1998 Chevrolet Express Van Owner's Manual - Page 254

As shown in thechart, SAE 5W-30 is best for your vehicle. However, youcan use SAE 1OW-30 if it's going to be 0"F (- 18" C) or above. These numbers on an oil container show its viscosity, or thickness. Do not use other viscosity oils, such as SAE 20W-50. Engine Oil Additives Don't add anything to your oil. Your dealer is ready to advise if you think something should be added. When to Change Engine Oil If any one of these is true for you, use the short tripkity maintenance schedule: Most trips are less than 5 to 10 miles (8 to 16 km). This is particularly important when outside temperatures are below freezing. Most trips include extensive idling (such as frequent driving in stop-and-go traffic). Most trips are through dusty areas. You frequently tow a trailer or use a carrier on top of your vehicle. The vehicle is used for delivery service, police, taxi or other commercial application. Driving under these conditions causes engine oil to break down sooner.If any one of these is true for your vehicle, then you need to change your oil and filter every 3,000 miles (5 000 km) or 3 months -- whichever occurs first. NOTICE: Use only engine oil with the American Petroleum Institute Certified For Gasoline Engines "Starburst" symbol. Failure to use the recommended oil can result in engine damage not covered by your warranty. GM Goodwrench@oil meets all the requirements for your vehicle. If you are in an area where the temperature falls below -20°F (-29 "C), consider using either an SAE 5W-30 synthetic oil or an SAE OW-30 oil. Both will provide easier cold starting and better protection for your engine atextremely low temperatures.