Not only but also, wherever there is scale. Here it is widely used as a cleaner, I buy mine in the supermarket in the household cleaning section in 5 or 10 litre 'bidons' at either 12 or 14 percent, its called 'ménager' to distinguish it from the cooking version. If you want to be posh there are even versions with a perfume additive
I think, but not sure, some owners of classics flush the car rad out with it - must check up on that as I will be cleaning out and replacing the coolant in my 13/60 this year.