What was found
DURING CLIMB, NOTIFIED OF SOME SMOKE TO THE LT SIDE OF THE COCKPIT NEAR THE DEMISTING VENT. SMOKE SLIGHT & APPEARED TO BE CONTINUOUS. VERIFIED NO VISIBLE FIRE OR SPARKS, & ALL ENGINE PARAMETERS NORMAL. CONFIRMED THE HEATING & DEMISTING KNOBS WERE CLOSED. DIVERTED FOR A PRECAUTIONARY LANDING. LANDING UNEVENTFUL. INSPECTED DUCTING FOR LEAKS OR DAMAGE, NONE FOUND. INSPECTION FOUND SMOKE TO HAVE A BURNING OIL ODOR. INSPECTED ENGINE AREA & FOUND OIL VENTING FROM BLEED AIR VALVE. INSPECTED EXHAUST VENT TUBE. FOUND TUBE HAD A DIME SIZED PIECE OF COKING THAT HAD SEPARATED FROM TUBE INNER WALL & WEDGED OPENING CLOSED. REMOVED TUBING AND CLEANED OUT ALL COKING. REINSTALLED TUBE. PERFORMED COMPRESSOR WASH AND RINSE. PERFORMED OPS CHECK AND LEAK CHECK. RAN ACFT WITH HEATERS & DEFROSTERS ON FOR 20 MINS UNTILL NO SIGN OF SMOKE EMINATED FROM SYS. PERFORMED OPS CHECK FLIGHT WITH HEATERS & DEFROSTERS ON. NO SMOKE. RETURNED TO BASE.