Car Advice

Don’t bother to warm up your car

03 Jan 2018

Isaac Bober 8

There’s a belief out there that, particularly on a cold day, you’ve got to warm up your car for several minutes before heading off. You don’t.

WHEN I GOT MY first car my old man used to tell me I had to warm it up before heading off in it, particularly on cold winter’s days. Indeed, he often used to head out during winter, start up his work van and leave it idling while he came back inside for a cup of coffee. A smart guy, the old man swore by this process for years … he must have tipped thousands of dollars down the drain in burnt fuel. And he didn’t even leave the house. See, it was a hangover from when he owned an old Falcon with carburettors, that car you did need to warm up.

He’s seen the light now, however, and he no longer warms-up his car. And neither should you. See, cars don’t need to be idled to warm up, not even in winter. An older, classic car with carburettors instead of fuel injection might need a minute or two to let the oil thin out, but leaving it idle for five or more minutes could cause damage to the engine by allowing the oil to mix with too much fuel and thus become too diluted.

So, why don’t you need to warm up your car? Simple. Just about every modern car, indeed almost every car built since from the 1990s onwards will have electronic fuel injection. That means there’s a clever little device attached to your engine that tells the fuel injectors to stay open a touch longer, to allow in more fuel, to help the engine run when cold. Because you’ve got more fuel than normal flowing into the engine when it’s cold, sitting and letting it idle for more than the briefest of moments is a complete waste of fuel.

This means that as long as your car fires up first go there’s no need to sit and idle the thing, you can just grab a gear and go. Basically, the first few minutes of your drive are your car’s warm-up period, so don’t go flooring the thing from the get-go. Indeed, modern engines will warm up quicker when they’re driving than when they’re sat stationary, so…

Idling wastes fuel, that’s a fact, and that’s why so many car makers are fitting their cars with stop/start which turns off the engine when the car comes to a stop, say, at a set of traffic lights and then fires up again when you take your foot off the brake. It means you don’t have to waste anymore fuel than is absolutely necessary or pump out additional emissions.

There’s one other potential problem with idling your car day after day and that’s to do with your catalytic convertor which is a clever little device that sits in your car’s exhaust system and works to burn off extra hydrocarbons to reduce emissions out the tail pipe. Idling a cold car, with a cold exhaust, day in and day out can see the catalytic convertor overloaded and become blocked.

Don’t worry, that’s not going to happen if you’ve warmed-up your car a handful of times, rather you would have to warm up you car hundreds and hundreds of times for it kill the catalytic convertor. The result of that would see your car pour out more harmful emissions into the atmosphere than it has to.

My apologies to all of the old wives out there, but this old wives’ tale is now dead and buried. But there are still plenty of others to go. Stay tuned for more.

UPDATE: After posting this article to our Facebook page, a couple of comments landed talking about rotary engined cars and how it’s important for them to be warmed up before driving… I hadn’t heard that before so I looked into it. It’s true. If you own a Mazda RX-something then you need to let the car warm up for a minute or two before driving off and this is down to the different metals used in the engine. The aluminium rotor housings will heat up and expand quicker than the rest of the engine, then, once the side plates catch up they’ll end up crushing the over-expanded rotor housings. Some of the guys on the AusRotary forum suggest not warming up at idle, but revving the engine at around 1500-2000rpm.