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loss of coolant fluid

My isuzi 35hp has just started to loose coolant fluid. The engine does not show overheating. It has 550 engine hours. Recently completed a 2 week holiday with no problems. After 2 weeks without running we now have a large puddle of coolant under the engine after 1 hours use. Why might this have just suddenly started and what may be the causes? How can I fix it? thanks Heather.

Asked by: heather dawes  | 6.50pm, Friday 25 October

WW says:

Coolant leaks can come from several sources. Firstly, leaks from hoses may occur, although you should be able to trace this by inspecting each flexible hose once the engine has come to temperature (with CARE: they may be at 85C or hotter).
Another possibility is that an air lock has forced coolant out of the system- it may be worth bleeding the skin tanks (there should be a screw or valve to allow air out).
a similar air lock can occur within calorifier heating hoses, as these can sometimes reduce circulation, build up an air lock and then cause coolant loss.
If you have recently topped up the engine, is the coolant mix proper strength- or has it been topped up with just water? Dilution of the coolant lowers the effective boiling point, which can lead to boiling over.
You may also find thatif you completely top up the system, then you may lose a litre or two when the system warms up, from the expansion of the coolant; this happens especially if you do not have an expansion tank fitted.
It may also be that the pressure cap on the engine header tank and/or the coolant tank on the engine may have failed, so when pressurised, the coolant flows out from the over-pressure fitting. You can add a plastic pipe to this and run it to a plastic milk carton, or similar, to see if this is the cause.
Other causes include flexible pipes internally delaminating, so causing pressure increase, and also the engine thermostat failing shut, which could cause localised overheating and coolant loss.
If we can be of any more help, please let us know.

Mark Langley  | 5.35PM, Monday 28 October

Readers say:

If you have a calorifier using hot water from the engine, the hoses to the calorifier will almost cerrtainly be connect to adapters that screw into the cylinder block or head. There may be leakage round the threads. You can try tightening them, or removing them, cleaning up the threads and the threads in the engine and refitting them using plenty plumbers' PTFE tape. Another problem, and this is not nice, is failure of the seal on the water pump.

John Spicer  | 10.35AM, Wednesday 30 October

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