On a fairly new car, Covering the underbody with a sealing compound will discourage corrosion. It can be sprayed on under pressure or brushed on. Where to apply underbody sealant But if there is already considerable rust, Applying a sealant will accelerate corrosion rather than protect the underbody against it, Because the corrosion will spread unseen and unchecked beneath the covering layer. Raise the car securely on ramps or axle stands, and check the underside. If the floor and the insides of the front and rear wings are already rusty, Do not attempt to seal. A sealant will be effective only if the underside of the car is completely clean. Wash it thoroughly with hot water containing a small amount … Continue reading Applying underbody sealant