Robotech said:
I need to find the tests that were done on this but there was a test someone did with changing your filter at 5K mile intervals and only changing the oil when it needed it. The folks doing the test went about 25K miles before the oil was loosing it's lubricating properties. More importantly, they found that changing every 3K miles may actually be detrimental to protecting the engine. I can't remember the details (again, need to find the post) but I've gone by the engine oil life monitor in my Grand Prix for quite a while and it is pretty dead on when it comes to when to change the oil as far as the oil's condition is concerned.
Also, for those of you who like to use Mobil 1...check out Wal Mart. They sell 5 quart jugs of Mobil 1 for $20. Not bad for Mobil 1.
I remember that one, robotech. I personally used synthetic in my Quad 4 - changed the filter every 5K and the oil every 10K miles. The car now has ~ 160,000 miles and counting on it... <shrug>
I talked with a powertrain engineer and they said that the oil life indicator is quite accurate and reasonably conservative (meaning the oil is still very good condition after you reach 0% life). I've known people to go >9,000 miles (mostly low load highway driving) until their life indicator gets to "change oil soon." Many of these cars are still driving around with >80,000 miles and no problems...
...the margin gets a bit higher if you use synthetic. And it IS driving style dependent. Another acquaintance that beats on their leased car only gets on average about 2600 miles before their indicator gets to "change oil soon".
bottom line - you're fine if you wait until it tells you, and you aren't doing any harm if you change it religiously every 3000 miles - but you may have a lot more life in that oil that you aren't getting the benefit from.
I personally now change all my cars at 5000 miles (don't have any that have an oil life indicator). When I get my turbo kappa - I'll follow the oil life indicator and change it only when it says.
JM$0.02.