Painting engine?

I've read the great paint debate on which red is right, and on mine there are some parts that look red and some look more orange, and I just got wondering if exposure to forty years of oil, gas and other chemicals or that there are 3 different types of metal involved (cast iron, sheetmetal, and aluminum) could be a factor in the color difference.
Can I prime the parts? If so what kind of primer? Plan on using spray cans. If my last guess is correct than this should give an even background for the paint and result in an even color. Or either I am thinking way too much.
Thanks
Mr. Coffee