how often dose synthetic oil need to be change. live in torrance ca. i was told by my service station every 3,000 miles.
The answer is in your owner’s manual. Since you did not indicate what year car you have we could only guess. The proper time to change is usually indicated as XXX miles or XXX months whichever comes first. It is also dependent on the driving conditions (short trips etc will call for more frequent changes.) Your service station or the dealer are not ideal sources of this information. Most service stations and many dealers will always say 3,000 miles, but then them make money changing oil, which I would guess you already figured out and that is why you wisely asked the question.
For most cars and drivers it would be closer to every 6,000 miles or 6 months whichever comes first. Cars and oils have changed a lot since the 50's and 60's when 3,000 miles was the norm.
If you want to change your oil every 3000 miles, do not use synthetic oil. You could easily go 6000; Mobil-1 guarantees 15,000 miles if your oil filter will last that long. But Saturn will not underwrite your engine unless you meet their oil change rules. I’d switch to classically refined oil and leave synthetics to fleet owners.