Do I need to wire brush surface rust before applying Fluid Film?
You do not need to meticulously scrape or remove all surface rust before applying a lanolin-based coating like Fluid Film, as long as loose scale is brushed off. Lanolin-based sprays work by penetrating existing rust and cutting off oxygen to halt further corrosion, making extensive manual removal unnecessary unless preferred.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Spraying the undercarriage directly without overthinking it.Did this help you?
- 2Using a wire brush, hammer, or screwdriver to knock off loose rust scale before spraying.Did this help you?
- 3Leaving the rust aloneDid this help you?
- 4Spraying the metal with lanolin aerosol cans or cosmoline blackDid this help you?
- 5Scraping the rust off using a wire wheel and a drillDid this help you?
- 6Getting the truck undercoatedDid this help you?
- 7Using liquid films like Fluid Film or Wool Wax despite slippage concernsDid this help you?
- 8Testing the rusted metal with a screwdriver before lifting to ensure integrityDid this help you?
- 9Leaving minor surface rust untreated because the car will die firstDid this help you?
- 10Washing underneath the car regularly during winter to keep salt offDid this help you?
- 11Using wire brushes or sandpaper to remove surface rustDid this help you?
- 12Applying rust converter spray and protective coatings like Cosmoline BlackDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I noticed some rusting in the undercarriage. Is is something that I should be concerned about and what are some preventative measures to take so it doesn’t get worse”source ↗
“I (New England area) have a 2019 used Mazda with existing rust. At this point, is it still worth treating the rust, or just leave it be?”source ↗
“Is this rust anything to worry about and is there anything I can do myself to prevent it from getting worse?”source ↗
“I’ve seen rust converter spray but does that actually work? Seems too good to be true. If it does work do I have to paint afterwards too?”source ↗
“I don’t have the tools or anything to start taking wheels and parts off of the car.”source ↗
“I was planning on getting fluid film applied to the underside of my car this weekend, but wanted to know if I should take a wire brush to the underside of my car first and get the surface rust the best that I can?”source ↗
“I don't have a lift or anything, so I'd have to figure my best way underneath.”source ↗
“The engine cradle on my 94 park ave is starting to get some nasty surface rust, and It's the FSM jack point for the front of the car.”source ↗
“Obviously I'm worried about jack slippage with any kind of liquid film and I hear rubberized ones can make the rust worse if it isn't fully cleaned or water finds a way in.”source ↗
“I'm just not sure how fast/far the rust will spread. How long does it typically take surface rust to start impacting structural integrity?”source ↗
“Could that cause any issues with the jack possibly slipping? I was leaning towards this or wool wax, but I'm concerned about the lubricating factor.”source ↗
Where this came up
People with this problem also raised
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- 5Mechanic refused to fix rusted control arm and subframe
- 6How to fix a loose or hanging car splash guard
- 3Is severe brake rotor and caliper rust safe to drive on?