The Truths and Myths About How to Optimize Your Car’s Fuel

Across the UK, rising fuel prices are straining household finances. With energy costs, supermarket prices and council tax increases already increasing the pressure, the latest skyrocketing increases in petrol and diesel have left many already struggling families wondering how they will meet their monthly bills.

Last week the average cost of a full tank of petrol for a typical 55-litre family car topped £100 for the first time, according to figures from data firm Experian Catalist. The average price of a liter of petrol on UK forecourts hit a record 182.3p on Wednesday and the average price of a liter of diesel on Wednesday was a record 188.1p.

Read more:How much does petrol and diesel cost in other countries in Europe compared to the UK

But with so much conflicting advice floating around, it can be hard to separate fact from fiction when it comes to the best ways to save on your fuel costs. So we’ve rounded up some of the best tips from the RAC’s online car magazine, Energy Saving Trust,, and many more to give you the best possible chance of saving money on fuel. We’ve also highlighted some of the most commonly cited myths and explained which ones to consider and which ones to ignore.

Drive Efficiently by Preparing

One of the most basic tips for efficient driving, and cited by almost every automotive expert, is to shift gears as soon as you can rather than constantly relying on your right foot on the accelerator. That’s because, of all things, excessive speed is often cited as the most fuel-intensive factor. Driving at high rpm increases fuel consumption. Therefore, when accelerating early, shift into the highest gear possible for your car while staying within the speed limit.

This applies to all driving – things like rapid braking, sudden acceleration and deceleration, and harsh use of the steering, as well as other characteristics of driving style, are all likely to have impact on fuel consumption. Ideally, it’s best to think ahead, drive smoothly, and rely on the gears to get the job done as much as possible, only accelerating when needed.

Tire pressure

An often overlooked way to save money is to make sure your tire pressure is correct. Under-inflated tires increase your vehicle’s drag, which increases fuel consumption. A study by the National Highway Traffic Safety Administration (NHTSA) in the United States found that every 1% drop in tire pressure was correlated with a 0.3% reduction in fuel consumption. This means that a tire under-inflation of 10% increases fuel consumption by 2%. At 20% underinflation, fuel consumption increases by 4%.

Looking at these numbers, the impact of tire pressure on your costs is clear, so make sure your tires are inflated to the correct pressure. This should be in your owner’s manual, on the driver’s door sill, or inside the fuel filler door.

Do not use your air conditioning or heating unless you really need it

Yes, we know how tempting it is on a cold winter morning to crank the heat to high on your commute. Also, how many times have you turned up the air conditioning while driving on a summer day?

But if you want to save fuel, it might be worth avoiding it unless you really need it. Running the car heater uses engine power and therefore increases fuel consumption. This applies to both heating and cooling. Even though it sounds silly, it’s best to dress appropriately if you’re really trying to save fuel.

Don’t be weighed down by things you don’t need

Although they are convenient for traveling abroad, keeping roof boxes and racks above your car creates wind resistance and makes your car burn more fuel due to the “drag” effect. This is increased as you drive faster. According to the Energy Saving Trust, an empty roof rack adds 16% drag when driving at 75 mph. At equal speed a roof box adds 39%, making your vehicle much less fuel efficient. It might sound funny, but the same effect (although much less so) happens even with the little flags you attach to the side of your car.

Unsurprisingly, this also applies to those of you who like to use your car trunk as an informal storage space. While this is unlikely to make a huge difference to your fuel costs, it stands to reason that refueling your car does make it heavier, which will result in slightly higher fuel consumption. So put those boxes that are in the trunk in the attic if you can.

Combine trips

The temperature of your engine will also have an impact on fuel consumption. A cold engine is likely to consume more fuel than when it has warmed up, even though the mileage may be the same. So if you’re planning your day, it might be worth considering how many things you can pack in one trip rather than repeatedly turning the car off and on again. This can help you save fuel, although with school trips, commuting, errands and after-school activities this is obviously not always possible.

Should you drive with less fuel in your tank?

An oft-touted solution is that you should drive on less fuel because it means you’re carrying less weight. It’s delicate. On the one hand, the opinion of many experts – that a fully filled tank is heavier to drive and will therefore affect efficiency – seems logical given our previous advice on weight. But others say your gas tank, when full, is less than 5% of your car’s total weight. Reducing the weight of your car by 2.5% by only half filling your tank is therefore unlikely to have a noticeable effect on your fuel consumption.

The advice here is that if you fill your tank half or full, it’s unlikely to have a major impact on your mileage – if it does, it’s likely to be pennies. This is especially true when taking into account the extra trips to the gas station that would be required by refueling less.

Should I empty my fuel tank before refueling?

This one seems to be a bit clearer. Most experts agree that you should avoid regularly riding empty or nearly empty, as this creates a number of risks. In addition to the obvious risk of running out of fuel in the middle of the road, driving with very low fuel levels could also damage your car.

As the fuel level drops, the car begins to pick up debris from the bottom of the tank, which can damage both the fuel filter and the pump. The catalytic converter could also be damaged. If you run out of gas, the fuel pump can go dry, which could cost you a hefty garage bill. Generally speaking, it’s ideal not to let your gauge drop below a quarter tank, according to several experts.

How far can you go when the fuel gauge hits zero?

How far you can go after your fuel light comes on depends on your car. For example, according to, you normally have around 42 miles left in a Ford Focus but only 30 in an Audi TT.

Likewise, once the fuel gauge reaches zero, the distance you can travel depends on the car. Typically it’s about an extra 10-20 miles but that’s not certain and best avoided if you don’t want the car to stop in the middle of the road and possibly cause Other problems. So the good news is that you’re not going to cut the minute you hit zero – but it’s best to avoid it anyway.

What is the optimal fuel-efficient speed for driving?

This is another common myth. Generally speaking, there is no optimum driving speed for fuel economy. Over the years, 56 mph has often been considered the optimal speed. As RAC explains, this was because the old fuel economy test was run at three speeds: urban, 56 mph and 75 mph – and 56 mph was still the most efficient of these. Generally cars are most efficient at 45-50 mph, but there are many other factors such as the ones above that collectively impact fuel efficiency, so it’s not really applicable in self.

Should I fill up in the morning?

It is sometimes said that refueling your car in the morning or late at night will give you more fuel for your money because gasoline or diesel will be denser when cold. While this is true in theory, in most cases the fuel you get when you go to a station is stored in large underground tanks that keep the fuel temperature under control. This means that the fuel you buy will be at roughly the same temperature throughout the day and night. Even fuel coming directly from tankers, as we saw a few months ago when shortages hit the UK, is temperature controlled. The gas becomes more volatile when it is hot, so large tankers are also insulated. Therefore, don’t focus too much on refueling in the morning or evening – whenever you need fuel, that’s the best time to do it.

Should I keep my tank half full to prevent fuel evaporation?

Again, this one is unlikely to make much of a difference. It is sometimes said that the more fuel you have in your tank, the less air will fill its empty space, which means there is less chance of your gasoline evaporating. According to even in a nearly empty gas tank the liquid to vapor ratio is stable and no gas really disappears. Studies have shown that even if this were true, your money savings would be negligible.

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