On July 21, 2000, at 1320 hours Pacific daylight time, an amateur-built Steel Rans RV-6, N64ME, nosed over during a forced landing at the Winnemucca, Nevada, airport. The forced landing was precipitated by a loss of engine power. The airplane, owned and operated by the pilot under 14 CFR Part 91 of the Federal Aviation Regulations, sustained substantial damage. The private pilot, the sole occupant, sustained minor injuries. Visual meteorological conditions prevailed and a flight plan was not filed. The flight departed the Winnemucca airport about 1230 and was en route to Elko, Nevada. In a telephone interview, the pilot reported that the flight left the San Francisco Bay area earlier in the day and was en route ultimately to Oshkosh, Wisconsin. In the area of Winnemucca, the pilot observed that the engine oil temperature was nearing the upper red line limit and she landed at Winnemucca for it to cool off. After about an hour on the ground, the pilot performed a detailed preflight inspection and run-up, with no abnormalities detected. The pilot then elected to depart Winnemucca and fly to Elko. About 10 minutes after departure, the engine oil temperature began to climb once more to the red line limit and the pilot decided to turn around. After reestablishing a course toward Winnemucca, the oil temperature exceeded the red line limit and the engine began to lose power. The pilot reduced the throttle and set up for a landing on a highway and the engine power returned. The pilot then attempted to continue to Winnemucca and the engine lost power short of the airport. The pilot said she was able to reach the runway, but was too low to make any traffic pattern maneuvers, and too high to land normally. The pilot reported that she was slightly fast and touched down near the halfway point on the runway, and was unable to stop prior to overrunning the pavement end. The airplane encountered soft, sandy soil and nosed over. According to the aircraft owner, following recovery of the aircraft, the engine was disassembled and inspected at Giles Engines in Reno, Nevada. The purpose of the disassembly was to inspect the engine for sudden stoppage damage and repair it for return to service. Disassembly disclosed that the vernatherm had not been installed in the engine and the oil supply was bypassing the oil cooler. The records disclosed that the engine was built-up about 90 hours prior to the accident by a firm which specializes in performance improvement rebuilds for the experimental aircraft market. The engine is a basic Lycoming IO-360 with several modifications for power improvement.