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Toyota 4Runner 1984-1995: How to Rust Proof Undercarriage

Rust can destroy the undercarriage of your Toyota 4Runner quicker than you think. Here are the best solutions for getting ahead of the problem.

By Charlie Gaston - January 21, 2016

This article applies to the Toyota 4Runner (1984-1995).

Just because the Toyota 4Runner is known to experience a moderate to high level of rust, particularly in areas where there is salt, an occurrence more commonly associated with locales near the ocean, doesn't mean you can't take deliberate measures to ensure the protection of your vehicle's undercarriage. Salt is also very common during winter months when it's used to de-ice roads. Let's examine all of your options in detail. You'll be able to carefully weigh the pros and cons of each and make an informed decision on which method is best for you.

Toyota 4Runner How to Rust Proof Undercarriage infographic

Materials Needed

  • Undercarriage spray cleaner
  • Water hose
  • Protective coating

Step 1 – Clean the undercarriage

Before getting started, it's highly recommended that you take a moment to clean all mud, dirt and salt from the undercarriage of your 4Runner. Undercarriage spray cleaners are widely available at a price of around $15 and are said by many Toyota owners to deliver incredible results. You may also want to use a warm power hose.

Figure 1. Use a warm power hose to loosen and remove debris.

Pro Tips

  • Jack up your truck to gain more access.
  • It's recommended that you use a shop creeper to access the various parts of your undercarriage safely and quickly.

Step 2 – Apply a protective coating

Apply a protective coating to the entire surface of the undercarriage. POR-15 Rust Preventative Coating is the go-to product for the 4Runner. This high-performance product can be applied directly to your undercarriage (even if there is rust present already). A high-performance anti-corrosive agent, POR-15, will stop future rust permanently. This product retails for around $35 online.

POR 15 anti-rust product
Figure 2. The success of this product happens in the curing process.

Pro Tips

  • Anti-corrosive products prevent rust from eating through your frame and chassis. Other brands/products include Rust-Oleum Rusty Metal Primer and 3M Rust Fighter. When applying any primer, it's recommended that you prep the metal by sanding it down. Once this is done, apply your rust converter.
  • If your undercarriage doesn't show any signs of corrosion, consider applying Rhino Lining(s). This industrial-strength coating is highly effective in protecting your undercarriage from exposure to salt and other harsh elements. You'll need to apply the product annually, as well as wash your truck regularly in the winter, but rust will not appear on your frame or chassis.
  • Fluid films are another great option. Another type of anti-corrosive, protective coating brands, such as Eureka and Amsoil, are top players in this space of the retail market.

Step 3 – Add more paint

After treating areas where there is rusted metal, you may want to consider adding another couple coats of paint. You should have already prepped and primed the metal, as well as added a rust converter. Now, finish the job with a Xylene-based paint. We recommend considering a 4Runner favorite such as Rust-Oleum Stops Rust Hammered Metal Finish paint. Apply a second coat within four hours of applying the first. Be sure to lubricate the entire undercarriage to fully protect your truck against future rust.

paint to protect from future rust
Figure 3. Apply your chosen product liberally.

Pro Tip

  • You can paint the undercarriage grey, if you prefer. Other colors are also available.

Step 4 – Check for signs of peeling

As time goes on, be sure to check for signs of peeling, and touch-up as needed. Some 4Runner owners have said they saw peeling that lead to the accumulation of rust, particularly when it came to rubber coatings. To combat this problem, carefully monitor your undercarriage regularly, particularly during winter months and after off-roading, and stick to trusted brands. As well, always follow the manufacturer's instructions to the letter when applying each application.

Look for signs of peeling
Figure 4. Look for signs of peeling.

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