oil changes

I thought I would add my 2 cents. I will agree that the oil today is way better then it use to be in the 60s and 70s. Back then when a engine had around 75.000 miles on it . You would see it smoking going down the road. Back then you had to change your oil every 2,000 miles if you wanted your engine to last. I am still a fanatic on changing my oil. If I use mineral oil, I change it every 3000 miles. If I use synthetic oil I change it every 5000 miles. I know I could go longer on the synthetic oil. In fact in my diesel I use amsoil heavy duty synthetic diesel and marine oil with the amsoil filter. According to amsoil using this oil and their filer I can go 20.000 miles or 1 year between oil change. As often as I change the oil I could use their cheaper synthetic oil and be just as well off. But this is what I go by besides humans are creatures of habit. Back in the 60s when my dad was changing oil every 2000 miles. He said son, a oil change is the cheapest motor overhaul your ever going to get.I said to myself, he is right.Like I said ,I do go overboard on the oil change intervals . But like my dad said it is the cheapest motor overhaul you are ever going to get. Plus when you do have to work on my engines. When you pull the valve covers or the intake. The block looks like brand new with fresh motor oil poured down it. Their is not sludge.