> Patrick Griffin wrote:-
> Are you sure the water gets sucked back in when it cools? I can see how
the water gets pushed up into the expansion tank when it expands but the
pressure cap will be closed when the water cools thus stopping the water
---From returning from the expansion tank.
Patrick,
Not trying to teach you how to suck eggs but just in case you are still
unclear on the function of the overflow :-
If you remove the pressure cap on your engine (Rotax 912, 914), you will
note there is a brass coloured round disc in the middle underneath the main
seal. This little disc is like a reed valve. It is spring loaded to keep
it closed in the first instance (check it with your finger nail) and the
pressure build up in the cooling system forces it closed even more. When
the water in the cooling system expands, the main or primary seal is forced
open against the large spring between the cap and the seal and the liquid
flows to the overflow bottle as you have already stated. When things cool
down and the water in the engine and hoses contracts again, atmospheric
pressure on the liquid in the overflow bottle pushes the excess in the
overflow bottle back into the cooling system through that smaller valve in
the middle of the primary seal (or valve) displacing that little valve
against the relatively weak spring tension which is trying to hold it
closed.
I would point out that this system works well when the main seal of the
radiator cap is in good condition. If the main seal is perished or cracked,
when the cooling system cools down, atmospheric pressure is able to force
air through these cracks and into the cooling system leaving the overflow
bottle full. Consequently, in vehicles with this same principle, I have
learned never to trust the radiator is full by confirming there is water in
the overflow bottle. I always now remove the cap and physically check it is
full to the brim as it should be. If the water level is down, there is air
in the system which I'm sure should not be there.
Regards
Kingsley Hurst
Mono Classic 281 in Oz. Bit more done on the rigging of the trailer today.
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