I recently did a head gasket replacement, now I have an issue with my cooling system pulling a vacuum. Replaced the rad. hoses, new thermostat, new temp. sending unit. The Temp. gauge reads hot, but the fans will cut on/off as though it's not really that hot. As long as there is gas being applied, the cooling system circulates, but when it goes back to idling, the hoses are collapsed. Any help would be greatly appreciated.