Quote:
Originally Posted by kaiser
I have no stream of water from that little pipe either. I think it is one of those issues you should take with a pinch of salt.
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I agree. The small bore pipe from the head to the tank filler neck is there to facilitate head bleeding. This may be either air or super-heated coolant. Air comes out when the head's being filled as part of the coolant refilling process. That can only happen when the pressure cap is not fitted. A small amount of coolant may flow out by squeezing a large hose or when the engine's running because of pressure drop from the pump. However that flow will stop when the pressure cap is refitted. When the hot engine is turned off, the head contents may super-heat, increasing hydraulic pressure in the head. This pressure exists in the small bore pipe and this will lift the relief valve in the cap if necessary. It's a strategy to avoid over-pressurising the full system.
When the pressure cap's in place it's physically impossible for anything to flow through the pipe.
TC