Went to the lake today. The boat has been in storage for 3 years. It has 16.5 hours on the engine. We left the dock and it would not build up past 3000 rpm. I stopped when I heard a beep and turned the engine off. There was a small amount of smoke in the engine compartment. I guessed it was some oil or something, I restarted the engine and the boat went to full power. I ran it for 2 to 3 minutes and the beeping returned. I stopped the boat and lifted the engine access area with the engine running. I noticed that the boat had not been de-winterized as I saw water pouring into the engine area. The temp did not get above 180 degrees indicated. I installed the three hoses and installed the four block plugs. The insulation on the piping after the exhaust risers was bubbling. I noticed that the overheat sensors had melted out of the exhaust risers. I restarted the engine and it cooled to 175 degrees. I ran the engine for another 2 hours and it rose to 180 degrees when going slow and dropped to 175 at speeds over 20 mph. I know the water pump impeller is toast and has to be replaced. My question is about the Exhaust overheat sensors at the rear of the exhaust sensors. How do I replace them? they are melted and no longer in the riser. What else do I need to look for? The engine would run to 5000 rpm and the boat attained a top speed of 50 mph with 4 adults, which is normal at full trim.