The biggest enemy of your Challenger’s body is salt (sodium chloride). It can severely detract the appearance of your car and result in costly body work. Unfortunately, if you live in the northern part of the U.S., and your car is a daily driver in the winter, road salt is unavoidable. Parts most at risk from salt damage include the exhaust system, muffler, coil springs, subframe and hydraulic brake system.
When saltwater and metal react, a process called electro-chemical corrosion occurs. The ions found in metal dissolve in water. Saltwater also contains ions and is an excellent conductor of electricity. When this happens, the ions in saltwater attract the ions from other compounds which in turn are attracted to the metal’s ions. That is when corrosion occurs.
Water doesn’t have many ions and that’s why it conducts electricity poorly. Salt contains ions and when it’s dissolved in water, the saltwater becomes a better conductor. It is made up of sodium ions (who are positively charged) and chloride ions (who are negatively charged). That is why the flow of the electrical charge is carried by ions, and not just electrons moving. Chemical reactions occur immediately once the metal is exposed to the environment and it’s a continuing process as long as it remains exposed. However, the rate of rust formation on your car is highly dependent on the type of environment it encounters regularly and the preventive measures you put into place.
If you have to drive your Challenger under winter conditions, the best preventative measures are to keep your car waxed and to take it to a car wash (one that does not use recycled water), frequently, and thoroughly clean the exterior and chassis areas. Also, do not park a salt-covered car in a heated garage. This will just accelerate the corrosion process.
Automakers use a salt spray (or salt fog) test to check corrosion resistance of materials and surface coatings. Salt spray testing produces a corrosive attack to coated samples in order to evaluate the suitability of the coating for use as a protective finish. The appearance of corrosion products (rust or other oxides) is evaluated after a pre-determined period of time. Test duration depends on the corrosion resistance of the coating. Generally, the more corrosion resistant the coating is, the longer the period of testing before the appearance of corrosion/rust. The salt spray test is one of the most widespread and long-established corrosion tests. This type of test is popular because it is relatively inexpensive, quick, well standardized, and reasonably repeatable. Although there may be a weak correlation between the duration in salt spray test and the expected life of a coating in certain coatings such as hot-dip galvanized steel, this test has gained worldwide popularity due to low cost and quick results.
Most salt spray chambers today are being used not to predict the corrosion resistance of a coating, but to maintain coating processes, such as pre-treatment and painting, electroplating, galvanizing, etc., on a comparative basis. For example, pre-treated + painted components must pass 96 hours of a neutral salt spray, to be accepted for production. Failure to meet this requirement implies instability in the chemical process of the pre-treatment, or the paint quality, which must be addressed immediately so that the upcoming batches are of the desired quality. Most commonly, the time taken for oxides to appear on the samples under test is compared to expectations, to determine whether the test is passed or failed.
In the factory, car bodies are protected with special chemical formulations, typically phosphate conversion coatings. Some automakers galvanize part or all of their car bodies before the primer coat of paint is applied. If a car is body-on-frame, then the frame (chassis) must also be rustproofed. Paint/clearcoat is the final part of the rustproofing barrier between the body shell and the atmosphere.
In the Brampton factory paint shop, the Challenger is dipped in a series of submersible baths, as part of the corrosion prevention process. In one of the baths, the bare metal shell is dipped in a zinc phosphate solution. This changes the chemistry of the metal surface by bonding zinc molecules to the steel. This process prevents any scratches or stone chips in the paint from becoming creeping rust.
After this initial bath, the car undergoes four stages of paint: E-coat (bath that alters the electrical charge of the metal to bond the paint to the pores), primer, color and clearcoat. Look at the 16:26 minute mark of the following Ultimate Factories video:
Despite these protections, some daily driver Challengers have experienced rusted lower body panels. The identified culprit is the foam that is injected in the rocker panel area, from the front wheel well back to the rear wheel well. It tends to wick water and causes metal corrosion. Unfortunately, no amount of rustproofing can counteract this problem.
Dodge is aware of this problem and the 2015 models have a better bulkhead in the front portion of the rear wheel well, as well as more tightly fitting plastic wheel well liners in back. These changes will, hopefully, resolve this long-standing issue.