My husband is an auto technician and he tells me all the time that no matter what the manufacturer says, if you want to keep your car running smoothly and for a long time, then you should change your oil every 3000 miles or every 3 months, whichever comes first. His theory is that car manufacturers are in the business of selling cars so they'll tell you that you only need to change your oil every 7000 or 10000 miles. The problem is that this is too long and stuff will build up in your oil. In another 5 years your brand new car won't be running as well and you'll need to buy a new one. The car manufacturer won and you end up shelling out money for the next car loan. Instead, change it every 3000 miles and keep your car running smoothly for a good 10 to 15 years at least.
Every 3,000mi no matter what. Months really don't matter. If the oil just sits in the car and you don't drive it it's not a big deal. I mean think about it how can oil break down if it's not getting used. I change oil for a living and they will try and tell you to go more miles. They say the oils are better and no they are not and even if they were your engine will still break them down at about 2,500mi no matter what you put in it
The best way to know when to change your oil is to have it analyzed at say 3000 and 5000 or even 7000 miles to see at what milage your vehicle has broken down the oil. Only then will you know truly when to Change it . I change my oil every 5000 miles and have not had it analyzed.
See what your vehicle manufacturer says. Most cars now have sealed engines, tighter tolerances and oils themselves are vastly improved over years ago. It used to be 3000 miles would be the change mileage but I have not seen a company recommend that if at least a decade
5000 miles is the new norm, and depending on the oil ( synthetic vs. conventional) and the car or driving type, you can go to 15,000 miles.
We change the oil/filter in our classic car collection once a year and run synthetic in all the cars.