Having spent years as a furniture refinisher, I’ve had plenty of opportunities to spray-paint metal objects, such as ...

If you are painting a radiator that still works and is used to heat the home, the primer and paint should be rust resistant and able to withstand the high temperatures that radiators generate.

The only problem that we come in contact with is our alkaline paint stripper actually eats soft metals. So if there's aluminum, magnesium, or a pot metal on the car, it'll react and it'll dissolve it.