What undercoating do you think works best there?

Best undercoating based on preference?

  • Krown

    Votes: 1 7.7%
  • Corrosion Free

    Votes: 0 0.0%
  • Fluid Film

    Votes: 7 53.8%
  • Rust Check

    Votes: 1 7.7%
  • Engine Oil

    Votes: 3 23.1%
  • Frame Rails? What the **** are those?

    Votes: 1 7.7%

  • Total voters
    13

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,006
113
Galaxy far far away
Its important to not get Fluid Film type undercoating on your frame if it still has the original GM hard wax coating. Seen reports of Chevy truck guys complaining that after applying Fluid Film, the frame wax coating turned soft and falls off exposing bare metal to rust. To repair the frame coating GM says to use Nox-Rust 121b coating.
 
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motorheadmike

Geezer
Nov 18, 2009
8,604
113
Saskatchewan, Truckistan
I am a Krown guy.

It deep creeps with capillary action. And in my experience it only "washes away" in heavy use areas. After a season of grime gets on top of it, it holds very well.

Finding a good tech who isn't frugal with the product makes a difference in how long it lasts. Touch-up with a can of it if needed.
 
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Nov 4, 2012
5,285
113
Its important to not get Fluid Film type undercoating on your frame if it still has the original GM hard wax coating. Seen reports of Chevy truck guys complaining that after applying Fluid Film, the frame wax coating turned soft and falls off exposing bare metal to rust. To repair the frame coating GM says to use Nox-Rust 121b coating.

That's probably true, but which is worse- Fluid Film softening the wax so much it wipes off easily, or the wax drying out and crumbling off on it's own after a few years? Neither option is good and I don't know that either one is better than the other, I guess it's personal preference.

Or just drive a Ford and don't worry about wax because the frame is e-coated.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,006
113
Galaxy far far away
The wax on my frame has fallen off yet, through it has rubbed off where I had placed jack stands. Lets just say that GM's unusually frame rustproofing makes applying fluid film type coatings on the underbody a tough call. Not sure if the sub frames on GM unibody cars like 3rd gen F bodies are also wax dipped or painted? I suppose you could mask the frame and just do the wheel wells and floor pans.
 
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Nov 4, 2012
5,285
113
The wax on my frame has fallen off yet, through it has rubbed off where I had placed jack stands. Lets just say that GM's unusually frame rustproofing makes applying fluid film type coatings on the underbody a tough call. Not sure if the sub frames on GM unibody cars like 3rd gen F bodies are also wax dipped or painted? I suppose you could mask the frame and just do the wheel wells and floor pans.

It would be great if they e-coated then wax dipped. Now that everything has hydroformed boxed frames, the metal is thinner and because it is boxed, it traps all that salt and dirt making it harder to wash out. I think Ford was the first or one of the first to box their frames and now all of those 2004-2008 F150s have rotted frames on the bottom 1" of the rail.

Fortunately I know Ford sells their frames in sections and they are designed to be repaired, they are typically for collision but can be used for rust repair as well. I don't know about GM or Dodge but I imagine they do they same.

Sorry for my tangent... lol.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,006
113
Galaxy far far away
My Crown Vic has plastic plugs in the frame to help keep gunk out. Plus part of the frame is solid cast aluminum, a sub frame on the main frame.

Looking around online I found that Fluid Film themselves warn that their product is not compatible with some GM coatings.
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
3,953
113
Western MN
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I'm on the 'reactive' side of things
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g0thiac

G-Body Guru
Thread starter
Sep 6, 2020
659
63

SupremeSpeed

G-Body Guru
Sep 29, 2016
585
93
GA
As the title asks. Not including rubberized undercoating, because that stuff is useless. If you haven't watched Eric's video on YT, heres the link.

Great info glad you shared this. I will be doing an undercoating restoration soon.
 
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abbey castro

G-Body Guru
Oct 31, 2015
533
93
Harker Hts TX
My take: My 87 was the family daily driver for 15yrs in Southern Michigan. I washed it every week both outside and undercarriage all the time. The dealer had sprayed on a tar like substance that really did a good job for so many years. After I took it all off via blasting there was no rust on the body and only surface on the frame. I've sprayed every crevice on all body joints as well inside the frame rails (hundreds of holes) with CorrossionX (a Mil Spec) spray. Although I live in Central TX and haven't driven the car in the rain since the off frame, this stuff flowed well into the crevices and leaked all over the floor from the heavy spray applied. Don't know if it is good or not. For the rust belt guys: Wash, wash, wash underneath is the best you can do. Stay out of puddles (salt baths) Pic your favorite brand and apply liberally!
 

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