What You'll Learn
Aussie Conditions
Look, if you're living near the coast or planning a big trip up the Cape, underbody rust is your biggest enemy. We get some of the harshest conditions in the world here, and once that brown rot starts, it's a nightmare to stop. This guide is for anyone who wants to keep their chassis mint, whether you've got a brand new 300 Series or an old Hilux you're trying to keep alive. I'll walk you through how I do it in my shop so you don't have to pay a pro two grand to do the same thing.
Why Rust is Chewing Your Car Faster Than You Think
The Gear You'll Need
What You'll Need
While you're here...
Getting the Gunk Off First
The Deep Clean
You can't protect over mud. Give the underbody a massive wash. Spend at least 20 minutes just flushing the frame rails. If you've been in red dust, you'll be amazed how much keeps coming out.
Degrease and Salt Neutralize
Spray your salt remover or degreaser everywhere. Let it dwell for 10 minutes (don't let it dry in 40 degree heat though!) and scrub the heavy bits. This breaks the ionic bond salt has with your metal.
Dry Time
This is crucial. You cannot spray a sealant on a wet chassis. Leave it in the sun for a few hours. I usually do the wash in the morning, go have a pie and a brew, and come back when it's bone dry.
The Protection Process
Inspect for Existing Rust
Get under there with a bright torch. Look at the welds and the sharp edges, that's where it starts. If you see flaky brown stuff, we need to deal with it now.
Mechanical Descaling
Take your wire brush to any surface rust. You don't need it back to shiny chrome, but you need the loose flakes gone. If it's a black Commodore or something similar, be careful not to scratch the visible paintwork.
Apply Rust Converter
Dab your converter onto the raw spots. It'll turn the rust black. Let it cure for the time on the bottle (usually a couple of hours). This stops the chemical reaction of the rust.
Masking Off
Don't be lazy here. Chuck some plastic or newspaper over your brake rotors and the exhaust manifold. You do NOT want lanolin on your brakes, and you don't want it burning off your exhaust for a week.
First Pass, Inner Rails
If you're using a spray can with a straw, poke it into every hole in the chassis rail. Spray as you pull it out slowly. This is the most important part because rust starts from the inside out.
The 'Hidden' Spots
Pay attention to the top of the fuel tank, the spring perches, and behind the wheel arch liners. These are the spots mud sits in and rots while you aren't looking.
Main Underbody Coat
Spray a consistent layer over the entire chassis and floor pan. I reckon a 'wet' look is what you're after, but it doesn't need to be dripping off onto the driveway.
Differential and Axles
Give the diff housings and axles a good coat. Avoid the rubber boots on the CV joints if you can, some oil-based products can make the rubber swell over time.
Spare Tyre Winch
A mate of mine once got a flat in the middle of the Simpson and his spare tyre winch was rusted solid. Took him three hours to get the spare down. Spray the winch mechanism well!
Wipe Down Over-spray
Check your side steps and lower door plastics. Give them a wipe with a microfibre so they don't attract every bit of dust on the road the second you drive off.
Watch Out
The Heat Factor
Watch Out
Keeping the Protection Working
Common Questions from the Shed
Will this make my car smell like a sheep?
Can I just use old engine oil?
What if I've already got electronic rust protection?
How many cans do I need for a dual-cab ute?
Trusted by 50,000+ Aussie car owners
Professional advice for Australian conditions
Products We Recommend
Keep Learning
Ready to level up your car care?
You've got the knowledge—now put it into action. Explore more guides or check out our recommended products.
Get Weekly Car Care Tips
Join 12,000+ Aussie car enthusiasts
Keep Reading
Keeping the Rust at Bay: Protecting Your Vehicle's Undercarriage
Most people spend hours waxing the paint but completely ignore the most vulnerable part of their car. If you're hitting the beach or driving through red dust, your undercarriage is taking a beating every single day.
Post-Beach Salt and Sand Removal
Driving on the sand is a blast, but the salt will eat your chassis alive if you're lazy. Here is exactly how to flush the muck out and save your paint from the Aussie sun.
How to Properly De-Salt Your Rig After a Beach Trip (Mar 2026)
Driving on the sand is the best part of owning a 4x4, but the salt will eat your chassis alive if you aren't careful. Here is how to get every bit of grit and brine off before it turns into rust.
Keeping the Rust Off: Your Underbody Protection Checklist (Mar 2026)
Don't let the salt and red dust eat your chassis from the inside out. This checklist covers exactly what you need to inspect, clean, and protect to keep your rig rust-free for years.