How often should you change your cars oil?

The recommended oil change interval for the Ford Model T was every 300 miles. Of course back then engines had no oil filters, oil was single grade and lacked the detergents of modern oil, and the same oil lubricated the engine and transmission.

Over the years engines and oils have improved greatly leading to longer intervals. The 3,000 mile interval has been pushed by garages at least since the 1970’s. Even in the 70’s a lot of people thought that was more often than needed. Back then my dad never changed his oil and his vehicles seemed to do just fine.

I was a firm believer in the 3,000 mile oil change interval for a long time. One of my cars made it to 172k miles before it was totaled by a hit-and-run driver. I was sure my frequent oil changes were the reason for its longevity. That car was also on its original clutch which I was convinced was due to my mastery of shifting far beyond mere mortals.

Manufacturers now recommend much longer oil change intervals. Some owner’s manuals specify 12,000 mile oil changes.

Oil can need changing due to becoming acidic, being contaminated, because the additive packages break down, or viscosity increase. How long it takes for these problems occur depends on many things like how hot it is, the length of trips you take (people who only drive short distances cause more problems), how hard you drive, etc. The values manufacturers recommend are what they consider safe for their engines.

Both of my cars are Mazdas and the recommended intervals for them are 6,500 and 7,500 miles. I drive about 10,000 miles year and I change my oil every 5,000 miles since that is a easy number to remember. When my odomitor ends on a 5 or 0 I take it in for a change. Since Mazdas are prone to lifter noise I use synthetic 0w30.