The 4WD Heavy Duty system has been specifically designed to protect the Four Wheel Drive or SUV vehicle from rust, even when these vehicles are exposed to *FREQUENT use within highly corrosive environments such as; driving on salted roads or beaches. This system may also benefit older 4WD vehicles that are suffering from minor existing rust problems. But remember, as good as this product is, it is not a miracle cure for badly rusted vehicles, as the more rust a vehicle has, the harder it is to stop. (*Weekend use)