Preventative Maintenance Tip for Cooling System

It has been said that internal engine corrosion only happens in salt water boats or boats winterized without antifreeze (i.e. dry).  To the best of my knowledge, my boat has always been freshwater; but as the fourth (at least) owner, I can't verify the steps taken for winterization in the past.

First the disclaimer: while I do like the Bukh engine overall, especially for it's reliability in starting and ease of operation, I think it has one serious, potentially fatal, flaw, and that is the narrow passages at key points in the cooling system.  I feel this is a major issue not only because of the ease in which these passages can become plugged, but because of the potentially disastrous consequences without any outward signs of trouble.  Not a robust design IMHO.

One such point is the elbow at the fitting where the cooling water from the engine merges into the exhaust elbow.  The fitting, as previously discussed by Frank in another post, is only 1/4" ID and could easily be plugged by any debris or flakes of engine corrosion.  The solution is to install an inline water filter in the hose between the thermostat and the inlet port to the exhaust manifold on the port side.  A filter like the Jabsco 36400-0000 does the job nicely:  http://www.defender.com/product3.jsp?path=-1|51|2234255|2234258&id=121067

The other benefit is that the clear casing is another place where you can check to ensure water flow.  Be sure that the hose clamps are not too tight (crushing the barb and blocking water flow) and not too loose (allowing air in which would reduce water flow) and that the filter is oriented the right way for water flow!  I have had this filter in my engine for 4 years now and it has been very helpful in trapping debris.

The other weak spot in the system, described above, is the one I just dealt with.  On our first motor out of the boatyard this year after 20 minutes of running at 1700 rpm in smooth water, the engine overheat alarm went off.  There was no other indication of  any problem as cooling water was coming out of the boat exhaust normally.  

After checking the hoses and thermostat, I traced the problem to the water inlet port below the air intake on the starboard side.  To remove this inlet port housing you'll need to remove the starboard bulkhead (unless you are a contortionist).   

There are two bolts underneath you'll need to loosen with a 10mm box wrench to remove the inlet housing.  When you remove the housing, water (and maybe sediment) will gush out so have paper towel handy.  The pictures below show what came out of my engine.  I was astonished at the amount of flaked metal sediment!  The picture with the paper towel is showing only 15% or so of the total amount that came out.  The inlet pipe was so densely clogged that I had to chip the sediment out.