Rust — as any Neil Young fan knows — never sleeps. There are a lot of things you can do to keep it at bay, though, and get your car through the coming winter unscathed. These options run from the nearly-free to about $1,000 to perform:
Now that manufacturers have 100,000-mile outer body rust through warranties, you’d think that rust wasn’t a problem anymore, but just ask the owners of TJ-era Jeep Wranglers or the 150,000 2001 to 2004 Toyota Tacoma owners that had their trucks rust out from underneath them. Nissan Altima owners are also experiencing floors that completely rust out of the cars.
There are preventative measures you can take to slow the oxidation of even the most fragile cars and trucks, though.
Clean Your Drains
Every single car has drains in various locations. They’re designed to keep water from collecting in places that are prone to rust. When drain holes get plugged with leaves, dirt and pine needles, they do exactly the opposite of the job they’re supposed to do, to the point that you’ll start to hear water sloshing around inside of doors and fenders.
You’ll have to find the drains in your specific car, but they’re usually along the bottom of the doors, in the floors, at the bottoms of fenders, and in the tailgate.
Pay attention to the drains in your sunroof, too. They’re usually at the forward corners. As AAA Car Doctor John Paul mentioned, Ford Escape owners have had issues with the forward edge of the sunroof opening rusting out because the drains get plugged.
Wash Your Car
Automakers have made great strides in galvanizing sheetmetal, but eventually dirt, mud, sand and salt will all conspire to wear away whatever protective finish is on your car. Your best defense is to keep the car clean.
We’re not suggesting you go outside and blast the car off with a hose in the middle of February. It’s uncomfortable, and frankly, with water restrictions the way they are now, it’s probably illegal in most communities.
There’s nothing wrong with a car wash, but we like the touch-free variety that use high-pressure water instead of cloth that can trap dirt and do more harm to the car’s finish than good.
Most decent car washes have an undercarriage wash as an option. For the extra two bucks, it’s well worth it to blast some warm water in the crevices of the car that you never see.
Try to hit the car wash once every couple of weeks, or after the roads have gone down to bare pavement. It will add decades to the life of your car.
Don’t Forget the Inside
On the inside, the moisture and salt you track inside the car can leach through the carpets and sound deadening material to rust out the floor from the inside. Invest in a decent set of rubber floor mats that protect the floors from all that water and sodium or calcium chloride, and vacuum the interior regularly to keep sand from working its way through the carpet to the steel floor below.
The bonus is that you’ll enjoy a clean car all winter, rather than one that’s littered with Ding Dong wrappers and YooHoo bottles.
Oil Undercoating
There are still Vermont farmers driving around with trucks from the 1960s and 1970s that have survived decades of New England winters. It’s because they undercoat their trucks with oil. Old-timers would pressure-wash the underside of their trucks, fill up a Hudson sprayer with waste oil they’d drained out of their equipment the rest of the year, and coat the underbody with atomized oil, spraying inside doors, fenders and frame rails.
It’s the messiest job in the world, though, and probably not environmentally friendly. Smarter folks have been using bar and chain oil for chainsaws. It’s economical at about $5 a gallon, and it’s also got some adhesive properties so that it’ll stick to whatever you shoot it at, leaving behind a thin film of oil, rather than a drippy mess.
Oil Undercoating II
If you’re lucky enough to have somebody close by who does it, there are companies around that will oil undercoat your car or truck for you. Oil Undercoating of NH, for example, will oil undercoat most cars and trucks for between $159 and $169, depending on the size and complexity of the job.
Waxoyl
There is nothing that ever rusted like a British car. For 55 years, Brits in the know protected their cars with a product called Waxoyl. Unlike oil that can be eventually washed away from some surfaces, Waxoyl is a wax product that hardens and adheres to the underbody.
You can buy Waxoyl from some suppliers, but find a trained shop to apply it for you. BDR Automotive in Holliston, Massachusetts, for example, has the applicator wands that reach deep inside door panels and frame rails and spray 360 degrees at the end to ensure maximum coverage. 
Waxoyl comes in two formulas: Waxoyl 120-4 is used for inside of door panels and other crevices. Where rust has already formed, Waxoyl 120-4 stops metal from corroding further. Waxoyl Hardwax forms a tough, flexible wax barrier on the car’s undercarriage.
