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Posted: Sun Oct 09, 2011 5:29pm

Post Subject: cooling

Hi Tony, i have a isuzu 55 fitted in my 60'x 10'widebeam which has been running fine for the 5years i have owned it[from new].This summer for no reason it has started to overheat when the revs are increased to 1200,but not all the time it might happen once in 4 or 5 days.I have fitted a new thermostat and bleed the skin tank of air.There are no leaks from any of the hoses and no water in the oil have you any ideas on what route i should take next???many thanks Richard.


Posted: Sun Oct 09, 2011 5:55pm

Post Subject: cooling

Check the alternator drive belt - the one that runs over three pulleys - especially if this coincides with higher battery charging rates because it could be a slack belt. Then double check that all the air (or gas) really is out of the skin tank. If both are OK it may be a good idea to either check the temperature gauge reading with an infrared thermometer to ensure it is a true reading. I rather suspect this could be a failing temperate sender. Unfortunately you leave me to guess the type of cooling system your boat uses. If it is NOT a skin tank system please come back with a description of the system. At this time of year falling leaves can pack around the spinning prop causing an apparent loss of power. These float away when you either go into neutral or give it a burst of reverse. They could overload the engine, especially if you rev up to maintain speed, so make sure that is not the cause. After those items I think you need an engineer to check the coolant with a special liquid that will tell them if the head gasket has failed, but at them moment check the other stuff first. I would add that you have not given me exact symptoms of this "overheat" so it could be something normal like the temperature gauge rising as the calorifier gets hot and stops pulling heat from the system. This will not be the case if you end up with system gushing from the engine filler. I have also known people who overfill with coolant describe the normal expulsion of liquid caused by heating as overheating which it is not. Tony Books

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