I sprayed the underside of my Ford Transit with Fluid Film Black. I wanted to protect exposed metal from rust and keep the underside in good shape over years of driving. More than two years and roughly 50,000 miles later, I can still see the coating. I can also rub a spot with my finger and pick up black residue. Both things can be true.
Watch the Undercoating Job
Watch the full Fluid Film Black undercoating video
The Van Got Undercoated. So Did I.
I sprayed the underside of the van. Gravity handled the second coat.
I did this outdoors in the desert, lying on my back and spraying upward. It was one of the messiest jobs of my entire van build. The coating was thick enough to fall back in droplets, and my face happened to be directly below it. A lift would have let me stand and work from the side. On the ground, I spent the job looking straight up at what I was spraying. The photo is what I looked like afterward.
The Fluid Film Black Coating and My RAPTOR Spray Setup
I used Fluid Film Black undercoating. I poured it into an old RAPTOR bottle, screwed the bottle into my RAPTOR bedliner spray gun, and connected the gun to an air compressor. The RAPTOR bottle was the container and the RAPTOR gun was the applicator. The coating inside was Fluid Film Black.
- Coating: Fluid Film Black. My Fluid Film Black build notes
- Application setup: RAPTOR bedliner spray gun, reused RAPTOR bottle, and air compressor.
What I Sprayed Underneath the Van
I worked across the underside, focusing on exposed metal on the underbody, around the wheels and axles, and in the driveline area. I left the exhaust, other hot parts, electrical components, and plastic fuel tank alone.
| What I called it | What to look for underneath a Transit |
|---|---|
| The metal undercarriage | Underbody floor pan, longitudinal side members or rails, crossmembers, and mounting brackets |
| The axle area | Rear axle housing and the differential housing in the center of the axle assembly |
| The inner wheel area | Inner wheelhouses and nearby suspension parts, such as front lower control arms and rear leaf-spring brackets |
| The drivetrain underneath | The driveline is the more specific term here. The driveshaft, also called the propeller shaft, carries power toward the rear axle and differential. |
That’s a guide to the names of the areas I’m describing. The wheelhouse is the body structure around the tire. The control arm and spring brackets belong to the suspension, and the brakes and wheel-mounting surfaces are separate assemblies. Ford’s upfitter manual calls for keeping coating off brake components and the exhaust, and for keeping paint off wheel-clamping contact surfaces. Ford Transit corrosion-prevention guidance, section 5.13 · Ford Transit chassis parts
Why Coat the Underside of a Van?
An intact coating acts as a barrier between metal and what the road throws at it. Water and road salt can reach exposed steel, while grit and debris can wear through a finish. A suitable coating helps keep those contaminants away from the surface. I did the job to reduce the chance of rust and preserve the metal underneath my van over the long haul.
Fluid Film describes Black as a non-drying, lanolin-based corrosion protectant. The wet film can move into seams and helps shield the metal from moisture and road salt. That soft finish is consistent with the black residue I picked up when I rubbed a coated spot. Fluid Film Black technical data
What I Found After Two Years and 50,000 Miles
The black layer was still visible on the metal where I checked. Road dirt and grime had stuck to it. When I rubbed a coated spot with my finger, some black material transferred. Driving hadn’t visibly stripped the coating from the areas I checked, but deliberate rubbing or wiping could lift material.
If I did this job again, the first thing I’d change is how I reach the underside. Being able to stand and get out from directly below the spray would make a bigger difference to the experience than anything I remember about the gun.