How many spray cans of Fluid Film, or PB Blaster surface shield are needed?

[Jay11]

to bathe my 98 Ranger's underside-mainly just the frame? It’s a Texas truck with zero rust—basically a desert miracle—so I’m mostly doing this for the "aesthetic," but I’ll take the protection as a side dish. I like the convenience of a spray can, but I’m not loyal to above, or any brands. So what’s your favorite flavor of undercoat for a standard cab, and how many cans do I need before this truck starts looking like it belongs in a showroom instead of a sandstorm?

 

[Shran]

Surface Shield is my go to but it's basically an oily grease in aerosol form. It doesn't really "dry" per se and the first time you drive down a gravel road it'll pick up every bit of dust. It ends up looking like you have old oil leaks everywhere. That's totally fine for me. 2-3 cans of it will be more than enough to do everything. Fluid Film is a similar product IIRC, but more like a thin oil. Both products are kind of a pain to work around afterwards, if you are on a creeper and rub yourself on something you coated, you will be wearing it. It is way better than the "drain oil" method though... 25% diesel fuel/75% used engine oil sprayed on with a weed sprayer... that works very well to prevent rust but man is it messy.

Neither product will end up looking like something that belongs in a showroom. If you're going for looks AND function, spray on rubberized undercoating will be the best choice. It'll creep into tight crevices and it dries to a hard rubbery texture. Paint would be my 2nd choice.

Either way make sure you go over anywhere that has seam sealer and reapply it if it's cracked & shrunk, which it inevitably has in the heat down there, before you undercoat.

 

[Curious Hound]

to bathe my 98 Ranger's underside-mainly just the frame? It’s a Texas truck with zero rust—basically a desert miracle—so I’m mostly doing this for the "aesthetic," but I’ll take the protection as a side dish. I like the convenience of a spray can, but I’m not loyal to above, or any brands. So what’s your favorite flavor of undercoat for a standard cab, and how many cans do I need before this truck starts looking like it belongs in a showroom instead of a sandstorm?

Personally, in Texas, I wouldn't do it. If you want undercoating for that region, get one that cures to a hard surface. Fluid film remains oily/greasy. Dust is going to stick to it and look awful. The hard cured coatinhs can be washed repeatedly without removing the coating.

Those soft coatings are meant for the regions where salt and brine are used heavily on the roads. My understanding is that You apply it just before winter sets in and it protects the vehicle throughout all the yucky, wet, slushy mess of winter. By spring, especially with a couple washes, it's almost gone. Next winter, re-apply.

If you do apply something, I would strongly recommend you try to get it into voids and hollows, like inside tubular frame pieces that have access holes, not just on easy-to-reach surfaces. In between door panels is another spot to coat. Those hidden voids are where rust loves to grow unseen until it's too late. Ask Jeep owners about that.

 

[Jay11]

I was five seconds away from going "Bob Ross" on my truck’s undercarriage with enough rubberized coating to seal a submarine. I did a test patch, stepped back, and felt like a genius. It looked factory-fresh. It looked sleek. It was like Picasso's personal touch.
Then I stumbled onto FordTechMakuloco and a few other gurus online, and it turns out my "genius" plan was actually just a fancy way to gift-wrap a frame for a slow, painful death. Apparently, rubberized coating is just a waterproof sleeping bag for moisture. It traps the salt and water against the metal like a toxic relationship, and by the time you realize something is wrong, your frame has the structural integrity of a wet taco shell. Have you seen this? it's shocking.
So now, every time I go into the garage am staring at these three clearance cans from Advance Auto-looking at them like a confused cow staring at a new fence—just blinking and wondering where it all went wrong, but kinda glad I guess. Talking about paint that was actually my next bright idea, just paint the whole thing, but then the internet (bless you, Mr. G) slapped the paintbrush out of my hand and pointed me toward Fluid Film and wool wax and here we are just gobbling up this knowledge. That paint idea is still on the table though.

 

[Jazzer]

Fluid Film is sheep grease, lanolin based. It creeps into crevices. Noxudol gets good reviews.

I use five cans of Fluid Film each fall, getting the underside and inside doors and tailgate.

Rubberized coatings, as you found out, will crack and hold salt and moisture.