How to Save Fuel While Driving: Practical UK Advice

Fuel is one of the few running costs a driver can genuinely control. The car's official figures are fixed, but real world consumption between two people driving identical cars on the same route can differ by a third, and almost all of that gap comes down to habits and maintenance rather than anything exotic.

The advice below is ordered roughly by how much difference it makes. Start at the top.

Where your fuel actually goes

Understanding what the engine is fighting makes the rest of this obvious. Fuel is consumed overcoming four things.

• Aerodynamic drag. Rises with the square of speed, so it dominates above roughly 50mph. This is why motorway speed matters more than almost anything else, and why roof boxes and open windows are expensive at speed.
• Rolling resistance. Mostly tyres flexing against the road. Under inflated tyres increase this measurably, and it matters most at low and moderate speeds.
• Accelerating mass. Every time you speed up you are buying kinetic energy with fuel, and every time you brake you throw it away as heat. Stop start driving is expensive because you keep repurchasing the same energy.
• Ancillaries and losses. The air conditioning compressor, alternator, power steering pump, and the enormous inefficiency of a cold engine before it reaches operating temperature.

Every tip below reduces one of those four.

How your driving style changes fuel use

Smooth, anticipatory driving is the single largest lever most people have, and it costs nothing.

• Look much further ahead. If you can see a queue, a red light or a roundabout 200 metres away, ease off now and arrive at walking pace rather than braking hard at the last moment. Energy you would have burned off in the brakes carries you forward instead.
• Accelerate progressively, not gently. This surprises people. Crawling away from a junction in a low gear at low throttle keeps the engine in an inefficient part of its range for longer. Firm but smooth acceleration up to your target speed, changing up early, is generally more efficient than dawdling.
• Brake less, not later. The goal is not to brake gently, it is to need the brakes less often.
• Keep a bigger gap. Sitting close to the car in front forces you to mirror every speed change they make. A larger gap lets you hold a steadier speed and absorb their fluctuations, which saves fuel and is safer.
• Do not coast in neutral. Modern injection systems cut fuel completely on the overrun when the car is in gear with your foot off the accelerator. In neutral the engine has to be fed to keep idling, so you are burning fuel and have less control of the car.
• Use cruise control on flat roads only. It holds a steadier speed than most people can on a level motorway. On hilly roads it reacts late and applies large throttle openings to hold speed up an incline, which uses more fuel than simply letting the speed drift down a few miles an hour.

What is the most fuel efficient speed?

Most cars are at their most efficient somewhere between 50 and 60mph in top gear, and consumption rises sharply above that. The engine is at a comfortable load, drag is still moderate, and the gearing puts it near its efficient operating range.

Above roughly 60mph aerodynamic drag becomes the dominant force, and because it increases with the square of speed, the fuel required climbs steeply. This is why the same car will return very different figures at 60, 70 and 80mph.

In practical terms, on a long motorway run, sitting at 60 to 65mph rather than 70 costs a few minutes an hour and returns a noticeable improvement in economy. On a two hour drive that is a small time penalty for a meaningful saving.

The reverse is also true at the bottom end. Crawling in heavy traffic in first and second gear is very inefficient, which is why urban economy figures are always the worst on the label.

Gear changes and engine speed

Changing up earlier keeps engine speed and internal friction down. The DVSA's own eco driving guidance is to change up before around 2,500rpm in a petrol car and around 2,000rpm in a diesel.

• Skip gears where it makes sense. Going straight from third to fifth on a gentle road is fine if the engine is not labouring.
• Use the highest gear that pulls cleanly. If the car shudders or the engine drones, you are too high.
• In an automatic, ease off the accelerator slightly once you reach your target speed. It prompts the box to shift up rather than holding a lower gear.
• Ignore the temptation to hold gears for engine braking on the flat. In gear on a trailing throttle the fuel is already cut.

Does idling waste fuel?

An idling engine returns zero miles per gallon, so any stationary time with the engine running is pure waste. As a rule of thumb, if you expect to be stopped for more than a minute, switch off.

