C152 PLT RPTS SMOKE IN HIS COCKPIT THEN LANDS SAFELY.

Narrative

ON WEDNESDAY I TOOK OF FROM ZZZ TO PRACTICE SOME COMMERCIAL MANEUVERS OUT IN THE ZZZ AREA. AFTER FINISHING OUT MY MANEUVERS; I DECIDED TO HEAD BACK HOME TO ZZZ. WHILE HEADING BACK TO ZZZ I CALLED TWR AND NOTIFIED THEM THAT I WAS 10 MILES FROM THE NORTH INBOUND AT 3;000 FT MSL WITH ATIS AND THAT I REQUEST ANY OPTION. I WAS CLEAR FOR THE OPTION AND WAS TOLD TO COME IN FOR A RIGHT DOWNWIND FOR RUNWAY 24. AS I WAS TURNING FOR A RIGHT DOWNWIND FOR RUNWAY 24; 3 MILES FROM ZZZ SMOKE APPEARED IN MY COCKPIT. I THEN PROCEEDED ON CHKING MY WINGS; GAUGES; AND ALL MY INSTRUMENTS TO SEE FOR ANY TRACES OF FLAMES; THERE WERE NONE. I THEN TOLD TOWER; 'C152 HAS SMOKE IN THE COCKPIT; REQUESTING A STRAIGHT IN FOR RWY 6.' TWR THEN REPLIED TO ME; 'C152 WILL YOU NEED ME TO SEND OUT THE FIRE TRUCKS?' I THEN REPLIED; 'NO THIS IS NOT AN EMER. SMOKE HAS APPEARED IN MY COCKPIT AM OK AND I STILL HAVE CTL OF THE ACFT.' TWR THEN REPLIES; 'OK I AM STILL GOING TO SEND OUT THE TRUCKS FOR YOU AND YOU ARE CLRED TO LAND ON RWY 6.' I LANDED ON RWY 6 AND AFTER LNDG; I CALLED TOWER AND SAID; 'ZZZ TWR MAY I TAXI ON TXWY A AND BACK TO THE WEST RAMP.' TWR REPLIES; 'C152; NO. I PREFER YOU SHUT THE ACFT OFF AND LET THE FIRE DEPARTMENT TAKE A LOOK AT THE ACFT.' I THEN REPLIED; 'C152 SHUTTING DOWN. THANKS.'CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE SMOKE APPEARED IN THE COCKPIT SHORTLY AFTER TURNING ON THE HEATER. POST FLT INSPECTION REVEALED THAT OIL HAD BEEN SPILLED DURING SERVICING AND HAD GOTTEN INTO HEATER MANIFOLD.