Wash every one to two weeks through a Colorado winter and always within a few days of driving through a treated storm, because de-icer keeps working on the car long after the road has dried. The interval matters far more than the technique.

Why the interval is the whole answer

Magnesium chloride, the liquid de-icer Colorado sprays on its roads, is hygroscopic. It pulls moisture from the air and holds it against metal, so a salted car sitting in a dry garage is still corroding.

That is the difference from rock salt, which dries out and flakes off. Mag chloride film stays active until it is physically rinsed away.

A fortnightly rinse done badly beats a perfect wash done in March.

The part most washes miss

The undercarriage is where the corrosion actually starts, and a standard wash does not reach it. Brake lines, fuel lines, subframes, fasteners and the inside of the sills all take road spray directly and none of them are painted to the standard the panels are.

If you only do one thing differently this winter, add an undercarriage flush.

Rinse before you touch it

Dry salt and grit are abrasive. Wiping a mitt across a dirty winter panel is sanding, and it is where a lot of swirl marks come from. Rinse the panel thoroughly before any contact.

This is also why brush washes are worse in winter than any other time of year. The brushes are carrying grit and salt from every car ahead of you.

Temperature matters

Wash when it is above freezing, and dry the door shuts, seals and locks afterwards. Washing at 20 degrees leaves water in the door seals that freezes them shut overnight, and forcing a frozen seal tears it.

If it will not get above freezing for a week, a rinse on the warmest afternoon available still beats waiting.

What makes it easier

Two things cut the effort enough that the interval actually holds.

A ceramic coating at $299 stops most of the salt film bonding in the first place, so a winter rinse becomes water and a few minutes rather than a fight. It does not remove the need to wash, it removes the reason people skip it.

Monthly maintenance at $130 exists for the same reason. Almost everyone knows they should wash the car in February. Very few do it. The plan is the interval, kept by somebody else.

The winter routine, short version

The whole winter routine is six habits, and the first two matter more than the rest put together.

Every one to two weeks, November to April
Always within a few days of a treated storm
Flush the undercarriage every time
Rinse before any contact with the paint
Wash above freezing, dry the seals and shuts
No brush washes

We work off the truck with our own water and power, which in January is the difference between washing the car and finding the outside tap frozen solid. We cover 25 miles from Broomfield.