Two points really, the first is that I've added some sound insulation to the top of the engine compartment on my B36, and the reduction in engine noise in the cockpit area was astonishing. As a result, when my boat engine overheat alarm went off last week for the first time since I bought it five years ago, it was very easy to hear.
The second point of course was why did the engine get hot enough for the alarm to sound ? After limping back to my mooring, I started to examine and take apart the various parts of the cooling system, and to cut a long story short, I took off the rubber end caps from the md2020 heat exchanger. This was the first time ever that these caps had been removed as the paint on them remained original and untouched. Once the forward cap was off, three pieces of impeller vanes were found along with a piece of shell barnacle about 10mm in length and breadth plus some smaller parts of presumably the same barnacle shell. In all there was sufficient debris to cover about 70% of the ends of the tubes within the tube nest. Hopefully I've found the problem that caused the overheat, but it's worth while mentioning that every single impeller that I've changed, and that is one each year, in all instances the impellers were in very good order with no missing parts. That means that these impeller vanes were lost during the period of the boat's previous ownership. The moral of course is that I should have checked it out sooner. Prior to the overheat there had been some warning signs which was that the flow of water did not seem to be as much as I'd have anticipated. And there was some vapour evident which I was undecided (at the time), whether it was smoke or steam.
So the moral is to take the end cap off and check there is nothing loose that might block the tubes for the heat exchanger, particularly if like me, the boat was bought secondhand. I'll let you know if the overheat problem has been solved after I've put everything back together next week.
