Automotive undercoating is important to help prevent rust and corrosion, especially in colder climates. Oil-based undercoatings like those offered by Krown Rust Control, NH Oil Undercoating, and Fluid Film are popular and effective. 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. We have the details of how undercoating works and which brands are best below, including a comparison of Fluid Film, Krown Rust Control, and NH Oil Undercoating.
What Is Undercoating?
Undercoating is applied to the metal surfaces of your car (primarily the underbody) to prevent water and salt from sticking to the metal and causing rust. After application, oil-based undercoatings displace any moisture that was clinging to the car — and without water, rust can’t form. The oil spreads into all of the nooks and crannies of the vehicle, protecting places that can’t be seen. Some undercoating products can also be sprayed inside the doors to prevent rust and 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 paint or wax to the underbody; this type of undercoating is typically not an effective way of preventing rust in the long-term. Over time, the paint may start flaking off, or the wax may start to crack, allowing moisture to penetrate the metal surfaces and begin corroding them.
Oil-based 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. Of course, for an oil-based coating to work, proper application and reapplication practices must be followed. The 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.
Does Fluid Film Work?
Fluid Film is an oil-based automotive undercoating. The product is non-toxic — its base ingredient is lanolin, and it contains no heavy metals, phenols, arsenic, or other harmful ingredients. Available in spray cans or larger-quantity undercoating kits, you can apply Fluid Film to the exposed metal surfaces or underbody of your vehicle yourself.
Fluid Film is an effective undercoating, mechanics and customers have reported. As noted by users of the brand and Fluid Film’s FAQ, it will not remove rust, but it does stop rust from spreading and prevent future corrosion if you keep up with the yearly applications. The aerosol spray option also makes touch-ups quicker and easier to apply than some other do-it-yourself undercoating products. Occasional touch-ups throughout the year are recommended, particularly on areas that are are not protected from “road spray” (debris kicked up by the vehicle’s tires).
While dealerships and service centers may charge high prices for undercoating services, you can apply Fluid Film yourself, making it a cheaper, effective way to protect your car from weather and elements. Fluid Film is widely available at auto parts stores and other retailers, including websites like Amazon and farm equipment retailers like John Deere. Do-it-yourself undercoating can be messy and requires some preparation, such as sanding existing rust and washing the vehicle’s underbody, but may be worth the effort if there isn’t a professional undercoating service near you, or if the professional services near you are costly.
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. Each of these companies offers different options for application, warranty coverage, and price points; we have the details in the next section, to help you find the product that best fits your needs.
The Three Popular Undercoating Brands Compared: NH Oil Undercoating vs Fluid Film vs Krown
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 DIY. Here are three undercoating options for your vehicle:
- Application: DIY. Applying Fluid Film yourself is a pretty straightforward process. (See the video tutorial below.) Since the product contains no solvents, it is safe for use on most paint, rubber, electrical connections, and, of course, metal.
- Available products: Fluid Film is available in aerosol cans, gallons, and pails. It can be purchased by itself or in a kit, which includes a spray gun and other accessories for DIY application.
- Cost: About $10 for a single spray can; $30 to $60 for a pack of three to six cans; $50 for one gallon; or $200 for a five-gallon pail. Fluid Film undercoating kits are available on Amazon for around $150.
- Warranty: No warranty is offered for your vehicle, but there is a one-year shelf life guarantee on aerosol Fluid Film products.
- Buy Fluid Film on Amazon or find another Fluid Film dealer near you.
Krown Rust Control
- Application: Professional. 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.
- Available products: Krown’s undercoating is applied professionally, but the company does sell aerosol cans of its Rust Protection & Lubricant.
- Cost: Professional application by Krown costs anywhere from about $130 for two- and four-door cars up to $150 for larger vehicles like crew cab pickup trucks. Rust Protection & Lubricant aerosol cans (for touch-ups or a wide range of other home and automotive uses) are around $10 each.
- Warranty: Krown offers warranties for new and used vehicles. Both warranties require that you apply Krown annually and keep a record of the yearly applications. The warranties include body panel rust protection, with damage repaired or replaced at no charge up to the current Red Book value of the vehicle. New vehicles must have been purchased less than six months before applying Krown to qualify for the warranty, while the used vehicle warranty is good for a maximum of 60 months (with unlimited mileage).
- Find a local Krown dealer.
NH Oil Undercoating
- Application: DIY or professional
- Available products: One-gallon and five-gallon containers of undercoating are available in black or clear-coat colors. The undercoating kit includes the amount of undercoating you choose, plus a spray gun and wand.
- Cost: Buying directly from NH Oil, a DIY undercoating kit costs between about $135 and $300. Touch-up cans sell for about $30. You can also contact a local NH Oil vendor for professional pricing.
- Warranty: Participating dealers offer a nationwide, transferable guarantee for the life of the vehicle, as long as NHOU is applied annually.
- Find a local NHOU dealer.
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If you live in an area that regularly salts the roads in the winter, using some sort of rust prevention can help your vehicle last longer and avoid salt damage. Whether you chose to go with a professional application or a DIY kit, products like Krown, NH Oil, and Fluid Film can help protect your car from the harmful effects of road salt. The key to rust and corrosion prevention is to be as proactive as possible and apply the product every year.