The other day heading out in the fog i briefly hit bottom doing only 5 kts, backed out without getting stuck. Later on after about 3000 RPMs the engine started overheating so i had to back down to 1000 RPMs all the way home for about 8 miles. Any faster the temp started to climb. At one point the temp alarm went off, lost some of my coolant. Checked for a split hose or something, found none. Added a gallon of water and kept speed down to 1000 RPMs and was ok for the ride home. At the dock just idling, for 5 mins temp was 200deg. once i put the fresh water hose on to flush, the temp went down? Could i have mud in the raw water cooling system? Any one with experience with something like this please reply or anyone who knows what this could be. I primarily do all maintenance on my engine and I can't figure this one out.