The oil life monitor on your car is simply an algorithm created by the manufacturer to estimate when your oil is likely to need changing based on the engine operating conditions, such as number of hours, rpm, and cold starts. The manufacturer will always put some sort of factor of safety in this calculation (perhaps 20% or so) to pretty much guarantee if you change the oil by the time it tells you there's 0% life left that you won't do any damage to your engine. The oil doesn't magically fall apart when the number hits 0%, like Cinderella's coach turning into a pumpkin or anything like that. What this means is that you should get the oil changed as soon as is practical - within 2 or 3 weeks or before any really long trips. The real reason to change your oil - you shouldn't have any metal shavings or chips in it or anything like that because that's what your filter is for - but is because your additive pack is nearly depleted. If you do a used oil analysis this will show up as your TBN - Total Base Number. Your oil has additives in it to neutralize the effects of the acids resulting from the combustion of gasoline.
