this sounds like what happened last year with our 2006 Sundeck 240. The problem was traced to the impeller which had to be replaced. Its failure and the resulting overheating of the engine caused quite a bit of damage which, of course, had to be repaired too. I was told by the serviceman (not a SeaRay dealer) that Mercury recommends replacing the impeller every 3 years, or more often with heavy use. NOBODY at the SeaRay dealer where I've had service done on this since it was new had ever said anything about this. I had even had the boat in for service and numerous little repairs at the end of the last boating season and told them that the system failure and alarm had gone off on my way to the dealer; still no mention of the impeller! So my suggestion would be to have this checked and replaced if necessary.