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I live in an area that gets a fair amount of snow and ice, and so the winter months usually have salt on the roads. Presumably, that salt stays around as a dry crust or in puddles until the next heavy rain washes it off. And as most of us know, salt greatly accelerates rust.

So, having spent almost $1000 this winter on rust repair and prevention (replacing a good chunk of frame that was almost completely gone, and then cleaning and coating everything), I'm wondering about how to keep the salt off. Of course, the easiest way is to have a second, sacrificial vehicle for this and not drive the good one, but unfortunately, that's not an option right now.

My two conflicting theories at the moment are:

  1. Hit a carwash often, mostly to blast the underside with freshwater. This carries the salt away...but then it gets right back on as I drive home.
    Also possible for water to get into a crack somewhere and freeze before it evaporates?
  2. Don't wash it, but let the salt dry in place. It needs moisture to work, and so that dry layer can offer a small (perhaps false?) amount of protection if it's allowed to stay on. Also avoid driving through puddles or wet spots as much as possible, as that provides the moisture to start working again.
    Then hit the carwash once, as soon as a good rain has washed the salt off the roads.

What do you guys think? Merits or drawbacks that I didn't mention? Am I all wet on both counts?

  • I've seen automotive owners manuals that specifically recommend washing the bottom of cars operated in salty environments to avoid excess corrosion. It didn't say what time of year, but I remember one mentioned that it should be done twice a year. – Tim Nevins Jan 29 at 22:32
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I wash my vehicles whenever the temperature gets high enough to be able to do so during winter. A film of dried salt on sound paintwork or the e-coating on the frame won't do much damage, but wherever it can get to metal through porosity of or damage to the coating will initiate corrosion - which then creeps under the paint.

What salt is used on roads varies by region, and it's often not just rock salt (sodium chloride) that's used these days, since that tends to dry, get powdered and blow away from the road surface, so magnesium and particularly calcium chloride are often used as well. These are more expensive, but can be used in smaller quantities since they're fairly tenacious - and that includes remaining on your vehicle. These salts are hygroscopic - if there's any moisture in the air, they'll absorb it, leaving a concentrated brine. The effect on metal structures, such as iron bridges, and even rebar in concrete is beginning to become obvious in regions that use this.

First line of defense would be ensuring there's a continuous protective layer over the vehicle structure of either paint and/or a waxy protectant, and washing salt off as much off as possible, whenever possible.

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    I didn't think about using different chemistries that are hygroscopic. That kinda blows away the "dry protective film" idea. – AaronD Jan 28 at 17:51
  • Plus, a clean car is so much nicer to work on, no matter the season)! – Bob Cross Jan 30 at 14:22
  • You should definitely wash your vehicle at least twice a month. It will help remove salt and road grime buildup, and keep your car from developing rust spots. – CalgaryCoolCat Jan 31 at 22:04
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Wash it, got to be better than leaving salty wet dirt in contact with metal.

Also make sure metal surfaces are clean, primed and painted - both sides...

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  • I already rebutted that in the original question. More detail please? – AaronD Jan 28 at 17:48
  • Dry Salt continues to corrode from the moisture in the air. Best to remove it. – Moab Jan 28 at 17:50
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The trick is, before the snowy season, drive as many dirt roads as you can and never wash your car. This builds a patina of dirt that the salt can't get through. This strategy works best if you have a brown car to begin with. It worked just fine with my '87 LeBaron. The engine died well before it rusted through.

Just kidding. Do as Phil G. says; wash and wax often.

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