I too had a Vetus Water Lift Muffler melt.  Seems like many have had this happen as reported on this forum.  In my case it melted but not before the exhaust hose from the turbo outlet to the muffler caught on fire (internally).  Only when a hole melted thru the muffler, allowing black smoke to pour out into the engine room did I know something was wrong.  I smelled this problem.  I visually checked the temp gauge on the Yanmar engine panel (which appeared normal), noted that no alarms sounded, opened the engine hatch and a column of black smoke poured out.  I couldn't see any flames but I thought the engine room was engulfed in fire the smoke was so thick.  I immediately shut down the engine but the only way I could enter the engine room was with a respirator.  I thought the boat was about to burn to the water line.  This occurred in a narrow channel with limited maneuvering and or sailing options and less than 50 hours on the sea water impeller.    30 seconds after shutting off the engine the high temp alarm on the Yanmar panel sounded.  Way, way, way, too late. Following repairs I installed the Borel Mfg exhaust temp system on both the main and genset exhausts.   

This is Borel's web site:  

http://www.borelmfg.com/index.html

Borel used to offer, and may still be willing to build for you, a bilge pump RUN-ON alarm.  I have had their Run-On alarm for many years but don't see it currently offered.  This alarm will sound if the bilge pump runs for more than a programmed number of minutes.  I wouldn't sail without this one.  I was making water one day and the seal on the Dessalator low pressure feed pump failed flooding the engine room with sea water.  The bilge water level alarm sounded, eventually, but by then there was 2 inches of sea water sloshing back and forth in the bottom of the engine room.  The bilge pump had been trying to keep up with the leak for heaven only knows how long.  Could have burned up the bilge pump etc.  My Borel run on alarm is set to sound if the bilge pump runs continuously for more than 2 minutes.  I test it every few days.   Again, I consider it an essential piece of safety equipment.  I also have their bilge water level float alarm and it is velcroed to the Amel bilge pump float gray column pipe about 4 inches lower than the Amel mounted bilge water sensor.

Just my thoughts. 

Gary Silver

s/v Liahona   Amel SM #335

On the hard at Jolly Harbor, Antigua