Posted: Fri Aug 23, 2019 12:05pm

Hi Tony, I need to plumb the two rubber hoses from our marinised engine (Mercedes OM601 diesel) to the calorifier heating coil. We have a central walkway in the engine room with the engine offset to one side and the calorifier to the other (Trad 70ft narrow boat with hydraulic drive). Because of this layout, the route the hoses have to take is around 2.5 metres in each direction. Do you think the engine's water pump will push the water this far or just ignore this circuit and continue to circulate via the skin tank? The marinising pipework is 22mm copper and I'm using 1" internal diameter rubber hoses with 3/4" fittings on the calorifier. Have you seen issues with a long pipe run like this before? Thoughts? Stephen

Posted: Fri Aug 23, 2019 12:30pm

No, some of our Caribbean cruisers must have had equally long pipework because the engine was across the stern and the calorifier under the port gunwale in the back cabin. I do not have sufficient description of your system to get a full picture of it. Some comments - why 22mm copper? If this is in the main cooling circuit then although it may work I think it is a bit on the small side. If this is just for the calorifier then I think it may turn out to eb too large. Normally 5/8" or 1/2" bore hose is used. AS long as the hot feed to the calorifier is taken from the engine side of the coolant thermostat, like form the cylinder head I expect it will work as hoped. If you take the hot feed from the skin tank side of the thermostat then it may not. It could, as you say, allow the calorifier to "short circuit" the skin tank or you may get no flow through the calorifier. I think you need to ensure you have air bleed points at the high point(s) in the calorifier circuit. If you don't you could easily get an airlock and then you would get no calorifier circulation.

Posted: Fri Aug 23, 2019 2:11pm

Thanks for that Tony. Yes, the marinising pipework on the engine from head to exhaust cooler to skin tank to oil cooler and back to the engine block is all 22mm copper. (already installed when I bought the boat). My proposed pipework to the calorifier was chosen to be as unrestricted as possible to aid flow hence 1" hose and 3/4" fittings (the calorifier has 3/4" fittings on it). I've put an auto vent at the high point on the calorifier. Purchasing the hose and fitting it this weekend. I've also installed an electric shut-off valve at the calorifier (I'm being optimistic here) just in case it gets too hot

Posted: Sat Aug 24, 2019 7:17am

I think it will all work OK but two points. Autovent valves may not be as reliable as a manual bleed screw. They have been known to leak over time. The conventional way of dealing with excessively hot calorifier water, and it will be even with a cool engine thermostat, is to fit a thermostatic mixing valve so it blends hot and cold water to give a safe temperature. This has the advantage of drawing less hot water from the calorifierso it stays warm for longer.

Posted: Tue Aug 27, 2019 3:50pm

Thanks Tony, Good information. I'll put it all together and see how it performs. Stephen

Posted: Thu Sep 12, 2019 3:54pm

Hi Tony, Just to report back that everything seems to work just fine. The water circulates via the calorifier as hoped and my electrical shut-off valve prevents the thermo-syphoning of heat from the calorifier back to the engine once it is shut off. Thanks for all the tips Stephen