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akbutler
akbutler

Posted: Mon Dec 04, 2017 1:52pm

Post Subject: Cooling System Pressure

I am looking at a boat with a marinised Ford diesel. As a "marine" person the cooling system looks very strange to me. There is a Bowman manifold exchanger but the tube bundle is blocked off both ends so it isn't actually working as a heat exchanger, just a header tank and manifold cooler. The water from the engine passes into a large tank welded to the hull plating where the water is cooled by the water outside. The cap on the Bowman was leaking and releasing all pressure to a plastic overflow tank. It works OK but the new Bowman pressure cap is 10psi which means that the cooling tank would also operate at 10psi which seems a lot for a flat sided tank. Is this a typical canal boat installation? Thanks

Tony-B
Tony-B

Posted: Mon Dec 04, 2017 2:12pm

Post Subject: Cooling System Pressure

If this is a Ford XLD (OHC) engine please think very carefully about the result of a cam belt snapping or the belt rusting itself to the lower pulley/sprocket over the winter when it is then started. Now the question. The basic set-up sounds absolutely standard for a skin tank cooled boat. Probably 95% of narrowboats are cooled like that. However there might be a question over the skin tank being fit for purpose but I can not comment without seeing it. I take it that you mean the filler/pressure cap is leaking and not one of the rubber caps on the end of the manifold/header tank assembly. If it is an end cap leaking come back to me. The next step is to decide how the plastic header tank has been connected. I am going to assume its by the small overflow pipe that is normally just below the filler/pressure cap. If it is not please come back. I am not sure exactly what you mean by "the cap on the Bowman was leakingThe cap on the Bowman was leaking and releasing all pressure to a plastic overflow tank and releasing all pressure to a plastic overflow tank". Under normal operation expanding coolant will flow into the plastic tank as the engine heats up while maintaining pressure in the cooling system. If the filler/pressure cap on the manifold is one with a rubber seal rather than a brass disk immediately under the top of the cap then as the engine cools coolant from the plastic tank will get sucked back into the engine. If its an ordinary filler/pressure cap then as it cools it will just suck air back into the engine. An alternative arrangement is to fit the pressure cap on the plastic tank and a plain cap with rubber seal but no springs on the manifold. That would operate as above. Cars tend to operate at 15psi and have you seen the thickness of the brass radiator parts? As the manifold is marked Bowman its probably cast aluminium and will be plenty strong enough. If this is not clear enough please email photos of the plastic tank, its piping, a general view of the engine and the cap(s) to Tony@tb-training.co.uk together with what is unclear.

akbutler
akbutler

Posted: Tue Dec 05, 2017 10:29am

Post Subject: Cooling System Pressure

Tony, thank you so much for your reply and invaluable information. The engine is indeed OHC and I share your cambelt concerns. I came to this boat to help its lady (liveaboard) owner as it had a well-blown head gasket and several other issues. Obviously I fitted a new cambelt as I had no history for it. It runs very well despite a serious overheating session when the gasket blew. The tube bundle caps are OK, it's the pressure cap lower seal which should retain pressure that was leaking so water was just running to the expansion tank without building up pressure. The cap is the type with an upper rubber seal and the vent to the expansion tank is in the usual place between the seals so it is a closed system and will suck water back. I am much happier with your advice. many thanks, Alan

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