check for blockages where small hose fits on expansion tank , and engine /cyl head.[they tend to get blocked with rust and cause airlock] this is providing you have ruled out previous fixes to your question
k
June 2010
feel top hose check thermostat is opening,make sure expansion tank is not pressurising and check for bubbles in coolant,is your fan working?could be head gasket
wickham
June 2010
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