The causes of accelerated corrosion are divided into two groups and are related to:
- with design or technological features of specific models;
- with external influences.
The first group includes:
- occurrence of high stresses and vibrations of the body metal;
- the presence of "pockets" in the supporting sections of the bodies;
- use of thin metal sheet (0.7–0.8 mm);
- use of metal with impurities that increase the rate of corrosion;
- the presence of corrosion concentrates in the form of moldings and other decorations.
External influences include:
- sulfur compounds, carbon dioxide and chlorides found in the environment;
- salt solutions used to combat ice.
In our conditions, various salt solutions have the greatest impact, as they lead to the formation of conductive "bridges" between body parts, which, as a rule, have different electrical potential. This causes the fastest type of metal destruction - electrochemical corrosion. The point is that all cars have a single-wire electrical circuit, and, therefore, currents "walk" through the body from one consumer to another.
We will not go further into the theory, leaving it to specialists in the field of corrosion, and will turn to practical issues. These results are based on the use of three types of devices during the examination, allowing us to evaluate:
- change in the thickness of "live" metal, that is, not subject to corrosion;
- the degree of erosion of the metal from the inside, in other words, the degree of its loosening or destruction by oxides;
- thickness of cosmetic layers (paints, putties), which allows you to determine whether the body has been repaired and attempts to hide it.
The results of the examinations carried out by specialists allow us to draw the following conclusions:
1. In the conditions of our region, the rate of corrosion penetration into metal for cars used in winter is 0.2 mm per year and 0.1 mm per year for cars that have not seen salt.
2. Corrosion develops especially quickly in areas that have undergone body repair, and even more quickly if this repair was carried out using welding or soldering, since electrochemical pairs are created from dissimilar metals. For those buying a car, especially a foreign car, this is of fundamental importance. It is not for nothing that thrifty Europeans almost always sell even a slightly damaged car (true, having received insurance) for next to nothing - $1-2 thousand. The reader probably knows for how much they are then resold in our markets. But if you are lucky enough to discover a hidden defect before making a purchase, know that the real cost of such a car is 25-50% lower than that of an undamaged one. We must not forget that sooner or later you will sell the car, and without experts, only very naive people make expensive purchases now.
(Information copied from the website: mercedesman.ru)
3. The corrosion process is fastest in cars used in winter and stored in garages, especially warm ones, without preliminary dissolution of salts with running water. We emphasize, not washing, but dissolving. Those who believe that by washing the lower part of the car with a strong stream, they are doing a good deed are very mistaken. Salts dissolve easily even without strong pressure, but protective coatings from a powerful stream rather quickly "stick off" from the metal, sag, creating only the illusion of protection. In the cavities formed between the metal and the sagging mastic, corrosion develops much faster than on open metal.
It is highly recommended not to wash a car with hot water, since due to different temperature expansion, the protective coatings that warm up first "slide" off the metal, creating a negative effect.
Those who believe that the thicker the protective coating, the better, are wrong. It's just the opposite. The main thing is that there are no breaks in the coating, and therefore it must be renewed regularly.
In conclusion, here is some practical advice. Of the two cars, the better one is not the "younger" one, but the one in which the metal destruction process has not penetrated to a depth of more than 0.4–0.5 mm. In this case, no treatment can prevent the formation of holes in one and a half to two years. And vice versa, even an old car that has had reliable protection from the start of operation will serve for many more years. In our conditions, it is possible to repair the engine and chassis of a foreign car, but it is not economically feasible to repair a heavily rotted body.