As part of my dads business we had a Radiator shop. I never got involved with it, I stayed away from that whole area. But I did pay attention to some things. The paint he used back then, 50's thru the 80's was a tarish or rather oil type of paint. It was very glossy and this did dull out some after time. dried pretty fast and was very thin. It smelled almost like guys putting a new finish on a road surface. It is probably illegal in California now. I use Johnson's radiator paint I buy online. Same effect but does not smell like the old product my dad used. I asked my dad about this a few years before he died and he said it was so black it covered very fast and it was put on thin, the heat would dissipate better. primer and shooting it with a heavy paint ruins the whole purpose of the radiator. My Dad retired in the 80's from the business so he had no idea what they were using a few years ago, but he supposed that things related to it, had not changed.