Undercoating, Kroil, Fluid Film, Used motor oil....?

Hey all, I live in the rust belt (MA) and I want to protect the underbody of my winter beater.  I have read that Kroil or Fluid Film works really well as it soaks into the metal and that rubberized undercoat can trap moisture in.

So what say you? what do you prefer and why?

We've been using fluid film with good results.  Exepensive but mostly a one and done.  Will tell you in 5 years if it works...

In reply to 84FSP :

Do you drive down a dusty dirt road after or does it dry/cure?

I grew up it salty Quebec. People there would spray their vehicles with kerosene, even the exterior below window level. Come spring they would wash off the exterior. It seemed to work as well as any of the commercially available rust preventatives at the time.

In reply to tjbell :

I unsuccessfully tried the mineral spirits/toilet wax ring/motor oil sprayed with a garden sprayer experiment. I didn’t take my time and mix it at the right temperatures etc. but it’s worth a shot.

Also chain-saw bar oil is supposed to stick better to things if you go that route.

Put a very small hole in your rear main seal. My gmc had this special feature when I got it that would dispense two quarts of oil per tank of gas. Kept the frame and undercarriage of my 03 GMC rust free. The rockets still rusted but everything else underneath is like new just coated in oil. 

The bonus is you basically change your oil every three tanks of gas or 1000 miles. 

I am a used oil user. 300k and 15+ years of Ohio winters and we are 98% rust free. 

I've used Fluid Film, in no small part because it's convenient. It doesn't harden like a proper cavity wax, though. I've never tried it, but I recall reading about an old-time homebrew that was equal parts boiled linseed oil, paraffin, and WD-40; BLO is a hardening oil, so it should be more durable and less prone to collecting dirt.

Professor_Brap said:

I am a used oil user. 300k and 15+ years of Ohio winters and we are 98% rust free. 

May I inquire how you apply such a thing? Garden sprayer perhaps?

In reply to ebonyandivory :

I used a garden sprayer for a long time, then switched to a hammer store paint gun. 

Pro tips: 
1.  put down a tarp. (free from hammer store) 

2. put the car on jack stands and power wash it well, and get it dry. 

3. don't be afraid to spray it thick. I use used motor oil. 
 

Used motor oil thinned w/ kerosene. New oil will not stick. 

I've heated the oil/ kero mix on a stove (not direct heat, coffee can w/ mix in a pan of water) and applied w/ garden sprayer, it was kinda ok application. Pneumatic siphon spray gun is much better and gets places garden sprayer won't, no need to heat either. this one at HF. 

In reply to Professor_Brap :

Is “hammer store” the new GRM version of hardware store?

ebonyandivory said:

In reply to Professor_Brap :

Is “hammer store” the new GRM version of hardware store?

Harbor Freight. 

I read that Fluid Film, when warm, has the consistency of latex paint. So can't you apply it with one of these from the hammer store?

Just curious as I don't have an air compressor, and don't want to buy a million spray cans.

i think you could just apply the fluid film in a gallon pail with a brush if you could get under your car. 

tjbell said:

In reply to 84FSP :

Do you drive down a dusty dirt road after or does it dry/cure?

It mostly cures but not fully.  It doesn't seem to pick quite as much skuzz as oil or wet undercoating.  The sell point for me was the extra long hoses you can use to wet out frame areas and nooks.

The con is cost (buy the case on amazon) or the tank that you use an airline as propellant.  This is supposed to be a bit thicker as it isn't as thin but haven't tried it yet.

Used motor oil is a carcinogen and really shouldn't be sprayed anywhere.

It looks like a generic pneumatic sprayer but comes in a 89.95 kit with a gallon.  Or you can buy 5 gallons for ~200.

Fluid film is keeping my truck looking almost new underneath after 2+ winters.  My last one got really crappy underneath after 2 winter and no protect

Fluid Film can indeed be sprayed with a paint sprayer.

IMO an electric sprayer works better than the air-powered one that Fluid Film sells, unless you are a fan of breathing aerosolized sheep hindquarters.  (Fluid Film is mostly lanolin)  Used a Black & Decker to do a truck, worked really well.  Only "gotcha" was turning the cup/pickup tube around backwards so I could spray upwards.  Much easier than flipping the truck upside down

It's not a one-and-done though.  It does creep in to cracks and crevices but it also does get blasted away since it stays liquidish.  It does "dry" but to a consistency somewhere between Vaseline and sour cream.  (Worst Pringles flavor ever)  Need to apply it at least once a year, more if you regularly go through car washes that blast the underside.

I just had mine done with a Krown treatment.  I mostly chose Krown because they had the closest location at 8 miles away.  The other commercial brands were 100+ miles.  My 94 Fordzda Branger was (my guess) a snowbird truck.  Carfax showed always a PA title, but the sunfading on the paint, the low miles, the drooping headliner, and the ridiculous lack of rust means it likely spent its life back and forth from Tampa behind a Holiday Rambler.

The treatement took about an hour, it was $129 plus tax (around $140), and it looks fantastic.  The product must be tinted dark.  I can still see the stuff under it, but it's much darker under there.  The truck came back to me looking like a skim coat of frozen black coffee was on everything under the truck.  In the last month, it has stayed, and I believe the claims about the stuff penetrating and spreading out.  My backup lights suddenly work, my driver's side window used to chatter on its way down and now it doesn't, and a squeaky door hings is now silent.  When  I pulled the taillight housing off, I noticed that the whole length of the screw threads were stained dark with the stuff.

It's some kind of liquid paraffin I suppose.  At least that's what it smelled like for the first 20 minutes as it burned off the exhaust.  It smelled like the smoke from an extinguished candle.  They warn you to not park on a pretty driveway for a few days, and I will concur.  It drips oily stuff for a while.  Mine seemed to stop dripping after three days.  The drill holes in cavities and spray a fine mist of the stuff in the cavity, then plug the hole with a rubber grommet.  Same for the doors and rockers (if there isn't any hole already)  They focus on spraying everything that isn't the pretty outside part of the vehicle; door jambs, inside cavities, complete undercarriage, etc.  Then when they're done, the wash the vehicle to get any of the overspray off the outside.

We just got our first salt, so I'll keep tabs on it.  I found a 94 pickup that had next to zero rust and I wanted to help keep it that way.

84FSP said:

It looks like a generic pneumatic sprayer but comes in a 89.95 kit with a gallon.  Or you can buy 5 gallons for ~200.

I use Fluid Film too. I just use the spray on cans though.

It's non-creeping once it dries (so it won't self-heal), but for areas that see more direct road spray type abrasion I like CRC SP400.  It's thick and waxy once dried and pretty durable.  And you can spray on more coats to build a thicker layer.  And you can always fluid film over it to get into the crevices better.  Plus, SP400 over black paint is pretty decent looking too.  

Definitely not Kroil--Evaporates quickly and far too expensive.

Kroil is for corroded fasteners.