Hi all

Over the last 2 months my engine a Kubota 23 has stopped pumping raw water 3 times. First time, I think the intake got blocked and impeller went (very frustrating as just had it changed). Second time motored out, sailed for a few hours, then when started engine to come in through the bar i wasn't pumping again. The mechanic checked. Impeller and pump OK. Cleaned out heat exchanger and pumped well again. Next few weeks motored, in the river several times and pumping was fine every time with no overheating. Next time we went sailing again the motor was fine from marina through the bar. We sailed for several hours then when we started the engine again the raw water didn't pump. Have now removed the heat exchanger to have it cleaned out properly, tested and potentially replaced.

However does anyone know whether there could be other causes I need to rule out. Why would this only occur while sailing at sea - not in a river.