How do you protect your underside?

So I'm wondering in advance of my purchase just what everyone does to prevent rust on their underbellies? We have calcium chloride sprayed on our roads and is turning my 03' F350 into a rust bucket. Undercoating, Fluid Film, Playdough? What says the Illuminati?

And so it begins...

Fluid film. If its good enough for the Navy to use on their aircraft its good enough for me.

I don't think that rubberized stuff is good for used trucks, it essentially seals in everything. Unless you have a perfect frame with zero oxidation or corrosion and the coating is literally perfect then it will accelerate the process.

badm0t0rfinger said:

Fluid film. If its good enough for the Navy to use on their aircraft its good enough for me.

I don't think that rubberized stuff is good for used trucks, it essentially seals in everything. Unless you have a perfect frame with zero oxidation or corrosion and the coating is literally perfect then it will accelerate the process.

Click to expand...

Thanks for the info. Probably a good move.

badm0t0rfinger said:

Fluid film. If its good enough for the Navy to use on their aircraft its good enough for me.

I don't think that rubberized stuff is good for used trucks, it essentially seals in everything. Unless you have a perfect frame with zero oxidation or corrosion and the coating is literally perfect then it will accelerate the process.

Click to expand...

This makes me want to cry. I know it’s a Chevy and all, but still .

Any videos like this of Fluid Film or AMSOIL HDMP? Haven’t pulled the trigger yet on my used 2014 thankfully as this is the shit I was worried about.

I’m in IL and roads are salted. I also have some light rust on the undercarriage generally. Frame and rockers are good, but I want his lady to last! Don’t want to slather it in some goop that will eat away from the inside.

MFNG said:

This makes me want to cry. I know it’s a Chevy and all, but still .

Any videos like this of Fluid Film or AMSOIL HDMP? Haven’t pulled the trigger yet on my used 2014 thankfully as this is the shit I was worried about.

I’m in IL and roads are salted. I also have some light rust on the undercarriage generally. Frame and rockers are good, but I want his lady to last! Don’t want to slather it in some goop that will eat away from the inside.

Click to expand...

Yeah, seeing a truck like that no matter what brand, is tough.

One of my favorite Channels has a few videos about fluid film and other rust preventatives.


I like fluid film because its what I'm familiar with, I'm sure there are other alternatives that are just as good if not better. I've heard great things about anything AMSOIL makes.

Here is from the same channel I already posted about applying it.

Glad I gave up on undercoating after first year. Did not hold up at all. I've used fluid film for seams never thought of using for undercarriage. I'll be blasting my rocker panel seam.

I use a jockstrap... not comfortable, but when things get rough...

Personally, I think FF smells horrible and after using it on my former rust bucket, there is a zero percent chance I'm going to slather any other vehicles I own in that stuff. It works great, but the smell is kind of nauseating to me. Some people like it though- smells are such a weird thing. It's also nasty to work around and attracts dust.

Maybe if it was parked outside all winter and I could easily put it on a lift and pressure wash it all off in the spring, then I would consider giving the underside a FF bath. It doesn't smell as much when it's cold, although a fresh coating under the whole underside of the truck is going to reek bad for a long time, cold or not.



I have been, and plan to continue spraying any visible surface rust with a rust converter, then top coating it with a good quality spray paint.

I use this for the rust converter.
https://smile.amazon.com/gp/product/B0009LPJ0Q/

I use Rustoleum Professional flat black and buy the big cans by the 6 pk.
https://smile.amazon.com/gp/product/B01MZFKX8B/

For the rockers, door, and tailgate bottoms/pinch seams I'm planning to use something purpose made for it.
Something like this: https://smile.amazon.com/gp/product/B00TVH7R5O/
or this: https://www.amazon.com/dp/B0741FHDPF/?tag=fordraptorforum-20

Great post, lots of information. Spring time I will look in to this and try to do it myself