Warming up your car in the morning: Why this habit can damage your engine (and earn you a fine)

© Rostislav_Sedlacek/Shuttestock

On mornings when the winter cold makes us regret getting out of bed, it is common to see some motorists starting their car while it is defrosting of their windows, so that the mechanics warm up. This tradition, passed down from generation to generation and often recommended by old mechanics, has its roots in a time when automotive technology was very different. But times have changed, and this habit could now play tricks on you.

An outdated practice that threatens your engine

Modern engines are nothing like those of thirty years ago. Equipped with sophisticated electronic injection and multiple sensors, they adjust the air-fuel mixture in real time according to the temperature. Today's oils, which are much more efficient, provide almost instantaneous lubrication of mechanical parts. ” Warm up ” its engine when stopped becomes not only superfluous, but potentially harmful.

The real danger lies in the accumulation of unburned fuel. When the engine is idling cold, combustion is imperfect. Fuel residue mixes with the engine oil, gradually reducing its lubricating properties. This premature degradation of the oil can lead to accelerated wear of mechanical components, particularly piston rings and cylinder walls.

The hidden cost of a false good idea

Beyond the potential mechanical damage, this habit directly impacts your wallet. An engine that idles for 10 minutes every morning unnecessarily consumes nearly half a liter of fuel. Over three winter months, that’s more than 45 litres of wasted fuel, or the equivalent of €80 literally going up in smoke when you could have used it to get around.

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But the bill can be even steeper. Few drivers know this, but leaving your engine running when stationary is illegal in France. Article R318-1 of the Highway Code states that it is forbidden to leave your engine running when parked. Most experts recommend that you do not leave your engine running while you’re stopped for more than 20 seconds. The offence is punishable by a fine of €135. This measure, initially designed to combat urban pollution, applies both in cities and rural areas.

The right method to preserve your engine

The solution ? Start and drive immediately, but gently. The first few kilometres should be done at moderate speed, without rushing the engine. This is the best way to allow all engine parts to gradually reach their optimum operating temperature.

In very cold weather only, a short warm-up time of one to two minutes may be justified, particularly for diesel engines. But beyond that, you risk damaging your vehicle more than preserving it. Manufacturers themselves confirm this: modern cars are designed to start and run immediately, even in cold weather.

The only exception is older vehicles, particularly those from before 1990. Their less sophisticated design may require a longer warm-up time. But for the vast majority of today's vehicle fleet, this practice is definitely a thing of the past.

• Warming up your modern engine while stationary degrades the oil and accelerates mechanical wear
• This habit wastes fuel and can cost you a fine of 135 euros
• The best method: start and drive immediately gently for a few minutes

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