Assuming the radiator is clean, dry, sound and prepared as detailed in the technical data sheet you could consider Rust-Oleum CombiColor Original.

It is heat resistant up to 90°C (dry heat), so as long as the surfaces being painted didn't exceed this temperature it should be OK.

But it will have an solvent smell during use and drying.

Rust-Oleum CombiColor is however an industrial product designed for exterior use or interior use in industrial environments so it is not specifically intended for internal home use.