Last night while fishing I noticed that my fans were on long after I turned the truck off. Today, hot air out of a/c and check engine light came on. I went straight to parts house and the computer threw P0128. My Temp gauge is at lowest possible point and does not go up no matter how long I let it run. Coolant was down about 1/2 an inch from the full line. Oil level is fine. No obvious leaks