Coolants age differently, depending on the stress, and regular replacement is therefore necessary for safety purposes. Anti-freeze protection is primarily corrosion protection, so that coolant is used worldwide and is an all-year-round subject from the point of view of maintenance. When replacing metal components in the cooling circuit, the new components have many reactive surfaces. In order to provide these with a sufficient quantity of organic or inorganic corrosion protection inhibitors, regular replacement of the coolant is also advisable for this reason.