[Healeys] Overheating Healey (closed system)

[Oudesluys]

A closed system is rather the same as a conventional system with an 
overflow bottle. The difference is that in a conventional system the 
overflow bottle is not pressurized while the cooling system is, the 
pressure cap is on the radiator. During expansion coolant will flow to 
the overflow bottle, however when the engine cools down often not all 
coolant is sucked back into the radiator because of the poor sealing of 
the pressure cap. The radiator is usually not filled right up to the 
filler neck and some air is left for expansion.
In "closed" systems there is a  simple or no cap on the radiator, 
without pressure release, the overflow in open connection with the 
bottom of the overflow bottle with the pressure cap on the overflow 
bottle. There should not be any air in the radiator. The overflow bottle 
is fairly large as it has to hold a fair amount of air for expansion and 
for release of pressure without coolant loss. It should be about half 
filled with coolant.
The working pressure is usually a bit higher.

I have converted my cooling system to a semi-closed system using a VW 
overflow bottle but retaining the original 10lbs pressure cap on the 
radiator making sure that it seals absolutely air tight and 
depressurizing the original VW cap of the overflow bottle. I do not 
think the brass radiator can hold the VW pressure of about 22psi. This 
way I keep the radiator  filled 100% at all times.
In the near future I will search for a fitting overflow bottle with a 
conventional pressure cap like on some Volvo's to have a proper 
''closed" system.
Kees Oudesluijs
NL


lists wrote:
> Rick, this means a closed system raises the boiling temp, but the return tank doesn't. It will only ensure escaped fluid to be drawn back into the radiator. Right?
>
> Eric
>
> from	Eric (Rick) Wilkins [e-wilkins at cox.net]	
>
> As coolant gets hot, it expands.  Since the cooling system is sealed,  
> this expansion causes an increase in pressure in the cooling system,  
> which is normal and part of the design.  When coolant is under  
> pressure, the temperature where the liquid begins to boil is  
> considerably higher.  This pressure, coupled with the higher boiling  
> point of ethylene glycol, allows the coolant to safely reach  
> temperatures in excess of 250 degrees.

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