As cars age, one of their biggest enemies is rust. A little rust on a car’s body is common, and it is not a big deal if caught early and fixed. However, if it gets into a vehicle’s frame, it can become a safety issue. If rust compromises a vehicle’s structure, there could be a catastrophic failure in even routine driving. The key is knowing how much rust is too much, and what you can do in preventing rust on your classic car or truck.
What Is Rust?
Rust is the combination of iron and oxygen, also known as iron oxide. It is created as the result of the chemical reaction when iron (or alloys containing iron, like steel) is exposed to water and air over time.
First, moisture and carbon dioxide in the air mix to create a weak acid that starts to dissolve iron. At the same time, some of the water is being broken down into its separate elements – hydrogen and oxygen. As those oxygen atoms meet and bond with iron atoms, the result is iron oxide.
Road salt and other products used to melt ice can speed up this chemical reaction on a car’s undercarriage or in other exposed areas.
Why Are Cars Rusty?
Rust forms because of the electrochemical breakdown of iron-based metals. This breakdown is the result of oxidation, which is the process where iron surface molecules react with oxygen in the environment and produce a new molecule, Fe2O3, otherwise known as iron oxide. That iron oxide is rust.
Pure iron does not oxidize as aggressively. Examine an old iron engine block and you will see a thin surface layer of rust but little penetration into the metal. Unfortunately, iron alone is not a particularly good material for building cars, so today’s cars typically use steel alloys. Adding a dollop of carbon to iron creates steel, which offers dramatic improvements in flexibility, tensile strength, and formability. However, this added strength comes at a cost, as it adds impurities that accelerate the formation of rust.
Exposed steel rusts at different rates depending on several factors: alloy components, thickness, the environment the steel lives in, and the type of heat treating the steel undergoes. Very poorly made cars in the 1970s began showing surface rust as soon as they hit the docks. Completely untreated raw sheet steel can rust through in as little as a few years.
Why Is Rust Bad for Your Car?
Why is rust a danger? Because, despite iron’s impressive strength, iron oxide is exceedingly brittle. 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.
Most modern-day cars are engineered with extensive anti-rusting measures thus preventing rust, including clear-coat paint finishes that protect both the paint and body panels, as well as galvanized coatings that shield a vehicle’s steel body structure. Many of these materials do not exist on vintage cars.
Additionally, automakers are moving away from rust-prone iron-based metals to more rust-resistant surfaces such as aluminum and carbon fiber. These materials may have their own issues, but because they do not contain iron, rust will not be one of them.
Types of Car Rust
Surface Rust
A stray piece of gravel or a minor fender bender can chip a car’s paint, exposing the bare metal beneath. Any iron in the body panels will start to rust as soon as air and water reach it.
Because of that, rust spots are common on used cars, particularly if they have been driven in a northern U.S. state where chemicals and salt are used to de-ice winter roads.
Now, these spots should not necessarily be deal-breakers since they are inexpensive to repair. The rust can simply be sanded off, painted, and given a clear-coat finish to seal out the elements.
But if the rusting process has gone on too long, it reaches the stage at which it begins to flake. This is called scale rust, and if it continues, this penetrating rust will eat right through the metal, creating holes and leaving body panels to fall to pieces. At that point, problems go from cosmetic to dangerous, because cars rely on these body panels for their structural integrity.
Surface rust is not limited to the parts of a vehicle you can see. Exposed areas underneath a car are potential sites for rust.
Structural Rust
The most serious problems occur when rust gets beneath the car’s surface and within its underlying components – those parts doing the heavy lifting lie under the car’s skin. Unfortunately, this area is a prime location for rust. Rust only needs a tiny crack in a car’s frame to begin its work.
If there has been damage to a car’s body structure, make sure it is repaired correctly. If not, you could find yourself in a vulnerable situation during an accident. Most customers should avoid used vehicles that show strong signs of structural rust but discovering those signs can be tricky.
