I thought I might have had a problem with the fresh water side of the cooling 
system of my Universal M4-30 engine because it was heating water very slowly. I 
now think that it is just that the sea water is cold this time of year and it 
was taking longer than I expected. All was fine with lots of hot water after an 
extended motoring session at speed as opposed to idling at the mooring. 
However, it made me think about this side of the cooling system.  Presumably, 
minimal fresh water circulates through the heat exchanger until the thermostat 
opens.  My question is, what drives that water circulation.  I know to check 
the impeller on the raw water pump side periodically, but I have seen no 
mention of doing the same for a water pump on the fresh water side.  That pump 
appears to be pretty inaccessible on my engine anyway and nothing in the 
routine maintenance section talks about periodic replacement of an impeller 
there.  So I am guessing it does not have an impeller that needs replacement, 
but I can’t find anything relevant in the manual.  Thanks- Dave

David Knecht
S/V Aries
1990 C&C 34+
New London, CT



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