Say I've got a bit of surface rust on my frame. Say I want to wirewheel it off and go over the whole thing (hell, maybe the axle too) with some shiney black paint. Is tremclad going to prevent rust as well as POR-15 or is it a waste of time?

I figure any paint will work as long as it keeps moisture from the metal. POR-15 will work better if there's rust on the metal but presumably the wirewheeling will take care of that.

Any thoughts?

 

Tremclad is sold as a rust paint so..

I did my frame rails with it but I just sprayed them off with water

 

Don't waste your time with paint just yet. How much surface rust do you have? If it's a lot - perhaps painting it might be worth it, but I would seriously get it up on a lift and have your undercarriage pressure washed so it's as clean as possible then buy about 6 cans of Fluid Film from Canadian tire and just coat the entire undercarriage (after it's dry of course) - frame, sheet metal, suspension components, axle, etc. . This stuff should last you through the winter and protect your undercarriage as well as it will work on and slowly remove the oxidation from the surface rust. It's remarkable stuff. I'll be doing this very thing in less than a month. If Spring rolls around and you're not happy then consider painting it.

 

I've used fluid film for all kinds of stuff. It's good, but I really think sealing all that rust in with oil is a bad idea (my undercarriage is rusty as hell). The rust needs to be removed and then the metal sealed or it'll just keep rusting, as far as I know.

If I undercoat or fluid film on a dry day will the rust continue under the undercoating or will it stop?

 

Fluid film advertises, and I've seen it with my own eyes as there are still wet spots under my truck with fluid film that I put on it last year, that it protects, and as it protects with it's oily sort of waxy consistency, it also works on removing oxidation at the same time.