Best Car Undercoating? Let's find out! Is Flex Seal the Best Rust & Salt Protection?

Jan 2020/15 min/6 products tested

The verdict

1
CRC HD Corrosion Inhibitor
avg finish 1st place (dirt/water, stationary, and pressure-washer tests)
“I'm really impressed with CRC. It definitely did the best coming in first place.”
Buy on Amazon ↗
2
Flex Seal
avg finish 2nd place
“Flex Seal actually did very well. It survived the pressure washer and there is a little bit of rust that's formed where the rock chips occurred. However, it definitely beat out most of the competition. In my opinion, a second place finish.”
Buy on Amazon ↗
3
WD40 Specialist Long Term Corrosion Inhibitor
avg finish 3rd place
“it did really seem to cause a lot of issues for WD-40 Specialist which finished third, Fluid Film and Corrosion X fourth.”
Buy on Amazon ↗

Also noted
Fluid Film
“it did really seem to cause a lot of issues for WD-40 Specialist which finished third, Fluid Film and Corrosion X fourth.”
Buy ↗
Also noted
Corrosion X
“it did really seem to cause a lot of issues for WD-40 Specialist which finished third, Fluid Film and Corrosion X fourth.”
Buy ↗
Budget pick
Fluid Film
“Fluid Film is the most affordable product we'll be testing. It costs right at 85 cents per ounce.”
Buy ↗
Avoid
Corrosion Block
“While Corrosion Block definitely beat used motor oil as well as the control, it definitely is not as good as most of the other products.”
Buy ↗
Also noted
Flex Seal
“my fear with any sort of rubberized coating is the long-term effect of using it. If you've ever worked on a car that's had a rubberized undercoating, it can cause a lot of problems in frame rot over time.”
Buy ↗

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