Narrative:

While at 2000 ft over rapid river, I noticed the temperature gauge approaching red line. I immediately looked for a field to land on. The closest large enough field that appeared suitable on short final I noted it was water soaked with puddles and aborted the attempt. On pulling away from the field on full power I again noted I was nearly red lined on the temperature gauge. Us 2 which runs northeast from gladstone to rapid river is a 4 lane divided highway with light traffic. Knowing I could not make the escanaba airport which was about 12 mi further south, I elected to land on the highway. After landing safely, I shut down the engine and pushed the plane's tail over the shoulder with the wings parallel to the shoulder and clear of the highway. Inspection of the engine revealed I had failed to remove the cowl plugs which prevented air cooling. The solution is obvious -- remove cowl plugs before flying. Also, attaching red ribbons to the cowl plugs will assist in noting they are still in the cowl. After cooling the motor, the state police on hand held back the traffic and the takeoff and return to the escanaba airport was uneventful. My local mechanic checked the motor and found no problems. I believe my prompt action in landing and not trying to make the airport kept the engine from seizing and possibly having to land where there was no suitable place to do so. Lesson learned: be more observant on preflight.

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Original NASA ASRS Text

Title: SMA WITH SPI HAS ENG OVERHEAT. FORCED LNDG ON HWY. CAUSE: FAILURE TO REMOVE COWL PLUGS.

Narrative: WHILE AT 2000 FT OVER RAPID RIVER, I NOTICED THE TEMP GAUGE APCHING RED LINE. I IMMEDIATELY LOOKED FOR A FIELD TO LAND ON. THE CLOSEST LARGE ENOUGH FIELD THAT APPEARED SUITABLE ON SHORT FINAL I NOTED IT WAS WATER SOAKED WITH PUDDLES AND ABORTED THE ATTEMPT. ON PULLING AWAY FROM THE FIELD ON FULL PWR I AGAIN NOTED I WAS NEARLY RED LINED ON THE TEMP GAUGE. U.S. 2 WHICH RUNS NE FROM GLADSTONE TO RAPID RIVER IS A 4 LANE DIVIDED HWY WITH LIGHT TFC. KNOWING I COULD NOT MAKE THE ESCANABA ARPT WHICH WAS ABOUT 12 MI FURTHER S, I ELECTED TO LAND ON THE HWY. AFTER LNDG SAFELY, I SHUT DOWN THE ENG AND PUSHED THE PLANE'S TAIL OVER THE SHOULDER WITH THE WINGS PARALLEL TO THE SHOULDER AND CLR OF THE HWY. INSPECTION OF THE ENG REVEALED I HAD FAILED TO REMOVE THE COWL PLUGS WHICH PREVENTED AIR COOLING. THE SOLUTION IS OBVIOUS -- REMOVE COWL PLUGS BEFORE FLYING. ALSO, ATTACHING RED RIBBONS TO THE COWL PLUGS WILL ASSIST IN NOTING THEY ARE STILL IN THE COWL. AFTER COOLING THE MOTOR, THE STATE POLICE ON HAND HELD BACK THE TFC AND THE TKOF AND RETURN TO THE ESCANABA ARPT WAS UNEVENTFUL. MY LCL MECH CHKED THE MOTOR AND FOUND NO PROBS. I BELIEVE MY PROMPT ACTION IN LNDG AND NOT TRYING TO MAKE THE ARPT KEPT THE ENG FROM SEIZING AND POSSIBLY HAVING TO LAND WHERE THERE WAS NO SUITABLE PLACE TO DO SO. LESSON LEARNED: BE MORE OBSERVANT ON PREFLT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.