• Stop start systems do this automatically and are worth leaving switched on. They are designed for it, with an uprated starter and battery.
• Warming the car up on the drive is unnecessary on any modern engine. It warms up far faster when driven gently, and leaving a car unattended with the engine running on a public road is an offence as well as an invitation to a thief.
• Idling on a public road unnecessarily can attract a fixed penalty notice from the local authority.
• Level crossings, drive throughs and school gates are the common culprits. Switching off also stops you pumping exhaust into the space where people are standing.

Tyre pressures and maintenance

Tyres are the cheapest economy improvement available, and the most neglected.

• Check pressures monthly, cold. Use the figure on the door shut, fuel flap or in the handbook, not the maximum moulded into the sidewall. Under inflated tyres flex more, generate heat, wear out at the edges and increase rolling resistance directly.
• Check when loaded. Most cars have a higher recommended pressure for a full load or motorway cruising. It is printed alongside the normal figure.
• Buy sensible tyres. The EU style tyre label shows a fuel efficiency rating from A to E. The difference between the extremes over the life of a set of tyres is not trivial.
• Alignment. A car pulling to one side or wearing one edge of a tyre is scrubbing energy away constantly. It is a cheap fix.
• Servicing. A clogged air filter restricts airflow, old oil increases internal friction and worn spark plugs cause incomplete combustion. None of these are dramatic on their own and together they add up.
• Sticking brakes. A binding caliper drags constantly. If a wheel is noticeably hotter than the others after a drive, get it looked at.
• Warning lights. An engine management light often means the car has dropped into a fallback mode that ignores efficiency entirely.

Weight, roof bars and aerodynamics

Weight matters most in stop start driving, where you accelerate repeatedly. Drag matters most at speed.

• Empty the boot. Tools, pushchairs, bags of sand and gym kit that lives in the car permanently all cost fuel every mile.
• Take roof bars and roof boxes off when not in use. This is the biggest aerodynamic penalty most drivers add to their own car. An empty roof rack left on all year is a permanent tax on every motorway journey.
• Close the windows above about 40mph. Open windows disrupt airflow along the side of the car and create real drag.
• Do not carry half a tank of fuel to save weight. The saving is negligible and running low risks picking up sediment and stressing the fuel pump.
• Check under the car. Plastic undertrays, wheel arch liners and front spoilers are there for aerodynamics, not decoration. A missing or hanging undertray after a kerb strike or a pothole increases drag and lets water into places it should not go. If yours is loose or gone, it is worth putting right.
• Damaged bodywork counts too. A bumper hanging proud after a car park knock, a missing grille section or a bonnet that no longer sits flush all disturb airflow. Most of this is repairable without a full respray.

Air conditioning: on or off?

Air conditioning uses fuel, but so does driving around with the windows down. The right answer depends on speed.

• Below about 40mph, open windows are usually the more economical choice. Drag at low speed is small and the compressor load is not.
• Above about 40mph, close the windows and use the air conditioning. Drag is now the bigger penalty.
• Park in the shade in summer so the system has less work to do when you get back in, and open the doors for a moment to dump the hot air before setting off.
• Run it occasionally in winter. The system circulates lubricant with the refrigerant, and letting it sit unused all winter leads to seals drying out and leaks. It also demists the windscreen far faster than heat alone.
• Turn off recirculation once the cabin is comfortable, or the glass fogs up.

Short journeys, cold starts and diesel particulate filters

A cold engine is the least efficient it will ever be. Fuel is enriched to get combustion stable, the oil is thick, the catalytic converter is not yet at working temperature and internal friction is high.

• The first mile or two of any journey uses considerably more fuel per mile than the rest of it.
• Combining several short errands into one trip means only one cold start rather than four.
• Walking or cycling for genuinely short trips avoids the least efficient driving there is.
• Diesel cars need regular longer runs. The diesel particulate filter needs a sustained period at temperature to burn off accumulated soot. A diesel used only for short urban journeys will eventually block its filter, which is an expensive fault and one that wrecks economy in the meantime. If your driving is all short trips, a petrol or hybrid car suits you better.

Which fuel should you use?

For most drivers, standard E10 petrol or standard diesel is the right choice. Paying more for super unleaded only makes sense in specific cases.

