Eastwood's radiator black is not extraordinary, iIt's just aerosol enamel. They word their descriptions cleverly for marketing purposes, and the price reflects it. Their company may provide convenience to the less infomed hobbiest, but they offer nothing that can't be purchased at a jobber, or sometimes a hardware store. I've been painting radiators for years with enamel or urethane which have hardeners. One coat shot over a light coat of epoxy. SEM has aerosol gloss black too, it's a professional product, covers well and dries quickly. SEM is a major supplier to the autobody industry. I don't use aerosols much but if people have success with Rustoleum that is another option. Low quality aerosols offer poor coverage. Aerosols are high in solvent content, and in general don't cover well. Cheap ones cover even worse.
