Top 10 Reasons Your Fuel Consumption Has Increased

Fuel consumption gone up and not sure why? Before guessing, go through this list — most causes are straightforward once you know what to look for.

1. Winter and Cold Weather

Cold engines run rich until they reach operating temperature. The longer you warm up, the more fuel you burn before even moving. Add winter tyres into the equation — they have higher rolling resistance than summer tyres, which means higher load on the engine and higher consumption across the board.

Tyre size matters too. A different tyre diameter changes the load on the drivetrain during acceleration and directly affects fuel consumption.

2. Change in Driving Style

Started driving more aggressively? More highway kilometres, more overtaking, more full-throttle acceleration? Consumption follows driving style directly. If your habits changed, your numbers will change with them.

3. Fuel Quality

Low-quality fuel burns less efficiently, which means the engine needs more of it to produce the same power. This is especially noticeable on petrol engines with knock sensors — the ECU retards ignition timing to prevent knocking on poor fuel, which reduces efficiency.

4. Clogged DPF or Catalytic Converter

A blocked diesel particulate filter or a degraded catalytic converter increases exhaust backpressure significantly. The engine has to work harder to push gases out, which costs fuel. A Check Engine light is often the first sign — don't ignore it.

5. Dirty Air or Fuel Filter

A clogged air filter restricts the airflow the engine needs for combustion. A dirty fuel filter reduces fuel pressure and flow. Either way, combustion efficiency drops and consumption goes up. Both filters are cheap to replace and easy to overlook.

6. Faulty Injectors

Worn or dirty injectors do not atomize fuel properly. The mixture burns less completely, power drops, and the ECU compensates by injecting more fuel. On diesel engines this can also cause black smoke under load.

7. Extended Time in Traffic

Stop-and-go driving is the most fuel-inefficient operating mode for an internal combustion engine. Frequent acceleration from standstill, engine idling, and low-gear driving all push consumption up. If your daily commute got worse, your numbers will reflect it.

8. Open Sunroof or Low Tyre Pressure

A fully open sunroof at motorway speeds adds aerodynamic drag equivalent to carrying extra load. Underinflated tyres increase rolling resistance noticeably — check your tyre pressures regularly, especially in winter when pressure drops naturally with temperature.

9. Manufacturer Figures Are Not Real-World Numbers

The official fuel consumption figure in your vehicle's documentation is measured under controlled lab conditions — not in real traffic. A car listed at 6 L/100km will typically consume 8–9 L/100km in normal use. If you bought the car expecting the passport figure, the "increase" may simply be reality setting in.

10. Additional Electrical Loads

Air conditioning is the biggest one — it can add 1–2 L/100km on its own. Audio systems, LED light bars, heated seats, power steering pumps — all of these draw power from the engine. The more electrical load, the higher the fuel consumption, especially at low speeds where the alternator runs less efficiently.

These are the most common causes — but the list does not end here. If you have ruled out the obvious and consumption is still high, the next step is a proper diagnostic scan. A fault code that seems unrelated to fuel economy can often be the root cause.

Have a persistent Check Engine light? Start with our OBD-II database — look up the code before visiting a workshop.