POR15 is great at night only. It breaks down in daylight/ultraviolet .
Phosphoric acid turns iron oxide(rust) into iron phosphate/creates an iron phosphate coating on ferrous surfaces (steel) that primers love to stick to. One such product is OSPHO. I now use it inside rusty motorcycle gas tanks after I rattle nuts/washers/steel BB’s inside to remove the loose rust. Then I fill up the tank with 100% ospho. I just leave it for a couple of days and drain it out. Do a flush with some of this new terrible ethanol fuel or alcohol from rite aid.
Put a cap full of marble mystery oil each tankful. Works great. No more messing with any two part interior fuel tank coatings .
For exterior steel surfaces_I use Rust Destroyer red oxide primer over the iron phospate coating . It’s the one-two killer way to control rusting steel.
There is a similar product to ospho for aluminum alloys but, I can’t remember what it is.
Coca Cola is ok but I like it mixed with a good Jamacian Man rum like Mount Gay mmmm.