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warburton
warburton

Posted: Mon Aug 02, 2010 9:27am

Post Subject: coolant loss

my boat has a bmc 1.5 with bowman heat exchanger. whilst cruising the bowman has started to lose a little water, but when i stop the engine the water level falls and empties the header tank. i can not see any water exiting the engine when this happens = ta bob

Tony-B
Tony-B

Posted: Mon Aug 02, 2010 12:53pm

Post Subject: coolant loss

Dear Bob, If the water level falls within minutes of stopping the engine then you definitely have a problem. If it falls over the period the engine takes to cool down then a fall in level as the coolant contracts is normal, but on a heat exchanger system (as opposed to a skin tank system) it should not amount to more than an inch or two. If you are filling the heat exchanger (which often incorporates a header tank) to the brim each time before starting then again it would be normal for the expanding water to force its way out. However if you only fill to within about one inch of the filler neck and it is still leaking I think a new pressure (filler)cap may be required. Once you rule out a faulty pressure cap look on the front of the engine immediately below the engine water pump pulley for signs of antifreeze, rust or water stained streaks. If you find any then the water pump needs renewing. A slight leak anywhere on the system may well evaporate off a hot engine so there can be no signs of a leak. My advice as the next step after a good visual check for leaks and changing the cap if required would be to hire/borrow a cooling system pressure tester and pressurise the cold engine to about 15psi. Then look for leaks which will not be evaporating. Finally we can not totally rule out a slight head gasket fault but without overheating it is not the most likeliest of diagnoses. Tony Brooks

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