What was found
PILOT / CREW REPORTED SMOKE AND SMELL IN CABIN AFTER TURNING ON AIRCRAFT HEAT TO DEFOG WINDSCREEN. CORRECTIVE ACTION, INSPECTED BOTH ENGINES AND HEATER MIXING VALVE FOR OBVIOUS DEFECTS, NONE NOTED. HAD PILOT RUN BOTH ENGINES AND TURN ON BLEED AIR FOR HEAT. NO SMOKE SEEN, BUT A SLIGHT SMELL IN CABIN. SMELL DISSIPATED OVER TIME. SMELL CAME FROM ENGINE WASHES OVER TIME AND THE LACK OF USE OF AIRCRAFT, HEAT DUE TO SUMMER WEATHER. PILOT WAS SATISFIED WITH FINDINGS AND OUTCOME. RETURNED AIRCRAFT TO SERVICE.