Top 5 fuel economy myths

Published Date: 11th May 2017

It is well known that mileage per gallon of fuel can be improved through conservative driving practices, following the proper service schedules and tire maintenance. However there are different mpg theories scattered around the internet and rumours that you may have heard from a friend of a friend that used to be a mechanic. But many of them are from days of old and don’t affect the modern car or engine the same way.

Opening you windows will increase fuel consumption?

With air conditioning available as standard across a broad range of manufacturers these days, maybe try to open your windows and save a bit fuel instead of running the a/c, but a common misconception is that this will lead to extra drag and more fuel being used also.

A picture of the air conditioning controls inside the car

The real answer is that although a/c compressors on new car engines have come a long way in terms of efficiency they still can reduce your mpg figure by 2-4 miles depending on the cabin size. Compare that with opening your windows that will create that little extra drag resulting in very minimal fuel usage compared with the a/c on.

Warm up your car before setting off?

The common thinking behind this has us all believe this will reduce engine wear and the car will be more fuel efficient when you do eventually set off. The engine wear part is now a myth, on the modern car as this was true in the days before your electronically controlled fuel injectors and advanced fully synthetic oils that all work together along with other systems, to quickly get the engine up to operating temperature making cold start engine wear a thing of the past.

Large truck spitting flames out of the exhaust

 The other bit is true, engines are much more fuel efficient at peak operating temperatures compared to being cold. However the fuel used idling the car up to temperature is wasted on just that, it’s much quicker and fuel efficient to drive your car up to temperature and also creates less pollution.

Low rolling resistance tyres are the best?

This one is correct, when it comes down to the mpg of a car the tyres are estimated to make up around 20% of the total in rolling resistance. A recent study from the University of Michigan in the USA proved that you can gain as much as 1-2 mpg from having the tyres fitted. With that said they still advise to go for the tyre with the best all round attributes like good all weather performance and wear before thinking about fuel economy.

A selections of tyres all stood up with their tread pattern visible

You can make up the difference in mpg by using better driving techniques such as avoiding harsh acceleration and braking, another tip would be to keep on top of your tyre pressure and have them set at the recommended levels usually found on the B post, door shut or fuel flap for optimum mpg.

Old or dirty air filters?

In the case of dirty air filters, this is another fact but only applies to the cars of old again that would be subject to poor emissions and mpg caused by the poor airflow affecting the fuel/air mixture in the cylinder.

Now new cars don’t suffer with the same symptoms as the air going into a cylinder is constantly monitored by an airflow sensor and then the fuel is carefully adjusted to match. The only downside to this would be a reduction in performance that comes when starving an engine of oxygen/air.

Engine bay with a nice clean air filter

Cheap versus Premium fuel

At most fuel stations across the UK you now have the option of buying a premium fuel, with claims to deliver better performance, mpg and a cleaner engine. So does it ring true? And is it worth the extra 10,11 or 12p per litre?

The super or premium fuels generally have a higher octane rating, the rating is a number given to the fuel to measure the amount of compression it can take before igniting, so the higher the number the more pressure it can withstand. This type of fuel is generally better for turbocharged or supercharged engines with a higher compression ratio, as the fuel will deliver more power when compressed in the cylinder and will not cause any knocking due to pre detonation.

Fuel pump selection of premium and regular fuels

These fuels also have double the amount of detergents and additives that will help to give the engine a deeper clean, protect against corrosion and engine wear for better performance. The cheap supermarket fuel is by no means inferior as they all have to follow strict  

The higher octane rating in theory should help the engine burn more efficiently and provide more power for less fuel used. Most reports have found only a small increase in fuel efficiency and therefore not really worth the extra ten pence a litre more in terms of mpg but it’s able to deliver extra power to the wheels if you own a performance car.