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Calorifier issue

I have a Kelvin J3 with an non-pressurised, skin tank cooling system. There's a header tank on the engine-room bulkhead, about a gallon capacity, with a removable lid. Normally the tank is about half full when cold and about three-quarters when hot. Recently the coolant level has been increasing when check cold on successive mornings during boating and after a few days eventually overflows when hot. The domestic water system has a twin coil calorifier, one fed from the engine and one from the Alde. The boat is 20 years old and the tank has a strap on jacket, not a foam-sprayed one. My suspicion is that the engine heating coil in the tank is failing and that domestic water in the tank is getting into the engine circuit when the domestic pump is operating. I can't think how else additional water is getting introduced into the engine cooling system. Would this concur with your view, or can you think of anything else that would cause this symptom. Regards Colin

Asked by: Colin Bigmore  | 9.51am, Monday 5 November

WW says:

It certainly does sound like a possibility that the domestic water is leaking into the engine coil- this then mean that your domestic water may be contaminated with engine coolant (and antifreeze- not very healthy!).
You may be able to drain down the calorifier and isolate it, assuming it has isolation valves from the cold water intake, or if you can isolate the engine coil side, running the engine will then indicate if the calorifier is adding to the water in the engine circuit.
Either way, isolating the calorifier from the the engine will give you a more definate answer.
Another alternative is that the skin tank is leaking, which can draw more water into the system, though (hopefully) its unlikely.
If you have recently filled the system with antifreeze and/or water, it is possible that airlocks have formed, which are now pushing out coolant, so it might be worth bleeding the skin tanks just to be sure- however, the volume you mention might not be caused by this. It is worth a quick check though, as any air in the skin tanks can cause a large volume change in the system as it heats up.

Mark Langley  | 10.31AM, Monday 5 November

If your engine installation includes flexible hoses, another possibility is that the hoses might be failing. Sometimes the layers can separate, this will occur most when the water is hot, reducing the volume of the pipes and the cooling system itself. If the pipes are getting restricted the water might get hotter and thus expand more during running causing the tank to overflow.
If the calorifier coil is failing, leaving the domestic water pump on to keep the water system pressurised might produce a detectable rise in the engine coolant over a few days.
I do not think canal water is entering the system, as external skin tank holes will cause loss of coolant rather than increasing the volume.

Rupert Smedley  | 3.55PM, Tuesday 6 November

Readers say:

Many thanks. The difficulty with isolating domestic from engine by either draining down the domestic water in the cylinder or short circuiting the engine coil is that it takes 3-4 days engine running to increase the header tank content to overflowing, so would be difficult to detect now I'm back on my mooring.
Also if transfer is taking place when the water pump is pressuising the domestic system one might expect the pump to cycle periodically especially when the taps are closed and the system under the most pressure.
Historically I've not had problems bleeding the engine cooling system, both swim tanks have bleed valves and it normally purges air with one round of bleeding. Also I've boated about 8 weeks since the engine cooling system was last refilled, this issue has only occurred in the last couple of weeks.
The bilges are dry where the skin tanks are under the boatmans cabin floor unless it's canal water getting! Hopefully not the case especially a Roger Fuller shell.
Not sure if this helps further.

Colin Bigmore  | 11.26AM, Monday 5 November

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