I usually go about yearly, but I use synthetic, and drive about 5-6k a year.

Years ago I had a friend (son of a single mother) who decided he needed to change his oil, so he asked me to show him how. I told him to bring the car over to the shop and we'd get it done. Started draining the oil, and I got a punch and punched a hole in the filter to let it drain. He looks at me and asks if he really had to change the filter. I asked how long it had been, and he had the car for about 20k miles then, and hadn't ever changed it. He never had the oil changed either, he would just add new to top it off since it leaked out. For some reason however, that car (85 mustang) kept going for about 5 more years and ended up with almost 200k on it.

 

i wouldnt doubt it those 5.0l have a lot of heart i use to own a 89 f150 4x4 and it had close to 300k miles on the factory motor/trans, never rebuilt
but that was back when they built trucks to last you forever

 

I run Valvoline 10W30 Conventional and a Mopar or a Purolater Oil Filter, and change it every 2000 miles which is usually about every month to month in a half, I have 186,000 miles on her. I had my Valve Covers off 2 months ago and the valve train was like new!!!