Was chatting to a mate who says that it is much better to use distilled water in a car's cooling system instead of ordinaly tap water, however he had no actual facts to back this up.

Is it true or not? The only real benefit I can see is less scale build up and will probably keep the header tank etc cleaner. I've got a good supply of it from work, so if it is better for the car, I will use it.

Cheers

Rich