Does Leaving the Engine Running (Idling) Damage Your Car?

Does Leaving the Engine Running (Idling) Damage Your Car?

We’ve all been there—waiting for someone in the car, tempted to leave the engine running to keep the AC on or the radio playing. Or maybe you’re a delivery driver who leaves the car idling as you drop off packages.

But have you ever wondered if idling is actually harming your vehicle? Many of us grew up hearing mixed messages about whether it’s better to leave the engine running or switch it off. Let’s clear up the confusion once and for all. In this blog, we’ll dive into the myths and facts about idling, and find out if it really does any damage to your car.

5 Car Idling Myths Debunked

Myth 1: Idling Is More Fuel Efficient

Contrary to popular belief, idling is not more fuel efficient than turning your engine off and on again. In fact, idling actually uses more fuel. This is especially important for vehicle-fleet operators, where fuel is a major expense, making up about 20 per cent of total operational costs.

The amount of fuel consumed while idling depends on several factors like your vehicle’s weight, engine size, and the type of fuel it uses. However, two things are certain: idling burns more fuel and makes you refuel more often.

A report by Transport Energy/Emission Research (TER) found that idling for more than 10 seconds uses more fuel than restarting your engine. While it might not seem like a big deal on a small scale, the impact is significant when you consider all the fleet vehicles across Australia. For example, an idling diesel truck can burn up to 3.78 litres of fuel per hour. Eliminating unnecessary idling can lead to massive savings. And, it’s better for the environment.

Myth 2: Idling Doesn’t Cause Much Wear & Tear

You might have heard that letting your car idle doesn’t cause any harm, but the reality is a bit more nuanced. While short periods of idling won’t instantly damage your vehicle, frequent and prolonged idling can lead to some long-term issues.

  • Idling can cause twice the wear on your car’s internal parts compared to driving at regular speeds. When your car idles, the engine runs at a low speed, which can cause incomplete combustion. This means that residue can build up on parts like spark plugs and cylinders. Over time, this build-up can reduce your engine’s efficiency and cause damage.
  • Idling can lead to unburned fuel mixing with the engine oil, which makes the oil less effective at lubricating engine parts. This contaminated oil can increase wear on your engine and mean more frequent oil changes .
  • If you drive a diesel vehicle, idling can be especially problematic. It can cause the exhaust temperature to drop below the level needed for the diesel particulate filter (DPF) to work properly, leading to soot build-up and potential filter clogs .
  • Idling also puts extra strain on your car’s battery and alternator. While the alternator does charge the battery during idling, it’s less effective than when you’re driving, especially if other electrical systems are running .

In short, while a bit of idling here and there won’t ruin your car, it’s best to avoid long periods of idling whenever possible to keep your vehicle in good shape and save on maintenance costs.

Myth 3: It’s Illegal to Idle Your Car in Australia


It’s not actually against the law to idle your car in Australia. However, there are some rules you should be aware of.

Leaving Your Car Unattended: In states like New South Wales, Queensland, and Victoria, it’s illegal to leave your vehicle unattended and unlocked if you’re more than three metres away from it, regardless of whether the engine is running. So, if you step away from your car and leave it idling, you could be fined. For example, in New South Wales, you can get a $114 fine for this, and $117 in Victoria.

Environmental Impact: While there isn’t a specific anti-idling law, many local councils encourage drivers to reduce idling to cut down on air pollution. Idling wastes fuel and releases unnecessary emissions, which isn’t great for the environment. By turning off your engine when you’re stopped for a while, you can save fuel and help reduce pollution.

Exceptions: There are some exceptions to these rules. For instance, certain vehicles like refrigerated trucks need to idle to keep their goods cool. Also, in extreme weather, you might need to keep your engine running for heating or cooling, but these cases are usually specific and regulated.

The best thing to do is turn off your engine if you’re going to be parked for more than a minute. Modern cars are designed to handle frequent restarts, so turning off your engine saves fuel and cuts down on emissions without harming your car.

Myth 4: Idling is Good for the Battery and Alternator

Some drivers think that letting their car idle is good for the battery and alternator, but that’s not really the case. Sure, when your car is idling, the alternator is charging the battery. However, modern cars are built to keep the battery charged just by driving normally. So, if you’re idling to keep your battery in shape, it’s time to rethink. Normal driving is perfectly fine to keep your battery charged and your alternator healthy.

Myth 5: Warming Up Your Car by Idling is Necessary

A lot of people think they need to let their car idle for a few minutes to warm up the engine, especially on cold mornings. But guess what? Modern cars don’t need that extra time to get going.

Today’s engines are designed to be efficient right from the start. Idling your car to warm it up isn’t just unnecessary, it’s also less effective. When you drive your car, the engine heats up faster because it’s working harder than it would be just sitting there idling. This means your car reaches its optimal temperature more quickly when you start driving, which helps reduce fuel consumption and emissions .

So, next time you’re tempted to let your car sit and idle to warm up, remember: the best way to warm up your engine is to simply start driving.

Car Idling FAQs

Can I leave my car running idle?

Yes, you can leave your car running idle, but it’s generally not a good idea. Idling wastes fuel, increases emissions, and can cause unnecessary wear on your engine. It’s usually better to turn off the engine if you’re going to be stationary for more than a minute or two.

What damage can idling cause?

Idling for long periods can cause several issues like engine wear and tear, fuel contamination, battery & alternator strain and increased emissions.

Is it bad to let your car idle for 15 minutes?

Yes, it’s generally bad to let your car idle for 15 minutes. This extended idling wastes fuel, increases emissions, and can cause engine wear over time. Modern engines don’t need to idle to warm up; they warm up faster and more efficiently when you start driving.