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spickard
spickard

Posted: Sun Feb 05, 2012 1:48pm

Post Subject: BMC Thornycroft 4 cylinder diesel

Lately I have noticed high bilge-pump usage when the engine is running, Investigation found the cooling system overflow discharging constantly. The cap looks ok but I didn't test it in hot water and intend to replace it, my question is if a new cap doesn't resolve the problem is there other test/investigation for me to do?

Tony-B
Tony-B

Posted: Sun Feb 05, 2012 7:10pm

Post Subject: BMC Thornycroft 4 cylinder diesel

Well, yes, but without any indication of running time and temperature reached they may well not be appropriate. I have no idea why you want to put the cap in hot water - it will tell you nothing but you might want to do it to a thermostat. It would help to know how much boating experience you have and on what type of boats because the way you write about the bilge pump suggests to me that your engine should have boiled dry and seized up so I am wondering if you also have a leaking weedhatch or are using some form of raw water cooling and that there is a leak on that system. It would also help to know what type of cooling system you have. The way the question is written and the lack of information makes me suspect that you are new to boating and are simply overfilling the cooling system so when the coolant heats up and expands the surplus spills out. Try this - fill the header tank to the brim, get the engine up to running temperature (coolant will spill out), let the engine cool down and when COLD note the coolant level in the header tank. This is the correct level so never fill above it. Tony Brooks

Tony-B
Tony-B

Posted: Mon Feb 06, 2012 12:13pm

Post Subject: BMC Thornycroft 4 cylinder diesel

Further to my reply above. I have been pondering this overnight and can still not equate the small volume of water lost from the cooling system and which would normally end up in the engine drip tray - not the bilge - with "high bilge pump" usage. If you have normal narrowboat tank cooling inspect the weedhatch seal and the stern gland whilst under way and also when stationary with the engine running. Inspect the ledges either side of the swim for wet areas. Then pump out and rag dry the bilge and look for spreading areas of damp or trickles of water in case you have a leak in the hull. Just for information I had a similar experience on my boat, except the cooling system did not overflow, and even though I am supposed to know a little about boats it took me a couple of months to finally identify the hull leak. However this was on a 20 year old boat, hence wanting to know more about your situation. Tony Brooks

spickard
spickard

Posted: Thu Feb 09, 2012 8:26pm

Post Subject: BMC Thornycroft 4 cylinder diesel

Sorry Tony, I have read the original question and agree is lacking information. Firstly my boat is a 27ft fibreglass full displacement type with BMC motor. The previous owner estimated over 2000hrs on the engine and since it is 24yrs old I dont have any reason to doubt that figure. The cooling system uses raw water through a filter into the engine and is discharged through the exhaust. As you have already quessed I have little experience of this kind of cooling and the reference to radiator cap was incorrect, the cap is on the heat exchanger. Your persistance with me is appreciated

Tony-B
Tony-B

Posted: Fri Feb 10, 2012 7:53am

Post Subject: BMC Thornycroft 4 cylinder diesel

Right, now we have something to work on. I assumed that you meant the pressure cap. The fact that you have a pressure cap and a wet exhaust tells me that you have heat exchanger cooling with only a few litres of coolant in the engine and raw sea/river/canal water being pumped through tubes in the exhaust manifold (heat exchanger) to cool the coolant and then out of the exhaust. I am sorry but your description of the bilge pump running, the limited amount of water in the engine, the fact that a leak from the engine itself should end up in the drip tray rather than the bilge, and the lack of any mention of overheating still leads me to believe that the water that is being pumped out is not coolant. I think it is some sort of raw water (what you are floating in). It it happens with the boat stationary but with the engine running then carefully inspect the whole length of the exhaust hose run - I have known rubber/plastic silencers to burn through. If it happens when you are moving then have a good look at the rudder tube and stock inside the boat. On old GRP boats water can leak up the stock when moving, especially when turning under power. Then it is a question of cleaning and drying the whole bilge and engine drip tray and running the engine to see what is dripping and when. Have a good look at the transom corners (assuming you have a transom stern). These are vulnerable to damage and you may have a hole right through that squats into the water when under power. If you have calorifier hot water it could even be a leaking domestic pressure relief valve or a leak on the plumbing BUT in that case I would have expected you to complain about the domestic water pump running excessively. Tony Brooks

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