• E10 is the standard 95 octane UK petrol and contains up to 10 per cent ethanol. Ethanol carries less energy per litre than petrol, so economy is marginally lower than with E5, but E10 is cheaper and the difference is small.
• E5 super unleaded is higher octane with up to 5 per cent ethanol. It benefits engines that specifically require higher octane, typically performance and some turbocharged engines whose handbook states a minimum. In an ordinary family car it will not deliver a saving that covers the price difference.
• E10 compatibility. Almost all petrol cars built since 2011 are compatible. Some older and classic vehicles are not, because ethanol attacks certain rubber and fibreglass components. The government publishes a compatibility checker, and affected cars should use E5.
• Diesel in the UK contains up to 7 per cent biodiesel. Premium diesels carry extra detergent and cetane improvers, which can help a high mileage engine keep its injectors clean but will not transform economy.
• Where you buy matters more than the grade. Motorway service areas are consistently the most expensive place to fill up, and planning a fill before you join the motorway is worth more than any additive.

Route planning and journey timing

The cheapest mile is one you never drive, and the second cheapest is one at a steady speed.

• Avoid congestion rather than distance. A slightly longer route that flows is usually cheaper than a shorter one full of junctions and queues. A navigation app with live traffic pays for itself.
• Travel outside peak times where you can. Sitting in the Manchester rush hour burns fuel to travel almost nowhere.
• Combine trips so the engine only warms up once.
• Reverse into the drive so you leave forwards. Manoeuvring a cold engine at full choke enrichment is expensive, and it is safer to leave nose out.
• Do not circle looking for a closer parking space. Take the first available one and walk.

Do fuel saving gadgets work?

No, with one narrow exception. Fuel line magnets, intake vortex generators, ionisers and plug in chips promising large gains do not deliver repeatable improvements, and several have attracted advertising rulings over their claims.

The narrow exception is fuel system detergent. If an engine genuinely has fouled injectors, causing rough running and poor economy, a proper detergent additive or a few tanks of a high detergent fuel can restore performance. That is fixing a fault, not improving a healthy engine.

Simple aerodynamic modifications such as grille blanking are also usually a waste of effort on a modern car, which already has active grille shutters and a designed cooling path. Interfering with it risks overheating.

How to measure your real fuel consumption

You cannot manage what you do not measure, and the trip computer is not a reliable measurement.

Do a brim to brim calculation. Fill the tank until the pump clicks off, reset the trip meter, drive normally, then fill again at the same pump to the same click. Divide the miles travelled by the litres added, then multiply by 4.546 to get miles per gallon, since UK fuel is sold in litres but economy is quoted in imperial gallons.

Do that over three or four tanks and you will have a real baseline. Trip computers are typically optimistic by a few per cent, but they are useful for comparing one journey with another, which is the point.

Track it against changes. Take the roof bars off for a month and see what happens. Sit at 60 rather than 70 for a few motorway runs. The numbers make the habits stick in a way that advice does not.

The costs around fuel

Fuel is only part of what a car costs to run, and in the UK several other charges are tied to how much it emits.

• Vehicle excise duty is based on CO2 emissions for cars registered from April 2017 in the first year, then a standard rate, with a supplement for cars over a certain list price. Choosing a lower emitting car reduces the first year bill considerably.
• Company car tax is calculated on a percentage of list price set by CO2 emissions, which is why plug in hybrids and electric cars are so heavily favoured by company drivers.
• Clean air and low emission zones charge older, higher emitting vehicles to enter certain city centres. Check the rules for anywhere you drive regularly.
• Insurance and tyres are unaffected by driving style in the short term, but smooth driving that saves fuel also saves brakes, tyres, clutches and bodywork.

Cutting fuel use without changing your car

If you want a larger reduction than driving technique alone can deliver, the options are about using the car less rather than differently.

• Share the journey. Two people in one car halves the fuel per person. Workplace car share schemes and apps make matching straightforward.
• Use public transport for the routes it suits. Commuter rail and tram journeys into Manchester avoid both fuel and parking.
• Walk or cycle short trips. Under two miles, the car is at its least efficient and often no faster door to door.
• Consider a hybrid for urban driving. Regenerative braking recovers energy that would otherwise become heat, which is exactly what stop start town driving wastes.
• Consider an electric car if your mileage and charging suit it. The efficiency advantage is largest in the conditions that hurt petrol and diesel cars most.