Oils recommended for your vehicle can be identified by looking for the starburst symbol. This symbol indicates the oil has been certified by the American Petroleum Institute (API). Do not use any oil wich does not carry this starburst symbol. If you change your own oil, be sure you use oil that has the starburst symbol on the front of the container. If you have your oil changed for you, be sure the oil put into your engine is API certified for gasoline engines. You should also use the proper viscosity oil for your vehicle, as shown in the following chart. (Charts says 5w30 (preferred over all) for 100F and down 10w30 for 0F and up Do not use SAE 20w50 or any other grade oil that is not recommended) AS in the chart shown previously, SAE 5w30 is best for your vehicle. However, you can use SAE 10w30 if it's going to be 0F or above. These numbers on an oil container show it's viscosity, or thickness. Do not use other visocity oils, such as SAE 20w50.
NOTICE: Use only engine oil with the API 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 you vehicle. If you are in an area where the temperature falls below -20F, consider using either an SAE 5w30 synthetic oil, or an SAE 0w30 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 recommened oils with the starburst symbol are all you will need for good performance and engine protection.
When to change your engine oil: Your vehicle has a computer that lets you know wheno to change your engine oil. This is not based on mileage, but on engine revolutions and engine operating temperature. When the computer has calculated that the oil needs changing, the GM Oil Life system will indicate that a change is necessary. The mileage between oil and filter changes will vary depening on how you drive your vehicle -- usually between 3000 and 10,000 miles since your last oil and filter change. Under severe conditions, the system may come on before 3000 miles. Never drive you vehicle more than 10,000 miles or 12 months 9which ever occurs first) without an oil change. The system won't detect dust in the oil So, if you drive in a dusty area, be sure to change your oil and filter every 3000 miles or sooner. Remember to reset the Change Engine Oil whenever the oil is changed.
This is from pages 6-16 and 6-17 of the manul for a 2001 Gmc Yukon. Mine is the Xl (= a suburban) with a 4.8 and all the options except sun roof and cassette. I have received several notices in the mail for our other GMs from the corporation about using syn oil in the winter. They say it is a good idea, so does the manual. I already do in every thing. One guy I know says his 01 or 02 GMC truck with 4.8 owners manual warns not to use syn oil. I think he probably mis-read the part about "DO" use syn oil. Plus they have been sending out those notices promoting it. He is one of those Quaker state 4x4 brand ever 3000 nothing else works guys. But I will ask to see where it says no syn next time I see him. Back to the warranty issue Pablo does this mean (unless there is some other hidden warranty contract that oil type and change interval is up to me unless they can prove that is what wrecked the vehicle or parts? If so what good are any of the oil certs except for more knowledgeable people to judge oil by? I also own 2 Harleys and they are the master of implying warranty obligation.