Narrative:

Shut down engine enroute due to oil discharge. Shortly after reaching cruise altitude of 5500 ft a large amount of oil was observed flowing over the right engine cowling. I immediately diverted to closest airport. While enroute I observed the engine was still operating within normal temperature and oil pressure limits; but I was concerned the engine would eventually stop and/or the oil might ignite on the hot exhaust system so I chose to shut down and feather the right engine. I continued uneventfully and landed. The local a&P checked the engine which still contained 8 quarts of oil. The source of the oil turned out to be a loose oil fill cap. After adding 4 quarts of oil; we test ran the engine; it was developing full power and operating normally. Since the shut down occurred before any abnormal temperatures or performance was observed; it was determined that no damage had occurred. I did not declare an emergency; however I had tuned in the nearest ATC frequency just in case I needed to call for assistance. I also tried to raise the local unicom to let them know I was coming; but I couldn't raise them. When I added a quart of oil to the right engine just before departure; I believe that I forgot to put the cap back on. My standard practice is to lay the fill cap/dip stick on top of the cowling so I don't forget it; however on this airplane the dip stick and oil fill cap are separate. The oil fill cap is on a short chain attached to the engine. When loose; the restraint keeps from losing the cap; but it also keeps it out of sight. Likely this deviation from habit contributed to my failure to properly secure the cap.

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Original NASA ASRS Text

Title: A C310 reported losing oil from the right engine. He shut down the engine and diverted to the nearest suitable airport; where he discovered he had failed to secure the oil fill cap.

Narrative: Shut down engine enroute due to oil discharge. Shortly after reaching cruise altitude of 5500 FT a large amount of oil was observed flowing over the right engine cowling. I immediately diverted to closest airport. While enroute I observed the engine was still operating within normal temperature and oil pressure limits; but I was concerned the engine would eventually stop and/or the oil might ignite on the hot exhaust system so I chose to shut down and feather the right engine. I continued uneventfully and landed. The local A&P checked the engine which still contained 8 quarts of oil. The source of the oil turned out to be a loose oil fill cap. After adding 4 quarts of oil; we test ran the engine; it was developing full power and operating normally. Since the shut down occurred before any abnormal temperatures or performance was observed; it was determined that no damage had occurred. I did not declare an emergency; however I had tuned in the nearest ATC frequency just in case I needed to call for assistance. I also tried to raise the local Unicom to let them know I was coming; but I couldn't raise them. When I added a quart of oil to the right engine just before departure; I believe that I forgot to put the cap back on. My standard practice is to lay the fill cap/dip stick on top of the cowling so I don't forget it; however on this airplane the dip stick and oil fill cap are separate. The oil fill cap is on a short chain attached to the engine. When loose; the restraint keeps from losing the cap; but it also keeps it out of sight. Likely this deviation from habit contributed to my failure to properly secure the cap.

Data retrieved from NASA's ASRS site as of April 2012 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.