Chicago winter reality: salt doesn’t just live on the paint
I’m Brian O’Connor, based in Chicago, and by late January you can practically taste the brine in the air when_limitless traffic crawls along I-90. Road salt (and increasingly, liquid brine) is effective at melting ice, but it’s also an electrolyte. Add moisture and oxygen and you’ve built a little corrosion lab under your car. Theees that matter aren’t always the obvious ones on the rocker panels rust usually starts where salty slush sits, dries, then gets rewetted over and over.
Where rust starts first (the spots people don’t look)
Wheel-arch edges and liners: The lip of the fender and the rear quarter panel edge catch sandblasted grit. Mud and salt pack behind plastic liners, especially where clips or screws leave tiny gaps. You can’t see it until a bubble shows up, and by then it’s been working for a while.
Sills/rockers (pinch welds and seams): The rocker area is a stack of folded steel seams. Those folds trap moisture. If you use a floor jack on a salty pinch weld, you can chip coatings and start a problem you won’t notice until spring.
Subframes, suspension arms, and fasteners: Most modern vehicles use coated steel and e-coat processes that hold up well, but the first failures are often at edges, bolt heads, and stamped corners anywhere the coating is thin or gets nicked by debris. The mild annoyance here: once hardware crusts over, future alignments or shock replacements get slower and more expensive.
Brake lines and fuel lines: Lines run along the underbody where slush collects. Many vehicles use corrosion-resistant materials or coatings, but even then, clamps and brackets can become the weak link. If you live in the Rust Belt, this is one of the few areas that can become a safety issue if neglected long enough.
Door drains and hatch drains: Doors are designed to get wet inside; they rely on drain holes at the bottom. Salt-laden water plus clogged drains equals standing water. That’s when you get rusty seams at the lower door edge often mistaken for “bad paint.”
The “no-frenzy” rinse checklist (fast, repeatable, actually helps)
You don’t need a detailer’s ritual. You need a consistent rinse that targets salt traps without forcing water into places it doesn’t belong.
1) Start with the underbody gently. Use an undercarriage rinse if your local wash offers it, or a hose with a sprinkler-style underbody attachment at home. Focus on: behind the front wheels (subframe area), along the rocker pinch welds, and over the rear suspension cradle. Keep pressure moderate; you’re dissolving salt, not stripping coatings.
2) Wheel wells: rinse, then flush behind the liner edges. Turn the front wheels full lock and rinse the liner seams where they meet metal. Rear arches matter even more on many cars because they collect grime like a shelf. If you hear grit pinging off plastic as you rinse, that’s normal and satisfying.
3) Rocker panels and lower doors: sheet water downward. Let water run down from above rather than blasting upward into seams. Then confirm door drains are open: look for small slots/holes along the bottom edge of each door and make sure water can exit freely.
4) Avoid spraying directly into connectors and vents. Don’t aim high-pressure water at visible electrical connectors under the hood or along exposed harnesses under the car. Also avoid blasting directly into exhaust tips (especially when cold) or any visible cabin pressure vents near the rear bumper area; these are designed to breathe, not to be pressure-washed.
5) Skip harsh chemicals on bare metal bits. Strong degreasers can strip protective films from certain components. Plain water does most of the work for salt removal. If you use soap, keep it mild and rinse thoroughly.
When to wash and what to do right after
The best time is when temperatures are safely above freezing so water can drain instead of turning into ice inside crevices. After rinsing, take a 10–15 minute drive. The brakes will dry with light use (you’ll feel them bite normally again), and airflow helps evaporate water from wheel wells and seams. Parking immediately in an unheated garage can trap moisture; if that’s your only option, at least do the drive first so you’re not sealing in slush.
A quick inspection every 2–3 weeks (two minutes, no lift required)
Crouch by each wheel arch and look at the lip for packed debris. Run a finger along the rocker pinch weld (carefully) to feel for heavy crusting. Peek under the car with a flashlight: check brake lines where they run along brackets, and look for wet dirt stuck on subframe corners. Finally, open each door and confirm drains aren’t blocked. It’s not glamorous work but in Chicago winters, it’s one of the few habits that pays you back quietly for years.