Engine Idle from cold - why is it bad?

[stimshady]

Can anyone explain? (and is there proof or just 'what people think'?)

[2mad]

There's more load on the valve gear when the engines idling and it takes about 10 to 15 minutes for the engine to get to full operating temperature so its better to run the engine at low rpm but with the drive train moving.

[Munter]

Does the speed of the flame front change with temperature? Will it take longer to burn with significantly cold air and fuel...

[Daston]

Also with it sat Idle the engine oil may warm up but the Gearbox and Diff will still be cold.

[blitzracing]

A cold engine has more fuel put into it, that can lead to the oil being washed of the cylinder walls as the fuel drops out of suspension in the cold engine and this can lead to high high cylinder wall wear. On top of that you may not get enough oil splash from the big end journals at idle to lubricate the underside of the pistons and cylinder that makes matters worse. The bit about the cam load is also correct, so the best thing to do is drive the car away as soon as you can, but don't thrash it.

[stimshady]

Thanks...
i always move away quickly and keep the revs low until hot but now i know why i'm doing it!