When a vehicle starts using more fuel than it used to, the cause is more often ordinary than mysterious. The good news is that most of the common causes are cheap to check. Work through them from the simplest to the most involved, and change one thing at a time so you know what made the difference.
1. Driving style and speed
How a vehicle is driven is one of the biggest factors in how much fuel it uses. Hard acceleration, late braking, high cruising speeds and long idling all raise consumption, and the effect is larger in stop-and-go traffic and at highway speed than in steady, moderate driving. Government fuel-economy guidance puts smooth, anticipatory driving and sensible speeds at the top of its advice for this reason.
2. Tire pressure and condition
Under-inflated tires roll with more resistance, so the engine works harder for the same distance. Check the pressure when the tires are cold, against the figure on the vehicle’s placard or in the manual, and check it regularly: tires lose pressure slowly, and heat changes it. Worn tires and wheels that are out of alignment, or a brake that drags slightly, have a similar effect.
3. Extra weight and drag
Every kilogram carried costs a little fuel, and so does air resistance. Remove loads you do not need, and take off roof racks and boxes when you are not using them. For work vehicles, check that the load really is the load you intend to carry.
4. Air conditioning and hot weather
In the Saudi climate the air conditioner runs for much of the year, and it takes power from the engine. This is normal, but it explains why consumption in summer can differ from consumption in winter. Parking in shade and ventilating a hot cabin before switching on the air conditioner can help.
5. Short trips and cold engines
An engine uses more fuel until it reaches its normal operating temperature, so many short trips use more fuel per kilometre than one longer trip. Combining errands into one journey helps.
6. Maintenance that has been put off
- Air filter. A badly clogged filter restricts airflow, which matters most in dusty conditions.
- Spark plugs and ignition on gasoline engines: worn parts can lead to incomplete combustion.
- Fuel filter and water separator on diesel engines.
- Oil. Using the grade the manufacturer specifies and changing it on schedule keeps friction where it should be.
Follow the service schedule in your owner’s manual, which is written for your engine.
7. Sensors and warning lights
Modern engines rely on sensors to set the fuel mixture. A faulty oxygen sensor or a similar fault can make an engine use more fuel without any obvious symptom except the warning light and the fuel gauge. If a warning light is on, have the fault codes read rather than waiting.
8. Fuel quality
Contaminated or poor-quality fuel, and water in diesel, can disturb combustion. Buy from busy, reputable stations, and if you suspect a bad tank, mention it to your workshop.
Before you conclude anything, measure
A feeling that a vehicle is thirstier is easy to get wrong: a hotter month, a heavier load or a different route can explain it. Measure over several tankfuls before and after any change, as described in our guide to measuring fuel consumption.
Sources and further reading
- U.S. Department of Energy, FuelEconomy.gov: Gas mileage tips.
- U.S. Department of Energy: Fuel economy tips consumer guide (PDF).
- U.S. Department of Energy, Alternative Fuels Data Center: Gas-saving tips (PDF).
General information for orientation. Results depend on the vehicle, its condition, fuel and how it is driven; this guide makes no promise about any individual vehicle.
