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Posted: Wed Sep 22, 2010 7:44pm

Post Subject: water level

Hi Tony when the engine has been running for awhile yes the water level goes down in the header tank but when i stop the engine and remove the cap the water bubbles back up to max level any ideas thanks john


Posted: Thu Sep 23, 2010 8:42am

Post Subject: water level

Modern cooling systems run under the pressure created by expansion of the coolant. It is typically 6 or 15 psi. When you remove the cap this pressure is lost. Therefor it seem this pressure is pushing the coolant somewhere. First of all ensure the skin tank (I assume this is on a typical narrowboat - you do not say) is thoroughly bled in case its contains gas that is being compressed. Normally air tends to cause a loss of coolant because it expands more than water thus filling the expansion tank. Next check all the "rubber" hoses in case any have gone soft and are being "blown up" by the pressure. It is not unknown on BMCs with Polar exhaust manifolds for the rubber end caps to "blow up" when hot - and then burst! That is all I can think of. Tony Brooks

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