I don't know about using automotive primer for metal figurines, cars are made out of one sort of metal and the figurines out of something totally different.
If you live near a shop that retails supplies for the various "Games Workshop" games and the pewter figurines you can buy for them, you might want to pay them a visit. The best primer I am aware of for metal figurines is made by a company called Citadel Miniatures, Its specially formulated for use on metal figurines. It can be brushed on by hand or thinned for airbrush use. Its also available in a spray can. It goes down very nicely and doesn't obscure detail at all.
It is water based acrylic, but as with all acrylics, once its cured properly you can put any other sort of paint you want over it.
If you're in America, this stuff should be very easy to find.
Hope that helps you