Ultimate Underbody Rust Prevention and Chassis Protection Guide

Begin by thoroughly washing the undercarriage. Use a pressure washer with a salt-neutralising solution. Focus on the 'mud traps'—the tops of fuel tanks, inside chassis rails, and behind wheel arch liners. If you have been off-road, ensure every gram of red dust is removed, as it will prevent the protective coating from bonding to the metal. Allow the vehicle to dry for at least 24 hours in the sun, or use compressed air to blow out trapped water from boxed sections.

Inspect the chassis for existing rust. Use a wire brush or a needle scaler to remove any loose 'flakey' rust. You do not need to get back to shiny metal when using lanolin, but you must remove anything that is delaminating. Lanolin will penetrate firm surface rust and stop further oxidation, but it cannot stick to loose debris. Wipe down the cleaned areas with a wax and grease remover.

Mask off components that should not be coated. This includes brake rotors, brake drums, the exhaust system (especially the catalytic converter and DPF which reach extreme temperatures), and any rubber serpentine belts. Use heavy-duty aluminium foil to wrap exhaust components; it stays in place better than tape in the tight confines of a vehicle underbody.

Raise the vehicle using a hoist or heavy-duty jack stands on a level concrete surface. Ensure the vehicle is stable by 'shaking' it before crawling underneath. Never rely on a hydraulic jack alone. If working on a driveway, consider the environmental impact; place a large heavy-duty drop cloth or recycled cardboard under the vehicle to catch any overspray or drips from the lanolin application.

Start with the internal boxed sections. Insert the 600mm 360-degree extension wand into existing drain holes in the chassis, sills, and pillars. Depress the trigger and slowly withdraw the wand at a rate of approximately 10cm per second. This ensures an even, atomised coating of the internal surfaces where moisture often sits undetected. Repeat for all cross-members and subframes.

Remove the interior door cards or use the drain holes at the bottom of the doors. Carefully spray cavity wax into the bottom 10cm of the door internals. This is a primary fail point in coastal areas where salt air enters through window seals and condenses inside the door. Ensure you do not block the actual drain holes; use a small pipe cleaner to clear them after spraying.

In temperatures below 25°C, lanolin can become thick. For the best atomisation, place your lanolin containers in a bucket of warm water (approx 40°C) for 20 minutes before application. This lowers the viscosity, allowing the product to 'creep' into tight welds and laps more effectively. Do not use a microwave or open flame as the carriers can be flammable.

Using a professional spray gun (set to 40-60 PSI), apply a heavy 'wet' coat of lanolin to the entire undercarriage. Work from the front of the vehicle to the back. Cover the chassis rails, floor pans, suspension arms (avoiding bushings), and the back of the differential. The coating should look glossy and slightly thick, but not so heavy that it is running off in large streams.

Pay extra attention to where two pieces of metal are joined or welded. These areas are prone to 'crevice corrosion.' Hold the spray gun closer (15cm) to these joints to force the product into the gap. The capillary action of high-quality lanolin will draw the oil into the seam, displacing any residual oxygen or moisture.

One of the benefits of lanolin is its dielectric property. Lightly mist electrical plugs and ground points on the chassis. This prevents 'green rot' (copper oxidation) in the wiring harness, which is common in vehicles exposed to beach work or heavy river crossings. Do not saturate, a light film is sufficient for moisture displacement.

Remove the plastic inner wheel liners if possible. Spray the metal behind these liners heavily. Road debris kicked up by tyres acts like sandpaper, constantly eroding factory protection. A thick layer of lanolin here provides a sacrificial 'soft' barrier that absorbs the impact of sand and small stones, preventing them from chipping the paint.

Often overlooked, the spare tyre winch and mounting bracket are prime candidates for seizing due to rust. Thoroughly coat the mechanism and the cable. If you have a front-mounted recovery winch, lightly mist the mounting cradle and the underside of the winch housing to prevent corrosion between the dissimilar metals of the winch and the bullbar.

Use a high-lumen LED torch to inspect the entire underbody. Look for 'shadows' or dry spots where the spray pattern missed. Common missed spots include the top side of the chassis rails and the area above the fuel tank. Apply a second light coat to these areas to ensure 100% coverage. The underbody should have a uniform, waxy appearance.

Allow the vehicle to sit for at least 2 hours before moving it. This allows the solvent carriers to evaporate, leaving behind the protective wax/oil film. Use a rag dampened with mineral spirits to clean any overspray from the exterior paintwork or chrome. Remove the masking foil from the exhaust and brakes. Do not drive on dusty roads for at least 24 hours to allow the coating to set.