I read this post on another forum (Car Talk BB). The thread was about how often oil should be changed:
quote:Please retract everything I've ever said about the possible inaccuracies / uncertainties of lab analysis...anything has to be better than this guy's "how does it feel" test. Can you imagine going to a mechanic "Hey, can you feel my oil?" You'd either get punched out or arrested.
oil change schedules and maintainence schedules are mostly bogus. They are scheduled according to averages. The only true application I have seen of most scheduled service intervals is being used by the warranty company to deny service for lack of scheduled maintinence. Oil change intervals are dependant on the amount of internal engine friction, amount of contamination from blowby gases, operating temerature, Type of lubricant used, and engine temp. I have never followed the schedule with regular oil. I have had several vehicles run fine in excess of 300,000 miles by looking at and feeling my oil on a weekly basis. Standard oil shows it's need to be changed through appearing dark and burnt and feeling thin and somewhat gritty. Synthetics are supposed to last longer and I imagine they do not show signs of breakdown as redily as regular oil does. Still if the synthetic feels gritty and or appears opaque black it means it has alot of carbon in it and should be changed. If the saturn manual says 7,500 miles and also says use synthetic only. Then you should use the synthetic reccomended. If the dealer you took it to filled it with 5w30 quakerstate than you will be needing it changed sooner more like 3,000. If the car is used and engine wear is unknown you'd be well advised to have an experienced mechanic look at your oil a few times to get an idea of what is a good interval for your vehicle. Engine wear, driving style, operating condidtions, and the type of oil used all contribute to the life of the lubricant.