1998 Chevrolet Express Van Owner's Manual - Page 297

Underbody Maintenance Chemicals used for ice and snow removal and dust control can collect on the underbody.If these are not removed, accelerated corrosion (rust) can occur on the underbody parts such as fuel lines, frame, floor pan and exhaust system even though they have corrosion protection. At least every spring,flush these materials from the underbody with plain water. Clean any areas where mud and other debris can collect. Dirt packed in closed areas of the frame should be loosened before being flushed. Your dealer or an underbody car washing system can do this for you. Chemical Paint Spotting Some weather and atmosphericconditions can create a chemical fallout. Airborne pollutants canfall upon and attack painted surfaces on your vehicle. This damage can take two forms: blotchy, ringlet-shaped discolorations, and small irregular dark spots etched into the paint surface. Although no defect in the paint job causes this, GM will repair, at no charge to owner, the surfaces of the new vehicles damagedby this fallout condition within 12 months or 12,000 miles (20 000 km) of purchase, whichever occursfirst. This applies only to materials manufactured and sold by General Motors. Bodies, body conversions equipment or not made or sold by General Motors are not covered.