulls, smells hot, feels unstable or brakes differently, stop when safe and get it inspected rather than continuing to test it.
10. Measurement or fuel-fill differences
A partial fill, inaccurate odometer input, changing fuel blends or differences in how a tank was filled can skew a single result. Compare multiple records.
A practical fuel-use comparison checklist
| Compare | Useful question | Next step |
|---|---|---|
| Driving route | Did you spend more time in traffic? | Compare similar routes |
| Tyre condition | Are cold pressures at the specified level? | Follow vehicle placard / manual |
| Service history | Is any manufacturer-scheduled service overdue? | Check service records |
| Warning signs | Any warning light, leak, unusual smell or poor running? | Arrange professional diagnosis |
| Fuel records | Is the change consistent over multiple fill-ups? | Keep recording mileage and litres |
Build a fuel-cost baseline you can trust
Record the date, odometer, litres, total spend and route type for several fill-ups. Then compare km/L and cost/km over time. Avoid judging the vehicle from one unusual journey. The service history template helps you note when tyres, filters and other maintenance items were checked.
Worked example: same distance, different fuel use
Imagine two comparable 420 km driving periods. This example uses an illustrative price of 300 currency units per litre, not a current fuel-price quotation. It shows why small changes in fuel economy can affect total running cost.
| Measure | Earlier period | Later period |
|---|---|---|
| Distance | 420 km | 420 km |
| Fuel used | 35 litres | 42 litres |
| Fuel economy | 12.0 km/L | 10.0 km/L |
| Consumption | 8.33 L/100 km | 10.0 L/100 km |
| Fuel cost per kilometre | 25 currency units | 30 currency units |
| Total fuel cost | 10,500 currency units | 12,600 currency units |
Frequently asked questions
Does using the air conditioner increase fuel consumption?
It can, particularly in heavy traffic and on hot days. The impact depends on the vehicle and conditions, so compare like-for-like trips.
Can low tyre pressure affect fuel economy?
Yes. Underinflated tyres increase rolling resistance. Use the cold-pressure recommendation on your vehicle’s placard or in the manual.
What if fuel consumption suddenly becomes much worse?
If the change persists, or comes with warning lights, poor running, unusual smells or leaks, arrange a qualified inspection instead of guessing which part needs replacement.
Fuel is one part of your full vehicle budget
A change in kilometres per litre changes your running cost, but planned servicing and repair reserves matter too. Use the free annual car-maintenance budget worksheet to estimate these costs separately. When you record the vehicle’s fuel spending and service history, avoid confusing a one-off bill with a longer-term trend.
Sources and further reading
These resources provide general automotive information. Check the vehicle's handbook for model-specific guidance.
This guide is educational content from GEMENEV, prepared with AI assistance and public reference material. It is not a mechanical diagnosis or a replacement for professional vehicle safety advice. Always follow the owner's manual and advice from qualified technicians.