We have a joke here at my work -

How do you turn a radiator into a sprinkler?

Fill it with DI water...



Stay with distilled. DI will pull ions from the metal. Since a radiator core tubi stypically something like 0.010 - 0.013" thick it doesn't take long for it to break through. Use distilled. DW is ionically balanced (with some ions removed) while DI is completely deionized.