Curtis ford has recently revived patent for a diagnostic device that he says will pinpoint the trouble with a car's cooling system-whether it's a faulty head gasket,a clogged water pump or a defective thermostat - and thus help cut down on smog. Even if a car seems to be running fine, Ford said an engine that is running below the correct temperature emits excessive quantities of carbon monoxide and hydro-carbons. An engine running hotter than its ideal temperature emits excessive nigtogen oxide.