Oil

My father changes his oil religiously on his car at 3000 miles.  Most mechanics say you can easily go 5000--even more with the synthetic oils like I use for my car.  I've long ago given up trying to get him to go further between oil changes.  It's pointless. He won't budge.  I can't talk him into trying synthetic oils, either. I think they hold up better. nope, it's plain old cheap oil.  

Of course, some people never change their oil at all.  They just add new oil once in a blue moon when the dipstick comes up empty.