My 1995 Chevy diesel has 231,000 miles on it and it has been very well kept. It was sitting outside running and ideling for an hour, looked like it was lightly smoking..I jumped in it and started driving it down the road and then noticed it was smoking really bad. I pulled over and checked it. Antifreeze was low, everything else was fine. My low antifreeze light came on and it continued to keep smoking badly. This is where I'm at.??? Any suggestion on what you think might be happening?