first and foremost do you have plenty coolant in your reservoir,as you have given no veh.details would check the thermostat is opening ok,if that means removing and testing in hot water then that is better than a ruined engine,is there water circulating in your reservoir,if not the water pump may be shot,is there a lot of pressure when you remove the reservoir cap?may point to a head gasket,these are some checks you could do.
cdc, August 2011
