2003 Buick Century Owner's Manual - Page 233

As in the chart shown previously, SAE 5W-30 is the only viscosity grade recommended for your vehicle. You should look for and use only oils which have the API Starburst symbol and which are also identified as SAE 5W-30. If you cannot find such SAE 5W-30 oils, you can use an SAE IOW-30 oil which has the API Starburst symbol, if it's going to be 0°F (-18°C) or above. Do not use other viscosity grade oils, such as SAE IOW-40 or SAE 20W-50 under any conditions. When to Change Engine Oil (GM Oil Life System) Your vehicle has a computer system that lets you know when to change the engine oil and filter. This is based on engine revolutions and engine temperature, and not on mileage. Based on driving conditions, the mileage at which an oil change will be indicated can vary considerably. For the oil life system to work properly, you must reset the system every time the oil is changed. When the system has calculated that oil life has been diminished, it will indicate that an oil change is necessary. A CHANGE OIL SOON light will come on. Change your oil as soon as possible within the next two times you stop for fuel. It is possible that, if you are driving under the best conditions, the oil life system may not indicate that an oil change is necessary for over a year. However, your engine oil and filter must be changed at least once a year and at this time the system must be reset. It is also important to check your oil regularly and keep it at the proper level. If the system is ever reset accidentally, you must change your oil at 3,000 miles (5 000 km) since your last oil change. Remember to reset the oil life system whenever the oil is changed. 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@ meets all the requirements for oil your vehicle. If you are in an area of extreme cold, where the temperature falls below -20°F (-29"C), it is recommended that you use 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 at extremely low temperatures. Engine Oil Additives Don't add anything to your oil. The recommended oils with the starburst symbol are all you will need for good performance and engine protection. 5-16