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wilsonian...
wilsonian...

Posted: Thu Nov 10, 2011 7:24pm

Post Subject: Water loss

I have recently purchased a 6 year old narrow boat fitted with a 4 cylinder 45 Barrus Shire engine. The engine had only done 150 hours, however the core plugs had to be replaced due to leakages (frost damage?). This was completed before purchase. I have since added almost 200hours to the engine. It uses no oil and runs cool and there are no obvious signs of water leaks. But I have to top up the expansion tank every 8 hours or so of cruising. Any thoughts would be very welcome on how to sort this water loss out Ian

Tony-B...
Tony-B...

Posted: Fri Nov 11, 2011 8:05am

Post Subject: Water loss

First there are a couple of things about the question that need clarifying. The first is if the engine runs cool how do you know it needs topping up after 8 hours running? Indeed it is dangerous to remove the pressure cap from a hot engine. I suspect that you really mean that you top the engine up each morning when the engine is cold again. The second thing is that I would rather like to know more about this "expansion tank". Are you talking about the filler on the engine or a separate tank, often plastic. If the later how large is it? It would also be helpful if you confirmed that we are talking about a boat with skin tank cooling. Assuming that you are talking about topping up every morning then I suspect that you are simply over filling it. The volume of water in a narrowboat's cooling system is totally unknown because the volumes of skin tanks differ as do the use or not of as calorifier and the lengths of hose runs. This means that any "rule of thumb" one may have used for a car or any mark on the header tank (which was probably made for a vehicle with a known coolant capacity) is most likely to be wrong. First of all bleed the skin tank and manipulate any bends in hoses that might trap air so the air can find its way to the skin tank or expansion tank. This is important because air in a system expands more than water. Fill the expansion tank to well above the maximum mark or to the brim in the case of a filler in the exhaust manifold and get the boat right up to running temperature. Coolant will be blown out of the overflow as the system heats up and causes the coolant to expand. Next morning note the water level and only top up to this level. It will be the correct one for the boat. It is possible that the freezing may have internally cracked something like the exhaust manifold so water leaks into the exhaust gasses but it is far less likely that the overfilling. If I am wrong I think you will need a cooling system pressure tester to pressurise the cold system without the engine running to locate any leak that you can not find with the engine hot and pressurised. Tony Brooks

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