We are frequently asked if VHT Engine Enamels can be painted over a primer or other old paint on the engine. No primer will take the high temperatures required on an engine block. Therefore, primers are not recommended. If the old paint is intact, lightly sand to a dull finish before applying VHT Engine Enamel over it. The topcoat is only as good as the base coat or condition of the metal. If the substrate gives way, the topcoat will follow.