Anyone have experience doing a 4runner frame with Cosmoline RP-342? I'm mostly curious in areas where there is rust do I need to paint it with some type of rust converter after I wire brush and descale it? Or will the RP-342 work like fluidfilm in that it just stops what rust is there and prevents future rust?

I'm leaning to this stuff because it's thick, lasts, and black so it looks good. Fluidfilm in Hawaii seems like a bad idea it rains A LOT here. I also really wanted to do Eastwood Rust encapsulator plus paint but there is no way to get it here. They don't have a retailer and no one will ship. So I'm stuck finding products that I can get here.

I'd kinda prefer to do some leg work descaling and cleaning it and then painting it with a rust converter paint so if you have any suggestions there too besides Eastwood of course. I'll see what's available here but it's pretty limited! Thanks!

I live in Ewa Beach. I have a 2021 and my frame didn't rust at all in the last 2 years, but obviously yours is another 10 years older. I'd think that you could just do a rust encapsulator and maybe paint over it, depending on which one you use (if needed). I'm moving back to the east coast and fluid filmed my truck about a month ago. It seems to be holding up well even given the amount of rain we have gotten recently. I've even gone up to Peacock Flats and gotten it muddy. I don't see why fluid film wouldn't hold up to our rain. Fluid film or PB Blaster Surface Shield should be more than adequate for what we have in Hawaii. I only Fluid Filmed the underside because I plan to head up to the mountains and ski after I move.

The Toyota Tundra forum, the first gen are pretty much the "PRO"s on frame rust. This is one of the vehicles where there were frame recalls from the rust. They have tried everything, noted the results over years time.
I can tell you from experience with the Cosmoline, it looks good up front, for now, but it will rust underneath it over time. In a few years it dries out and rust starts again underneath it.
The rust converters are by far the best way to go, heavy and hard pressure washing to clean the frame and get rid of all the scale, road grime, dirt and mud and let it dry. Then use a strong degreaser/acid like Castrol Super Clean or even Wesleys Bleach White. Both of these have a acid in them that eats road grime and dirt. Put it in a pump up sprayer and spray the DRY frame down and you will see the frame start melting off brown liquid, this is road grime, and everything else. Spray it down a few times and pressure wash it again hard and heavy. This basically strips everything off the painted surface and exposes all the rusty stuff around the welds and such. Also after you expose all this, the surface rust will pop out and flash rust and look worse. Dont be scared this is good, use a rust converter and go over everything. The easiest way is to get the sprayable rust converter and put it in a small pump up sprayer like the hand held 2 quart sprayers you pump up, and spray the whole frame front to back top to bottom. By the time you get around from one side to the other, front to back, you can start over again where you started. Do this twice and you can pretty much completely eliminate any rust. The rust converters like Qurox and "chemical store" rust converter actually eats the rust, and chemically converts it into a black primer. Its pretty nifty stuff. About a week later paint the whole frame with something like Rustoleum industrial paint or Sherwin Williams industrial paint. These will create a hard eggshell to keep moisture out.

Do you have to "neutralize" these convertors before painting? I thought I read that somewhere.

In the "old days", rust "converters" were called Navel Jelly and consisted of phosphoric acid. Yes, residual phosphoric acid was washed off with water. Of course, you had to be sure the item was completely dry before you applied a primer and top coat.

I've used Navel Jelly for many projects; it really works well to eliminate any rust without touching the underlying steel. Then I apply a zinc rich primer, sometimes called cold galvanizing primer. I have never had anything rust again that I treated that way.

Not the QUROX or the Chemical Rust Converter

TheRustStore.com
GCONVERT-SPRAY - Sprayable Rust Converter Gallon

These actually turn the rust into black primer. Nothing you gotta do, let it sit a couple of days or week and everything dries and then you can paint directly over it. I did some studying into it, something something chemical reaction, refined soybean oil, coating, conversion, ect. There is a chemical reaction that turns the rust into something else, and in the drying process it coats everything with what can only be defined as a refined soybean oil. This creates an impenetrable coating to resist water getting back into the bare metal. When this happens, the coating turns a shiny pearl purple, and within a few hours its dark colored, by the following day its hardened and black. They claim it creates a black primer coating ready to paint.
I have done everything from vehicle frames, structural steel beams, old truck wheels, ect ect. This stuff is nice cause its thin and you can put it in a spray bottle, or i like to use the hand held pump up sprayer and just pull the trigger and coat everything. It works great.

I am trying Corrosion Free Rustproofing on my 2023 Tundra, and the 2024 4Runner I got last Thursday. There is an alleged lifetime warranty if you keep up with the 18 month respray. Time will tell.

Corrosion FREE | Non-Toxic And No Drip Rust Proofing

You could spray it with a good industrial coating now when its new to seal it up and likely never touch it again. Sherwin Williams makes a hard shell epoxy industrial coating, when it dries it feels like a polished egg shell. Supposedly has all sorts of ratings on chip resistance and stuff. I normally spray my frames with Rustoleum industrial black paint and go over it every few years. I dont live in the rust belt with salt on the roads all winter, so i cant say how well it would do just a regular coat of paint every few years. Most of the coatings like GM did back in the past were like thick tar, frames lasted back then.

Great info thank you! I also just realized the cosmoline is near impossible to get in Hawaii. I think I'll go the route you're suggesting. I'm just not keen on the greasy film of fluidfilm nor having to yearly reapply. I don't might spot treating and touch up paint. I also prefer it be clean and dry underneath so in the case of something leaking I can actually tell ;)

I can tell you that a lanolin product such as Fluid Film will be one of your best defenses against rust. I would rather deal with getting grease on me than dealing with stripped bolts, rusted out frame, etc...

Here in the North East, our harsh weather and salty roads in the winter will accelerate rust pretty quickly. Regular metal prepping and painting doesn't really last out this way as much as the South and West Coast.

IMO I would not use anything that creates a hard shell on your frame because eventually it will crack and moisture and dirt will get in their and start rusting it out.

If I were you at minimum just spray fluid film inside the frame, doors and rocker panels. At least that way you are pretty well protected and you won't see it anyway but it will stop the rusting from the inside out.

I was in Kauia last year and I was amazed how many old Toyotas were out there! I was so jealous too haha. It seems like the body's start to rust out before the frames from what I saw.