In winter, many motorists idle their engines for several minutes to warm them up before they hit the road. But do we really need to wait that long? The quick answer: no. According to Transport Canada, "most cars take only about 30 seconds to warm up the engine to the temperature needed to drive, even in extremely cold weather. It is therefore good to keep it running for a while, but it is not necessary to wait five or even ten minutes before taking the road. In fact, in the long term, it can even become harmful. According to the trade magazine Road & Track, a vehicle that idles for too long promotes the dilution of motor oil. The best way to warm up your vehicle is to drive it very calmly until the temperature rises and allows normal use.

An old belief

This false belief that a cold car takes several minutes to operate properly goes back to a time when vehicles were equipped with engines equipped with carburettors. However, carburettors have been abandoned for more than 30 years and just about every car on our roads today is equipped with an injection system. In short, unless you drive an old carburettor car, you gain absolutely nothing by keeping your engine running for several minutes. On the Internet, everything and its opposite is said about a possible preheating of the engine on a cold morning. We asked the professionals. More reliable, today's engines have a reputation for being able to start with a quarter turn in all weathers. Reading the comments on some forums, letting your engine warm up on a cool morning has become useless, the most common argument being that idling helps clog diesel engines. Yet for years we let our cars warm up in the morning.

What do the instructions say?

When reading the operating instructions for my Audi A3 Sport back 2.0 TDi, it is clearly stated on page 121: "Do not warm up the engine while it is stationary. Start immediately. This will prevent the unnecessary release of pollutants. Diesel engines have a preheating system whose duration is determined by the coolant temperature and the outside temperature. Its symbol is a kind of double loop that goes out after a few seconds. It is also specified the risk of poisoning if you run the engine in a closed room. It is still recommended to wait for an optimal engine temperature before getting into the revolutions.

What do garage owners say?

I called several garages (Peugeot, Citroen, Fiat and Toyota). They all have the same speech. Parked in the street and even in the cool of the air, you can start as soon as the preheating signal is switched off, provided you drive quietly, even if you are quickly getting on the highway. This also applies to petrol vehicles, the recurring idea is not to drive full throttle right away.

Can the fuel freeze?

During the last wave of extreme cold in France, it was in 2012, a lot of breakdowns concerned diesel vehicles whose fuel was starting to freeze, unlike gasoline whose melting temperature is about -60°. Indeed, from -15°, a thin layer of paraffin can form in the tank. And even from 0° if the vehicle contains "summer" diesel sold until 31 October. A plug then forms at the filter, the engine is no longer powered, failure. And if we are not yet there, know that there is in the most exposed regions (eastern half of the country) very cold diesel fuel with a temperature of -20°.