Is there a good primer (spray can) to stop cast iron engine parts from rusting?

Is there a good primer (spray can) to stop cast iron engine parts from rusting? I'm using Mopar engine paint on the cast iron & steel engine parts, and need to find a primer that will take the heat and not allow rust to come thru from underneath. The paint is sticking, not peeling, but parts seem to get rusty looking after a while. And I know someone will say that Mopar paint is no good, but this bleed-thru happens with VHT engine paint too.