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Underbody car wash
Short answer: an underbody (undercarriage) wash sprays the underside of the car from below to rinse off road salt, brine and grime. In a Canadian winter it matters more than anything that happens to the paint: get one every one to two weeks while the roads are salted, and a thorough one in spring.
What an underbody wash does
In an automatic or tunnel wash, the underbody option runs a set of nozzles or a spray bar in the floor. As the car passes over them, high-pressure water — sometimes with a rust inhibitor or detergent — hits the floor pan, the subframe, the suspension and the insides of the wheel wells. Some programs call it undercarriage, chassis or underbody wash; the idea is the same.
At a self-serve bay you do it yourself with the wand: crouch at each wheel and aim into the wheel well, then along the sills and under the bumpers, from every side of the car. It takes longer, but you control where the water goes.
Why the underside matters in Canada
Road crews across most of the country spread rock salt and spray brine to keep roads open. The salt water splashes up and sticks to the underside of your car, where it stays damp, dries into a crust, gets wet again with the next slush and keeps working. Steel parts underneath are the ones that suffer:
- brake lines and fuel lines,
- the subframe and suspension components,
- the exhaust,
- rocker panels, the bottom edges of the doors and the wheel arches.
Dirt on the paint is cosmetic. Salt on the underside is what leads to rust on parts you cannot see until a mechanic shows you. Our winter car wash guide covers the rest of the salt season.
How often
- Every one to two weeks while the roads are white with salt.
- After every big storm, once the roads have dried — that is when the most salt is on the car and not on the road.
- One thorough wash in spring once the salt season ends, ideally with a close look into the wheel wells.
If that many washes add up, a monthly membership that includes the underbody program can be cheaper than paying each time — do the maths for your wash.
Choosing the right program
At many automatic washes, the underbody spray is not in the cheapest program. Read the board before you pay. In winter it is worth dropping extras like tire shine or a triple-foam wax in favour of the program with the underbody rinse. Both touchless and soft-touch washes can have it — whether the program rinses the underside matters more than how the top is cleaned. We compare the two in touchless vs soft-touch.
Cold days
Below freezing, water on the underside and in the brakes can freeze once you drive off. Pick a wash with a dryer, drive a few minutes and brake gently to dry the brakes, and wipe the door seals. On very cold days, waiting for a milder one is fine — a few days more matter less than rinsing regularly over the whole season.
Rust protection and the underbody wash
Many Canadian drivers have an oil-based rust protection sprayed on every year. It works best on a clean underside, so an underbody wash before the application is a good idea. Afterwards, ask the company that applied it how and when they recommend washing — practices differ between products. Rustproofing and washing are not either/or: the coating slows corrosion, the rinse removes the salt that feeds it.
Where to find one
Our map covers 5,780 car washes in Canada, including 778 touchless and 953 self-serve washes. Find a car wash near you and check its programs for the underbody option.
Questions
Is an underbody car wash worth it?
In a Canadian salt season, yes. Salt and brine collect on brake and fuel lines, the subframe, suspension parts, wheel wells and rocker panels — the places a normal wash misses and where rust starts.
How often should you get an underbody wash in winter?
Every one to two weeks while roads are salted, and after major storms once the roads have dried. Finish the season with one thorough underbody wash in spring.
Does an underbody wash remove rust protection?
A normal underbody rinse is designed to remove salt and dirt. Oil-based rust protection sprays can wear off over time with washing and driving, which is why they are reapplied regularly. Ask the company that applied yours how they recommend washing.
Do all automatic car washes have an underbody spray?
No, and where they do, it is often only in the mid-priced or top programs. Read the program board before you pay; the option is usually called undercarriage, underbody or chassis wash.