have the cooling system pressure tested or buy a new pressure cap with the engine running WATCH the EXPANSION bottle run engine up to normal check all hoses for drips check for any brown water stains around the water pump gland seal on the pipes or block area if the expansion bottle bubbles VIOLENTLY AFTER A TIME SUSPECT HEAD GASKET PROBLEM.you should NOT HAVE TO KEEP FILLING up a SEALED SYSTEM once filled and bled .
wirecutterman, February 2008
