Fuel can take up a fair share of your weekly budget, especially if you rely on your car and have little choice about the trips you make. Even when your route stays the same, the pump price can make a difference. A gap of 5p per litre works out at £2 on a 40-litre fill.
The cost also depends on how much fuel your car uses. Traffic, road conditions and the length of each trip can all affect how far a tank takes you.
How much could a lower pump price save me?
The saving depends on the price gap and how many litres you buy. If two stations sell the same grade of fuel and one charges 5p less per litre, the difference comes to:
- 50p on a 10-litre top-up
- £1 on a 20-litre fill
- £2 on a 40-litre fill
Some fuel vouchers come with a minimum spend in store. The saving at the pump depends on how many litres you buy.
If two stations are on your usual route, you can compare local petrol and diesel prices for the grade your car uses. If the cheaper station means a trip out of your way, the extra miles use fuel and reduce the saving.
Is premium fuel worth the extra cost?
That depends on the fuel grade your car needs. Your handbook lists the grades that suit your engine. Some cars need a specific grade, so two prices on the same forecourt may be for different products.
For example, if a premium grade costs 10p more per litre, a 40-litre fill costs £4 more. Whether that grade offers a benefit for your car depends on the engine. The handbook sets out which grade the car maker recommends.
How do speed, gears and traffic affect fuel use?
A car tends to use more fuel in stop-start traffic than on a clear run. Each time the queue moves, the engine uses fuel to bring the car back up to speed. That can change the cost of a familiar trip even when you cover the same miles.
On an open road, higher speeds can also mean higher fuel use. In a manual car, the gear makes a difference because the engine can run at different speeds even when the car is travelling at the same pace. The gear that suits a flat road may differ from the one the car needs on a hill.
The AA includes smooth driving among the factors that can affect fuel use. How much difference it makes on any one trip depends on the road, the weather and the traffic.
Does air conditioning use more fuel than opening a window?
It depends on the car, its speed and the conditions. Air conditioning draws power from the engine in a petrol or diesel car. At higher speeds, an open window can create more drag as air flows around the car. There is no single speed at which one option costs less for every driver.
Air conditioning can also help keep the cabin comfortable and clear mist from the glass. When a windscreen mists up, a clear view of the road takes priority over a possible fuel saving.
Can tyre pressure, roof boxes and extra weight affect fuel costs?
Yes. Tyres with too little air can increase fuel use. Your handbook gives the right pressure for your car and may list a different figure for a full load. When checking tyre pressure, you can compare the reading from cold tyres with the figure in the handbook.
A roof box affects fuel use in a different way. As the RAC explains, even an empty roof box can increase wind resistance. This means the engine has to work harder to keep the car moving at the same speed.
Weight can also affect fuel use. For example, a suitcase left in the boot after a holiday adds to the load on later trips.
Why can short trips use more fuel per mile?
A cold engine uses more fuel as it warms up. On a short trip, the engine may still be warming up when you arrive. This can help explain why your car shows a lower average MPG on a short local trip than on a longer drive.
Even on the same route, fuel use can vary. A clear run to a morning appointment may use less fuel than the drive home through heavy traffic.
Does a parked car use fuel while the engine is running?
Yes. A petrol or diesel engine still uses fuel when the car is parked and the engine is running. This is called idling. It can help explain why two trips of the same length use different amounts of fuel.
Some cars have a stop-start system that can pause the engine when the car comes to a stop. When the system does this depends on the model and the conditions.
Rule 123 of the Highway Code covers engine idling on public roads, including the distinction between a parked car and one waiting in traffic.
How does servicing fit into fuel costs?
A regular service helps keep a car running as intended. The handbook sets out when work is due and gives the grade of engine oil for your car. Both can vary by make, model and engine.
What a car service includes depends on the type of service and the miles the car has covered. It may include an oil change and checks on filters and other parts.
A single costly fill tells you little about whether a service is due. The price per litre may have risen, or your last few trips may have been shorter than usual. Your service record shows when work was last done, while the handbook sets out the next interval.
How can I tell if my car is using less fuel?
Your car’s miles per gallon (MPG) tells you how far it travels on a gallon of fuel. A higher MPG means the car used less fuel per mile. If your dashboard shows an average, trips of much the same length and type are easier to compare.
For example, suppose your car averaged 40 MPG on your usual drive last week and 44 MPG on the same drive this week. It used less fuel per mile this week. A motorway trip and a short drive through town would be harder to compare because the conditions differ.
Cost per mile answers a different question. If a stretch of 150 miles used £30 worth of fuel, the fuel cost was 20p per mile. That figure takes the pump price into account. MPG measures how far the fuel took you, whatever you paid for it.
What if I’m already thinking about replacing my car?
Fuel is one part of the cost of another car. A model that uses less fuel on your usual trips could cost less in fuel over the same distance. Other costs may include insurance, servicing, repairs and monthly payments if you use finance.
Go Car Credit is a direct lender of bad credit car finance. We offer Hire Purchase and assess applications ourselves.
If your application meets our minimum criteria, we use a soft credit search to review it. This does not affect your credit score.
We only carry out a hard search once you have signed the agreement and it is ready to go ahead. This records the agreement on your credit file. All finance is subject to status and affordability.
