Ok, I have a 1990 F-150 4x4 which has 110,000 miles. Within the last 5,000 miles, it has been having a terrible oil problem. Mainly at startup, it sends a huge puff of blue smoke out. When idling for a while, it starts burning oil. It goes through a quart about every 600 miles. The oil does seem to get dirty relatively quick after I change it. What could the problem be, dirty engine or worn parts? Should I try auto-rx? Thanks!