First, moisture and carbon dioxide in the air mix to create a weak acid that starts to dissolve the iron. Think about how easy it is to crumble a flake of rust between your fingers, and then imagine that stuff trying to protect you and your loved ones during a car crash.
A stray piece of gravel or a minor fender bender is all it takes to chip a car ’s paint, and any iron in the body panels will start to rust as soon as air and water reach the metal beneath it. That means rust spots can be fairly common on used vehicles, particularly if they’ve been driven in a northern U.S. state that uses chemicals and salt to device winter roads.
But if the rusting process goes on too long, it can eat right through the metal, causing holes and allowing body panels to fall to pieces. This is where problems go from cosmetic to dangerous, because modern cars and SUVs rely on these body panels for their structural integrity.
The most serious problems occur when rust gets beneath the car ’s surface and within its underlying components. Rust -free body panels boost a vehicle’s structural integrity, but the parts doing the heavy lifting lie under the car ’s skin.
Unfortunately, this area of a vehicle is often susceptible to rust -causing chemicals and water, which can accumulate there when a car drives down wet or icy roads. Most customers should avoid used vehicles that show strong signs of structural rust.
CARFAX also recommends getting an expert inspection that includes putting the vehicle up on a lift, to give your mechanic a better view of under body components. You can apply touch-up paint to stone chips, small scratches, and other minor nicks and dings, but truly repairing rust can take several steps, a variety of tools and materials, and quite a bit of skill.
Depending on the size and severity of the rust, blending the repaired area with the surrounding paint may require wet sanding or buffing the surface. Dirt can retain and trap moisture, and road salt, bird droppings, and other corrosive materials will eat away at paint if they’re left unattended on metal surfaces for long periods.
Waxing it on a regular basis (twice or more each year) will add a protective surface to the paint and clear coat. Wash and wax more frequently if you live near an ocean or in an area where highway crews spread salt on the roads to melt snow and ice during the winter.
Also, frequently check the fender liners and other areas under the hood, along the sides of the engine bay, for any standing water. Check the trunk or cargo area to make sure water isn’t seeping past the seals.
Stone chips and other nicks and dings that are left unrepaired can develop into rust spots over time, so it pays to buy some matching touch-paint to cover those imperfections. Corrosion is a daily hazard for millions of American drivers, but it doesn’t have to be a death sentence for your car or truck.
Over time, as these areas stay almost constantly wet, that trapped water will wreak havoc on the metal of your vehicle. Salt speeds up the electrolytic reaction that occurs between iron and oxygen in the presence of water, so a wet and salty undercarriage during the winter months is at an even higher risk of rusting out.
You can help keep things free of corrosion by adding your own light covering of oil or undercoating, which will cling to the metal and repel water. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.
I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry. The most serious problems occur when rust gets beneath the car ’s surface and within its underlying components.
Given enough time, oxygen, and water, any iron mass will eventually completely rust and disintegrate. Body shops can easily remove the rust if they have the tools and equipment to do the job right.
Fortunately, there are a number of things you can do to stop rust from eating into the metal. A piece of iron which is immersed in oil will take more time to corrode than two of the conditions described above.
And even the best efforts sometimes fail to make a long-term rust repair last longer than six months. The subframe usually braces integral parts of the car, such as drivetrain, suspension or engine.
Once it has been removed from the vehicle, holes caused by metal corrosion can be treated. There are much fiberglass tape and filler kits available to help you patch subframes that have rusted through.
When the two substances come into contact with each other, it causes an atomic reaction that results in oxidation. A rusted frame will be a major safety hazard if the corrosion is bad enough.
… After assessing structural integrity, they’ll tell you whether an expert welding job could fix the frame or whether you’d be better off just selling the car for scrap. During the first stage of rust, red, black, or white deposits become noticeable on the surface of the metal.
Apply to fabric and rub with a damp cloth, then rinse before washing. Or rub toothpaste onto rust marks on silverware or tools, let sit for 10 minutes, then wash away.
If your car is suffering from rust holes, it’s probably not worth doing much cosmetic repair. The biggest advantage of undercoating products is the protection against corrosion for longer periods of time.
Most of them can last for up to 10 years or more, which helps reduce rust and thus extends the lifespan of your vehicle. As a general rule of thumb, it’s important to wash your car at least every two weeks.
And it’s not just the structure; rust can corrode various parts, rendering them useless unless completely replaced. Unfortunately, rust issues aren’t confined to cars from one certain manufacturer or age group.
One major determinant of a car ’s likelihood for rusting is its geographical location. Rust problems are more common in humid climates and in areas where road crews use salt to keep ice off the streets during the winter.
Areas such as the Upper Midwest and parts of the Northeast are especially known for rusting vehicles, largely because they suffer from both humidity and heavy road-salt use. But just because you’re located in an area that isn’t known for humidity or salt use doesn’t mean you’re safe from rust.
Common rust spots include the frame rails, which run underneath a car ’s doors on each side, the wheel wells, the exhaust, the suspension and virtually any other underside components made of steel or metal. Once you have the car back on the ground, pull up the trunk carpeting and check for any signs of rust.
While we generally suggest consulting a professional about these issues, you can usually remove rust spots by sanding them away, so they don’t become worse and create further problems with your car. I spotted some rust on the underside of the car between the back wheels.
By the time the inspection was completed (and failed), I had a hole in my muffler system along with about $2,500 worth of rust related repairs for a $1000 vehicle. However, to check you're going to have to do the squeeze test between fingers and thumb on the thicker structural sections, then if you still can't determine how severe or not the rust is. It's time to get an old screwdriver out and tap (with the handle part) on the rustiest bits.
If the material is corroded right through holes will likely appear, this is not good especially in the structural sections, if this is the case then you may like to walk away from this one as welding will be required. If however it is just surface rust then a scrap off and clean up followed by an application of under body protection will suffice and your good to go.
The seller should have no issues at all with you taping on the structural parts of the body to check its integrity. In some parts of the world where lots of salt is used in the winter, this is not unusual rust.
If you want to keep it longer term, I'd treat the rusty areas on the under body with a wire wheel brush on an angle grinder, rust converter and fresh undercoating after a thorough clean.