PLT OF AN ATX BEECH BE58 RETURNED TO LAND AFTER BOTH ENGS' TEMPS WERE RAPIDLY INCREASING TO THE RED LINE.

Narrative

AS I CLBED THROUGH ABOUT 4000 FT MSL; WHILE DEPARTING SUE; I NOTICED BOTH ENG TEMPS OF MY BE58 RAPIDLY INCREASING TOWARD RED LINE. I HAD BEEN CLRED BY GRB APCH TO CLB AND MAINTAIN 6000 FT AND CONTACT ZMP. I IMMEDIATELY REDUCED PWR AND LEVELED OFF AT ABOUT 4500 FT MSL. I QUICKLY NOTED THE OUTSIDE AIR TEMP TO BE -16 DEGS C AND THE ENG COWL FLAPS TO BE FULLY OPEN. I THEN CHKED IN WITH ZMP AND INFORMED THEM THAT I NEEDED AN IMMEDIATE TURN AND DSCNT TO LAND BACK AT SUE. I BEGAN MY L TURN AND DSCNT AS I WAS GETTING CLRNC TO DO SO. CTR ASKED IF I WAS DECLARING AN EMER AND I RESPONDED 'NEGATIVE AT THIS TIME. I HAVE AN ENG TEMP PROB THAT SEEMS TO BE UNDER CTL AT A GREATLY REDUCED PWR SETTING.' SHORTLY AFTER THIS; I WAS SWITCHED BACK TO GRB APCH AND CLRED FOR THE VISUAL INTO SUE. I CANCELED MY IFR FLT PLAN ON SHORT FINAL TO RWY 27 AT SUE. ONCE ON THE GND AT SUE; I ADVISED GRB APCH; AS THEY HAD REQUESTED AND TAXIED TO THE RAMP. I SHUT DOWN THE ENGS; GOT OUT AND INSPECTED THE ACFT. UPON INSPECTION; I FOUND THAT THE HOMEMADE COWLING PLUGS; WHICH WERE NONSTANDARD; HAD NOT BEEN REMOVED DURING PREFLT. (BY NONSTANDARD; I MEAN THAT THEY WERE NOT RED AND HAD NO VISUAL INDICATIONS FROM THE COCKPIT OF THEIR PRESENCE IN THE COWLING.) I BELIEVE THAT THIS WAS A MAJOR FACTOR IN MY FAILURE TO NOTICE THAT THE COWLING PLUGS WERE STILL IN THE COWLING.