Etching Primer??

Etching primer is made to be used on bare clean metal.  It is very thin when cured and you then would normally apply a regular primer and paint over that.  It will not bond to old paint, but if it's clean bare metal it will form about as good a base as possible for the other layers to bond to.  It's a combination of an etching acid (usually phosphoric acid) and zinc which form this base coat.  It is often almost transparent with a slight tint to it.

I have no idea if they make a high temperature version or if heat would be a problem.  Also the general consensus is the stuff in the rattle can is inferior to bulk can from a body shop.  Something to do with the way the zinc & phosphorus atomize (or don't atomize) in the rattle can.  But they sell a lot of it in rattle cans (Rust-o-leum, DupliColor, etc...).