2003 Chevrolet Impala Owner's Manual - Page 271

What Kind of Engine Oil to Use RECOMMENDED SAE VISCOSITY GRADE ENGINE OILS 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. Ifyouchoose 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. 5-18 Oils recommended for your vehicle can be identified by looking for the starburst symbol. HOT WEATHER ' I - SAE 1OW-30 ACCEPTABLE IF 5W-30 IS NOT AVAILABLE SA€ 5W-30 . . RECOMMENDED I You should also use the proper viscosity oil for your vehicle, as shown in the viscosity chart. COLD WEATHER DO NOT USESAE 1OW-40, SAE 2OW-50 OR ANY OTHER VISCOSITY GRADE OIL NOT RECOMMENDED 3400 (Code E) V6 Engine