if the coolant level in your header tank shows correct level then it could be your thermostat is on its way out, take it off and put into a pan of boiling water, if it opens, its ok, if it remains closed or only partly opens then it needs to be changed.when filled with coolant, take it for a run, and this should take out any air pockets, and re-check coolant level.
hope it helps
August 2010
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