How often should I drive my car?

Many of us have changed how we use our cars since COVID-19. More of us now work from home and get deliveries to our home, and plenty of us now realise our cars have been sitting around for weeks or even months without being driven. Does this do any harm?

The short answer is yes. Cars are built to be used and problems arise if they’re left standing idle for long periods of time untouched. Broadly speaking, there are five areas that will be affected if a car is left unused for an extended time: the battery, the powertrain, the brakes, the tyres and the bodywork/electrics.

And just because you don’t use your car, be sure to stick to its service routine. Many fluids need to be changed at set time (not just distance) intervals because they simply degrade over time – even if the car is rarely used. Think of it as you would milk: nobody drinks ‘fresh’ milk that’s been left in the fridge for a month.

The first problem you’re likely to notice with your under-utilised car is that its battery loses voltage and does not have enough power in it to start the car. Various computers in modern cars still draw a small amount of current, even when the vehicle is ‘asleep’.

A car battery is a bit like a dripping tap: it ‘leaks’ current out of it very slowly even if you don’t use the car. After a period of sitting without any charge being added to it, the battery’s capacity will drop to a point where it will not be able to provide the starter motor enough power to engage and start the engine.

Leaving your car’s battery fully discharged will shorten its life, so it’s important to keep it charged – either via the alternator when it’s being driven, a trickle-charger or, better still, a battery conditioner like those offered by CTEK.

Meantime, the oil that provides a protective coating on internal components of the powertrain – in particular the engine – will eventually drain from bearing surfaces and the oil will break down over time as well, therefore making it less capable of offering protection.

This is especially the case if the car only does short trips in between long periods of standing around as such trips will leave more moisture in the oil, which is normally burnt off when the engine gets nice and hot after an hour or more of driving.

A modern diesel, if only used for irregular short trips, will have its own problems. Eventually it will get a blocked diesel particular filter (DPF), which can cause breakdowns and expensive repairs. A regular highway run is important for these vehicles.

Brake fluid also won’t last forever (many car-makers recommend replacement every two years) and will degrade over time as it eventually gets moisture in it, which will corrode the brake calliper pistons, while rubber seals can dry out and fail due to lack of use.

Then there’s the cooling, transmission, suspension, power steering and air conditioning systems that don’t generally do well if left to sit a long while. Like the brakes, the rubber seals in all these systems can dry out without use over time, which can cause the component to fail, leak or both.

Petrol (or diesel) fuel also does not last forever. Although many cars have plastic fuel tanks these days, preventing rust due to moisture entering the tank, the fuel itself will break down over time and eventually ‘go off’. If left in the summer heat, BP says petrol can last as little as three months before it does so, and the result will be the car won’t run very well.

Tyres also degrade over time and usually become unserviceable after about seven years if left out in UV light conditions. Before that, they can develop ‘flat spots’ if left on a stationary vehicle for too long, especially if under-inflated.

A car’s body and electrics can also suffer from lack of use, particularly if the vehicle is left out in the elements. Left unchecked, leaves can quickly block drainage points and trap water, causing corrosion or allowing moisture water to enter and damage the interior.

Rodents can chew into wiring or seats, resulting in expensive repair bills. Bird or bat excrement eats into paint very easily and quickly, doing not only cosmetic damage but also increasing the chances of corrosion.

There is no minimum prescribed period for driving or at least starting your car, but the longer you leave it the more likely bad things will start to happen. If you drive your car every two weeks for at least 30 minutes each time, you are unlikely to have problems due to lack of use.

If your car is driven less frequently or only used for short trips, it will put a lot of strain on the battery. The best way around this is to charge the battery regularly at home to keep it in good condition. A flat battery is not only an inconvenience, it also damages the battery and shortens its useful life.

You can either use a smart trickle charger connected to the battery while the car is parked (which is good idea anyway, to allow the battery to keep up its voltage and to condition the battery fluid) or make sure you drive the car every three to four weeks. Allowing a car to idle for 10 minutes will probably get the engine up to normal operating temperature, but won’t charge the battery much – if at all. Preferably drive the car for at least half an hour.

If you are going away for six months and you don’t want to sell your car (and have a secure, dry place to store it) then you may choose to lay it up properly. That’s a more complicated process involving replacing all fluids, draining fuel out of the tank and lifting the vehicle off its tyres, then reversing all that when you return.

While an electric vehicle isn’t quite as sensitive to infrequent use as a combustion-powered vehicle in order to stay in top shape, there are still some things you need to pay attention to. EVs still have brake fluid and tyres, so the same conditions apply.

An EV battery pack will usually cope fine with standing around without being recharged for a couple of months. Check with the manufacturer, but if an EV is left ‘idle’ for six months or more – especially in summer heat – it can degrade the battery pack and end up doing permanent damage to it, depending on the state of charge when you leave it and the battery capacity itself.

Related reading:
- Which Australian states offer the best EV incentives?
- Should you buy a car more than 10 years old?
- Five questions to ask before buying a car