Is it okay to leave the engine running?

Race car drivers – and bank robbers, if we’re taking into account less legitimate ways to make large amounts of cash in a relatively short period of time – know that keeping the engine going is a crucial part of achieving the best results for the job at hand.

Delivery drivers may also hold the opinion that keeping the engine idling is the most efficient way to get things done, since stops are usually brief – but is it really the smartest way to go about things?

If you’re a serial idler, here’s a few important things to keep in mind while the motor is ticking over…

First, let’s dispel a popular myth: idling is not more efficient than turning the engine off and on again, and doing so doesn’t use less fuel. Besides paying wages, fuel is the biggest cost for vehicle-fleet operators, typically accounting for 20 per cent of a fleet’s total operational costs.

A recent Transport Energy/Emission Research (TER) report found that Australians are likely to leave their engines idling 20 per cent of the time in normal traffic conditions. Considering there are more than 20 million motor vehicles in Australia, that’s a lot of fuel being burned for no good reason.

Weight, engine size, and the type of fuel your vehicle takes all factor into how much is being consumed while an engine idles.

Regardless, there are two unavoidable truths: idling will burn more fuel, and subsequently require you to refuel more often. By turning your engine off rather than leaving it idling, you can reduce fuel costs by 10 per cent or more (the TER report also found that idling your vehicle for more than 10 seconds uses more fuel than switching the engine off and on again).

It may not seem like a big deal, but when taking into account all of the fleet vehicles in Australia, the yearly savings from eliminating idling would be huge – especially since an idling diesel truck can burn a whopping 3.78 litres of fuel per hour.

There are a few more myths to address, so here are the facts. Firstly, turning the engine off and on again does not cause strain on the electric motor; secondly, idling a vehicle does waste fuel and creates additional gas emissions that are unnecessary; and finally excessive idling can damage your engine's components, including the exhaust systems, spark plugs and cylinders. Did you know idling can actually cause twice the wear on internal parts compared to driving at regular speeds?

Damage to the engine and exhaust system is possible, however, especially when ‘low idling’, which is when the engine revs are in the 600-750 rpm range. Low idling can produce sulphuric acid, which is as nasty as it sounds; eating away at the engine and other exhaust-system components.

If you’re driving a diesel vehicle, other issues can arise. While low idling, the diesel exhaust temperature can drop below 250 degrees, which is the temperature that a diesel particulate filter (DPF) needs to operate at. Below that? You’re risking clogging up the DPF with soot. Engine oil also takes a hit while idling: the oil can also become contaminated with soot and acid, which, as you’d expect, means the oil won’t last particularly long. The upshot? Greater vehicle maintenance costs, and a shorter life span for the engine.

While there’s no anti-idling legislation in Australia, there is a particular law to be aware of if you’re a driver who leaves your vehicle unlocked and unattended while on the job.

In New South Wales, Queensland and Victoria it’s illegal to leave your vehicle unattended and unlocked if you venture more than three metres away from it, regardless of if the engine is running or not. Expect to receive a fine if you get caught: in New South Wales, for example, you’ll get hit with a $114 on-the-spot fine for venturing more than three metres away from an unattended, unsecured vehicle.

^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.}