Steps To Preventing Rust
There are steps you can take to prevent rust from forming on your car. From a simple wash and wax to paint touchups and leak checks, here are simple steps that will minimize your car’s rust risk:
Wash and Wax Your Car Regularly
The best way to prevent rust is the easiest: Wash and wax your car often.
Dirt can retain and trap moisture, and road salt, bird droppings, and other corrosive materials will eat away at paint if they are left unattended.
Washing your car frequently will remove these corrosive materials. 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. Salt is Public Enemy No. 1 when it comes to rust prevention.
Wash the Underside of Your Car
Many car washes offer an underbody spray that can help remove salt, dirt, and grime from critical areas you cannot easily see, such as the frame, suspension components, and wheel wells. These are all prime breeding grounds for rust.
Keep Your Car’s Drain Holes Clear
The drain holes are located on the bottoms of doors and on the rocker panels (the area below the doors); keeping them will not let water accumulate and cause rust. This problem is particularly acute on minivans and large vans. Use a coat hanger or pipe cleaner to make sure the holes remain open.
Check for Water Leaks
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 is not seeping past the seals.
Stay on Top of Paint Chips and Dings
Stone chips and other nicks and dings that are left unrepaired often develop into rust spots over time, so it pays to buy some matching paint to cover these imperfections.
Dealing With Those Hidden Areas
The not-so-obvious advice is to check the drain holes along the bottoms of doors and rocker panels, which allow rainwater to flow out. Use a pipe cleaner to clear these holes out and keep the car’s nooks and crannies dry. WD-40 can be a useful tool here as well. This lubricant protects parts from corrosion, and its thin nozzle can be used to reach tight underbody spots and blast away water or corrosive grime.
As noted earlier, many cars and trucks have a thick coating on the underside that chemically seals the steel against oxidizing agents. Regular inspection and repair of the spots that have worn bare will keep rust from advancing and causing additional damage. If this coating is not there, consider adding one yourself. POR-15 is one of the more popular examples of such a rust-protective sealant, and they even have a rubberized coating to go over it in case you want even more protection underneath your car. As with other rust repairs, sand off any rust that might be sticking through and rough up the area you intend to paint with some sandpaper, then brush or spray the new coating on.
If your metal is properly sealed from the elements and kept clean of corrosive salt and grime, you should be able to get years of safe driving out of even the most abused winter beater.
Finally
An ominous brown stain on the fender. A bubble in the paint at the bottom of a door. Soaked floors after hitting a puddle. These are signs the iron worm has been hard at work: rust.
Otherwise, fine cars are routinely sent to early graves because they become rusty cars, even though it is an avoidable problem. With iron-based metals, battling oxidation can feel like a Sisyphean task. Despite the advanced coatings and alloys developed by chemists and engineers, iron’s unstable chemical makeup means it will always succumb to rust in a natural environment. In fact, iron and most steel will completely reduce to iron oxide and other constituent elements over a long enough time.
This does not mean that your car is doomed for the scrapyard! Understanding how cars become rusty, your car’s problem areas, and how car rust can be repaired from that brown, flaky trouble means that your pride and joy can stay on the road if you do. Preventing rust will go a long way toward keeping your classic car in top condition.
I have a friend who restores cars. He swears removing for panels and spraying oil inside the doors and getting it in the seams helps. Not just doors anywhere you can get oil helps. I imagine small drilled holes could help access place then be plugged.
Used engine oil has contamination which can promote rust. Clean engine oil isn’t that great either.
The best rust prevention spray is lanolin ( from sheep wool production ) many different brands exist. Unlike wax oil for example it doesn’t dry up and flake away from metal surfaces.
My 1960 lincoln premiere hasn’t rusted in the 10 years I’ve been using it ( redo every few years ) and being a natural product doesn’t have the problems associated with petrol chemicals.
Yep, wool wax or fluid film (both products made by the same company) work great. Spray or brush right over rust, these products creep into every crack and crevice and keep rust at bay.
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