A 2005 Chevy Colorado 3.5L requires 5W-30 oil for optimal engine performance, as this is the factory recommended grade of motor oil. The oil should be changed at regular intervals to ensure that your vehicle continues running smoothly and efficiently, as dirty or old oil can lead to excessive wear on the internal components of an engine over time. When selecting a type of motor oil for you 2005 Chevy Colorado 3.5L make sure it meets the American Petroleum Institute (API) “Starburst” requirements and that it has been certified by either API SN or ILSAC GF-4 standards; these are both required in order to meet warranty requirements set forth by General Motors Corporation (GM). Additionally, when purchasing an oil filter make sure it is specifically designed for use with synthetic oils and has been approved by GM as well. Following these guidelines will help keep your car running in peak condition no matter how many miles you put on it!