2003 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 395

What Kind of Engine Oil to Use Oils recommended for your vehicle can be identified by looking for the starburst symbol. This symbol indicates that the oil has been certified by the American Petroleum Institute (API). Do not use any oil which does not carry this starburst symbol. If you choose to perform the engine oil change service yourself, be sure the oil you use has the starburst symbol on the front of the oil container. If you have your oil changed for you, be sure the oil put into your engine is American Petroleum Institute certified for gasoline engines. You should also use the proper viscosity oil for your vehicle, as shown in the viscosity chart. RECOMMENDED SAE VISCOSITI GRADEENGINE OILS HOT WEATHER LOOK FOR MIS SYMBOL n 7 SAE 5w-30 RECOMMENDED II L Ar ACCEPTABLE IF5W-3OIS NOT AVAILABLE COLD WEATHER DO NOT USE SAE1OW-40,SAE 20W-50 OR ANY OTHER VISCOSITY GRADE OIL NOT RECOMMENDED 5-20