Mythbusters: Does winter really drain your fuel tank?

Separating fact from fiction isn't always easy in the motoring world and that has opened the door to plenty of myth-making.

Premium fuel cleans your engine. Automatics use more fuel than manuals. A car needs a long drive to clear the engine. No doubt you can think of a few yourself.

So what about this one: cars use more fuel in the winter months. True or false? Whether you drive a petrol or diesel vehicle, we put the myths to the test to help you drive smarter in the final weeks of winter.

Cold weather and fuel economy – the basic truth

Unlike some motoring myths, this stacks up. The 2014 study The influence of street environments on fuel efficiency: insights from naturalistic driving¹ included weather in its list of major factors that influenced fuel efficiency and concluded that it did indeed deteriorate when temperatures dropped.

Australian data tells the same story closer to home: a Bureau of Infrastructure, Transport and Regional Economics² study of real-world driving found that lower ambient temperatures and wet weather consistently push fuel consumption higher – even within the modest seasonal swings most of us experience.⁠

Why? Well, there are myths that attempt to explain this too.

Does cold weather lower your tyre pressure and cost you fuel?

If you know your science, you'll know cold air is denser than warm air and is why tyres lose pressure when the temperature drops. Another physical truth – that rolling resistance increases as tyre pressure drops – means this phenomenon has a negative impact on your fuel economy.

With tyre maker Continental

estimating the loss at 1-2 PSI for every 10ºC, tyres that are correctly inflated in summer can be well under pressure by winter. And while true winter tyres (also known as snow tyres) aren’t widely used in most of Australia, maintaining correct pressure all year round is still critical for safe handling.

If unsure of your vehicle’s current tyre pressure, you can stop at your local Shell and check your tyre pressure.

Is the heater as draining as AC?

While using the heater does technically increase fuel consumption, you won't notice it and it won't be as significant as using AC.

That's because a car's heater essentially recycles heat generated by the engine. The main energy consumer is the fan used to circulate the air, and those extra few amps only slightly increase the load on the alternator and engine itself.

Using AC, in contrast, engages a compressor that causes significant drag on an engine, making it work measurably harder and use more fuel.

How much? There's no simple answer because every car is different but five to 10 per cent is a common estimate, with the systems in older cars typically less efficient.

Car seat warmers draw power, but do they waste fuel?

Just like the heater, heated seats do consume electricity and technically increase fuel consumption.

Again, though, the total power draw is typically a few miniscule amps, it is not something you'll notice ‘at the pump’.

Does cold air make your car work harder to cut through it?

As well as dropping tyre pressures, the increased density of cold air does make it harder for a car to move through it, meaning more engine power is needed to overcome the increase in aerodynamic drag.

Just how much this phenomenon actually impacts fuel economy has not been studied but the science stacks up, especially at higher speeds when drag is at its greatest.

Should you warm up your car? Not anymore

Back when cars used a carburettor (a mechanical device that mixed air and fuel before sending it to the engine) to feed fuel into the engine, this was indeed correct – your engine did need to be warm before it performed smoothly and efficiently, making a winter warm-up routine useful.

But today's computer-controlled fuel injection technology can alter the air/fuel ratio and myriad other factors with microsecond precision, allowing an engine to warm up much quicker and without any of the driveability issues of old.

How to save fuel during the end of winter and beyond

• Check your tyre pressures regularly and keep them inflated to specification – look to your car's owner manual for guidance. Your local Shell service station has air pumps available year-round, making it easy to top up, especially during winter.
• Avoid winter idling unless you need the heater to clear foggy windows.
• Remove unused roof-mounted equipment to minimise aerodynamic drag, especially if you drive a lot on the highway.

¹ _{Wang, X., Liu, C., Kostyniuk, L. P., Bao, S., & LeBlanc, D. J. (2014). The influence of street environments on fuel efficiency: Insights from naturalistic driving. International Journal of Environmental Science and Technology, 11(8), 2291–2306. https://doi.org/10.1007/s13762-014-0584-1}

² _{Bureau of Infrastructure, Transport and Regional Economics (BITRE) 2017, Fuel economy of Australian passenger vehicles — a regional perspective, Information Sheet 91, BITRE, Canberra.}

_Disclaimer
^{Viva Energy Australia Pty Ltd (“Viva Energy”) has compiled the above article for your general information and to use as a general reference. Whilst all reasonable care has been taken by Viva Energy in compiling this article, Viva Energy does not warrant or represent that the information in the article is free from errors or omissions or is suitable for your intended use.}