Warming a car’s engine by idling for extended periods in cold weather can actually do more harm than good. A trusted automotive expert explains why this practice is problematic and what drivers should do instead.
Winter brings its own battery challenges. A healthy battery may turn the engine over, but it does not reliably recharge until the engine is running and the alternator is putting out charge. At temperatures as low as -30 °C, a cold battery accepts very little current, which means it can struggle to start the car even if it has some energy left. This is why relying on idle time to keep the battery charged is a poor plan during a deep freeze.
Moreover, repeatedly starting the engine and letting it idle for long stretches does not protect the engine from wear. When the oil is cold, its lubricating properties are reduced, and frequent startups can accelerate wear. If the engine and its oil are already somewhat worn, deposits may form more quickly, further degrading performance. A practical approach some drivers use is to drive on highways for a short while, allowing the engine to reach operating temperature and burn off carbon deposits by briefly running at higher revs.
Another consideration is how a car sits during the winter. If the vehicle is left idle for long periods, the battery can discharge despite occasional startups, especially when modern cars have systems that draw power even when the engine is off. If staying unused for the season is inevitable, it is sometimes recommended to start the engine a few times during thaw periods and run it for a longer stretch, at least thirty minutes, to help the system recover. Yet this is not a foolproof method for preserving a weak battery or preventing energy drain, particularly if the battery is old or if there are devices that steadily drain power when the engine is not running.
In summary, extended idling to warm up a car in cold conditions is not a reliable or safe way to protect the engine, battery, or oil. The best practice is to drive gently after a cold start, allow the engine to reach its proper temperature, and avoid prolonged idling. Modern vehicles benefit from being exercised on the road, which helps the battery, fuel system, and oil reach optimal temperatures faster and more efficiently.