Event Narrative
A flight that originated in the San Francisco Bay area was en route to Oshkosh, Wisconsin. During cruise, the pilot observed the engine oil temperature approaching the upper limit and decided to land at an airport to allow the engine to cool. After approximately one hour on the ground, the pilot conducted a detailed preflight inspection and engine run-up, which revealed no abnormalities. Departure was then initiated for the next planned stop.
About ten minutes after departure, the engine oil temperature again rose to the red line limit. The pilot elected to turn back toward the airport. Shortly thereafter, the oil temperature exceeded the red line, and the engine began to lose power. The pilot reduced throttle and set up for a forced landing on a highway. The engine power partially returned, prompting the pilot to attempt continuing to the airport. However, the engine lost power short of the facility.
The pilot reported being able to reach the runway but was too low to execute any traffic pattern maneuvers and too high for a normal landing. The airplane touched down slightly faster than normal near the midpoint of the runway and could not stop before overrunning the pavement end. The airplane then encountered soft, sandy soil and nosed over.
Investigation Findings
Disassembly of the engine revealed that the vernatherm—a component that controls oil flow through the oil cooler—was not installed. Its absence allowed the oil supply to bypass the cooler entirely. Engine records indicated that the powerplant had been built approximately 90 flight hours prior to the accident by a firm specializing in performance improvement rebuilds for the experimental aircraft market. The engine was a basic Lycoming IO-360 with several modifications aimed at power enhancement.