On December 8, 2011, about 1530 eastern standard time, a Curtiss Wright P40M airplane, N5813, impacted a fence during a forced landing and a runway excursion, following a loss of engine power, at Clermont County Airport (I69). The pilot sustained minor injuries. The airplane sustained substantial damage to both wings and the horizontal stabilizer. The airplane was registered to and operated by the Tri-State Warbird Museum under the provisions of 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight originated from I69 about 1440. The World War II era airplane was recently restored and had accumulated approximately 5 hours since it had been returned to an airworthy condition. The airplane was originally manufactured in May 1943. The pilot reported that he had completed maneuvers in the local area prior to the accident. He stated that while returning to the airport, the engine shuddered several times and the oil pressure dropped to zero. Approximately 20 seconds later, the engine failed completely. About that time, the windshield and canopy were covered with oil and coolant restricting forward visibility. The pilot was able to execute a forced landing to the airport; however, he was unable to stop on the available runway. The airplane subsequently departed the end of the runway and impacted the airport perimeter fence. A postaccident inspection revealed that the engine oil cooler exhibited a crack adjacent to a thermostatic bypass valve. The oil cooler was an original World War II era component. The crack did not appear to have initiated at a previously repaired area.