Join Date: Aug 2006
Location: Arlington, VA
Thanked 11 Times in 9 Posts
Rep Power: 11
"It was sudden, from one day to the next."
Clogged water input or loss of coolant. Check obstructions in raw water inlet...strainer, seacock, etc. Then, check impeller. If you haven't changed it this season, do so. If there are missing rubber parts, they may be downstream somewhere, and clogging the heat exchanger, water jackets, etc. Check coolant level and be sure to use 50% antifreeze/50% water solution.
Lots of other possibilities, as mentioned, but a clogged or damaged coolant system seems most likely for a SUDDEN change in cooling performance.