5 minutes is sometimes necessary in very cold conditions to prevent things re-freezing as you move off.
Again, if you're going to drive 20 or more miles and damp acids will evaporate anyway. Switching off soon after startup has a very detrimental effect.
I'm told that the issue is less a problem with diesel engines as the fuel itself has lubricating properties.
More important is letting it idle for 2-3 minutes after quick driving if your car is turbocharged. Switching off an engine with a turbo at 600 degrees is bad news.
Turbochargers create LOTS OF HEAT. |