C210 PLT TAKES OFF WITH ENG COWLING PLUGS IN PLACE AND RETURNS FOR EMER LNDG.

Narrative

FLEW INTO SAT ARPT THE PREVIOUS DAY. WAS UNLOADING BAGS AND FOUND ENG COWLING PLUGS IN BAGGAGE COMPARTMENT. PUT IN PLUGS. DEPARTED FOLLOWING EVENING AFTER DARK. FORGOT ABOUT PUTTING PLUGS IN (NEVER USE THEM ON THIS OR ANY OTHER ACR) AND DID NOT SEE THEM ON PREFLT. COOL WX RESULTED IN NORMAL RUNUP TEMPS. PWR APPLICATION WAS NORMAL FOR TKOF AND INITIAL CLB. AT FIRST PWR REDUCTION (1000 FT AGL); SCAN SHOWED BOTH CHART AND OIL TEMPS AT TOP OF GREEN AND CLBING. A MOMENT'S THOUGHT BROUGHT THE RECOLLECTION OF THE PLUGS. AT THAT POINT; I WAS RIGHT AT THE BASES; TRAVELING AWAY FROM THE ARPT. I IMMEDIATELY TURNED 90 DEGS TO THE R; AND DSNDED TO APPROX 600 FT AGL; THEN INFORMED ATC OF WHAT I WAS DOING AND DECLARED AN EMER. TOLD ATC I HAD AN OVERHEATING ENG. WITH PWR REDUCED AND IN VMC; ATC GAVE A VECTOR TO THE ARPT FOR A VISUAL/CONTACT APCH. APCH WAS MADE WITHOUT INCIDENT; TAXIED TO FBO. DIGITAL OIL TEMP GAUGE NEVER WENT OVER 260 DEGS; CYLINDER HEAT TEMP NEVER WENT OVER 460 DEGS AFTER ALLOWING ENG AND OIL TO COOL. OIL LEVEL CHKED OK; SMELLED NORMAL; REMOVED PLUGS AND MADE NORMAL FLT. HUMAN FACTORS -- LACK OF CONCENTRATION DURING PREFLT AND ABNORMAL USE OF THE COWL PLUGS COULD HAVE LED TO DISASTER. I HAVE DEVELOPED WHAT I CONSIDER A GOOD SCAN THAT CAUGHT THE PROB BEFORE THE ENG OVERHEATED AND SEIZED. WAS VERY FORTUNATE THE WX (VISIBILITY IN PARTICULAR) HAD IMPROVED FROM THE 500 FT; 3/4 MI VISIBILITY IT WAS EARLIER IN THE DAY.