White smoke from exhaust and clanking sound?

I have a 97 Plymouth, and so far its been a VERY dependable car. For awhile I neglected it and it ran on very low oil for some months. It still runs strong, but when it idles it gets moody. And after idling when I go white smoke comes out of the exhaust. Not a whole lot, but sometimes I can see it when I look back. And also theres occasionally a clanking sound, usually around a certain RPM just before the car accelerates from, say, idling around a corner. You know when a car is overheating really bad and it has clanking noise? Its like that but a little less prevalent. But like I said, when the car is going, its as strong as it was when I got it 5 years ago. Recently there was an overheating problem but I had the thermostat replaced and its fine now. So are these major problems? I'm trying to decide if I want to sell my car for something else while I still can. What kind of money would I probably be spending when these problems develop further?