Keeping the Rust at Bay: Protecting Your Vehicle's Undercarriage

Don't do this on your nice decorative driveway. The grease and red dust will stain it forever. Use the grass or a dedicated wash bay at a servo if you have to.

Spraying cold water on a boiling hot exhaust or engine block is a recipe for cracked manifolds. Give it at least an hour to cool down.

If you've got a lifted 4x4, you might be fine on the ground, but for most cars, getting it up on ramps gives you the clearance you need to do a proper job. Just make sure the handbrake is on and the wheels are chocked.

Start by hitting the whole underside with just water. You're looking to knock off the loose stuff. Focus on the wheel arches and the inside of the chassis rails where the mud likes to hide.

Chuck your degreaser into a foam cannon or a pump sprayer. Coat everything, the suspension components, the drivetrain, and the frame. Avoid the brake rotors if you can, though a bit won't hurt if you rinse it well.

Let it sit for about 5-10 minutes. Don't let it dry out! If it's a 40-degree day, you'll need to work in sections.

Get in there with your nylon brush. I once saw a guy try to use a wire brush on a modern chassis, don't do that. It strips the factory e-coat. Stick to nylon to agitate the grease and red dust.

This is the most important part. Use the underbody attachment if you have one. You want to keep rinsing until the water runs clear. If you've been in the red dirt, this might take a while.

Most chassis rails have small drain holes. If these are blocked with silt, your frame will rust from the inside out. Use a small screwdriver or a zip tie to poke them clear.

You can't apply protection to a soaking wet surface. If you've got a leaf blower, use it to blast water out of the crevices. Otherwise, leave it in the sun for a few hours.

Look for 'tea staining' or bubbling paint. If you see light surface rust, hit it with a rust converter before you seal it up. If it's crunchy, you've got bigger problems.

My preference is a Lanolin-based spray like Lanotec. It's derived from sheep's wool, it's non-toxic, and it doesn't dry hard, so it doesn't crack. Spray a generous coat over the frame, suspension arms, and bolts.

You don't want it dripping everywhere. Give it a light wipe with a rag to ensure an even coat. Be careful not to get any on your exhaust, it'll smell like a burnt sheep for a week if you do.

Before you finish, hit your brake rotors with some dedicated brake cleaner to make sure no overspray from the protective coating landed on them.

Take a light and look for any spots you missed. Usually, it's the top side of the fuel tank or behind the spare tyre.