Automotive undercoating is important to help prevent rust and corrosion, especially in colder climates. Oil-based products like Krown Rust Control, NH Oil Undercoating, and Fluid Film are three popular and effective undercoating brands. “Traditional” undercoating offered by dealerships on new cars isn’t necessarily the same thing and does not prevent rust in the long term. Undercoating should be a preventative measure applied once a year.

Does Fluid Film Work?

Fluid Film is an oil automotive undercoating. You can apply this oil-based product to the exposed metal surfaces of your car, or to the under-body of your vehicle to slow rust and corrosion. Undercoating can help prolong the life of your car, especially in colder climates. Fluid Film and it’s biggest competitors — Krown Rust Control and NH Oil Undercoating — are an effective way to prevent or delay rust and corrosion.

While dealerships will almost certainly overcharge for undercoating services, you can apply Fluid Film yourself, making it a cheap, effective way to protect your car from weather and elements. Undercoating is proven to work especially well in regions with harsh winters, where cities apply salt to the roads for safety. Salt increases the speed at which metal will rust. Additionally, as temperatures rise and fall, moisture trapped inside the vehicle freezes and thaws repeatedly, putting stress on the parts of your car.

Coating the metal surfaces of your car prevents water and salt from sticking to the metal and causing rust. After application, the oil displaces any moisture that was clinging to the car — without water, rust can’t form. The oil also creeps into all of the nooks and crannies of the vehicle, providing protection in places that can’t be seen. Some undercoating products can also be sprayed inside the doors to prevent rust and help lubricate things like the window mechanisms.

Oil coating products are different from a “traditional” undercoating offered by a dealership on new cars. Dealerships will often apply some type of paint or wax to the under-body; this type of undercoating is typically not an effective way of preventing rust in the long term. Generally, the paint will start flaking off or the wax will start to crack, allowing moisture to penetrate the metal surfaces and begin corroding them.

Of course, to get an oil-based coating to work properly, proper application and reapplication must be followed. This means that undercoating should be applied every year, typically in late summer or early fall. Applying a protective coating once, such as when you purchase a car, will only protect it for that year.

The Three Popular Undercoating Brands Compared

There are a few oil-based undercoating options available, depending on where you live and whether you want a professional to do the job or you want to do DIY. Here are three undercoating options for your vehicle:

1. Fluid Film

Note: Applying Fluid Film yourself is a pretty straightforward process. Since the product contains no solvents, it is safe for use on paint, rubber, electrical connections, and, of course, metal. It can also be sprayed over existing rust.

2. Krown Rust Control

Note: A technician will put the car on a lift and spray the underside with the oil treatment. You may also choose to have your engine bay treated as well as the inside of your door panels — both areas are exceptionally prone to rust.

  • Cost: $130 to $140 for a light duty truck, minivan, or SUV; smaller vehicles may be slightly cheaper
  • Application: Professional
  • Find a local Krown vendor

3. NH Oil Undercoating

In Summary

If you live in an area that regularly salts the roads in the winter, using some sort of rust prevention is critical to making sure your car lasts as long as possible. Whether you chose to go with a professional application or a DIY kit, it’s hard to go wrong products like Krown, NH Oil, and Fluid. The key to rust and corrosion prevention is to be as proactive as possible and apply the product every year.