Minor Engine Bay Rust Treatment -Prepaint

I have had good luck with POR15, but I don't think that is what you want to use for mild surface rust. There are several brands of Rust Converter out there. The one I use is from TP Tools. You can get it from pretty much any car parts place and specially a car paint place. A lot of them contain Phosphoric Acid, so be careful. Anyway, the rust converter actually converts the chemical makeup of the rust and it turns black. It is no longer rust, it's chemical composition has changed. Any time I am dealing with minor surface rust like this, I always strip the panel to bare metal, and then treat the entire panel with the converter. That way, every little spot of rust gets treated. However, you said you did not want to strip the area to bare metal, so here is what I would do. Wire brush to get of as much loose rust as possible. Then sand the area with 220 and then 320 grit dry paper. Clean area thoroughly with some type of pre-paint solvent. NOT WITH WATER!. Then treat the entire area with the rust converter. Follow the directions for the brand you bought. When the appropriate time has elapsed, re-sand with 320 grit dry sandpaper, clean area thoroughly again with pre-paint solvent and apply a few coats of decent primer. You will have a lot of pock marks and scratches to fill in. Do that now with an easy to sand filler (a good spot filler would be best). Then final prime and paint. I know this sounds like a lot, but trust me when I say that there is no short cut to a nice looking repair that will include paint. Feel free to contact me via PM if you have any more questions.