How does the car calculate when an oil change is needed? Just curious. I still change mine every 3-5k miles. I know BMW uses a mixture of how the car is driven and gas mileage to determine when the car is due for an oil change. I have about 3k on mine since last oil change and the car says 38% oil ife left.

Good question. I would like to know this as well.

I dont recall all the factors, but some are these (since last oil change):

Number of cold starts, cold starts are the harshest on oil.
Average oil temperature
Average RPM

I am not sure, but I also heard it will flag high RPMs, as in how often you exceed 5k.

distance ,temps.

short runs really trigger the warning,

when i wasnt running my car much because it was having work done,i would start it up every week to keep it running good,but it never got upto full temp,the % left went from 80 something% to 30 something in like 5 weeks,and i only put a handful of miles on it moving it around the property.

i

I changed mine today, it was at 34% and had (barely) 2000 miles since the last change. I use my 96 as an 'extra' car in that I don't drive it that much, and it does sit for extended periods of time. I have noticed that it 'uses' up a percentage when it sits. I only use either royal purple or lucus full-synthetic, so I really don't have to change it that often, but I'd rather spend $45 than whatever money and agg it takes to replace the engine-118,000, and it runs smooth and uses no oil between changes. Cheap insurance.

time certainly has a function. my ride was in the paint shop for a month and when i got it back it was tellin me its time of course it was synthetic so i reset it and now i will go to 50% than change

my method is this:

since the oil alert was made for regular oil and i am using synthetic only,i leave the oil alone until it visibly starts to get dark,upto 2 full resets of my oil alert,since i work close to home i never go more than 6000 on my oil,but if it looks nasty at 3000 i change it