The conventional wisdom is to change the oil every six months normally, and up to a year on a high quality synthetic.
I'm curious: why the change interval at six months?
The reason I ask is that my elderly mother only drives her 1999 Olds Cutlass, (with 52K on it), less than 100 miles a week, the past few years.
The dealership had her convinced to change the oil every 3 months, so she was changing the oil with less than 1200 miles on it.
I told her to change it at 3000 miles. Depending on how much she drives, she could easily exceed 6 months.
I figured that while her car is sitting in her garage, (which it does, several days every week) the oil isn't breaking down...or is it?
I do have her 'trained' to take her car out on the freeway, and drive it for about 5 to 7 miles, rather than just driving the 1 mile to church, or the library, etc., and back. So, she's not doing too much 'short trip' driving. She really doesn't understand why, but she does it.
I check her oil, and it is still quite 'clean' looking, on the dipstick, and on a white paper towel, at around 3000 miles.
I do not know what brand of oil the dealership is using; I'm sure it's dino oil.
So what's the 'conventional' wisdom for dino oil: change at less than 3000 miles, if the time exceeds 6 months?