On April 25, 1999, at 1007 hours Pacific daylight time, a Beech 36TC, N36MN, collided with a vehicle while attempting a forced landing on the shoulder of interstate highway 15 near Lake Elsinore, California. The forced landing was precipitated by a loss of engine power while in cruise. The aircraft was owned and operated by the pilot under 14 CFR Part 91 of the Federal Aviation Regulations. The aircraft incurred substantial damage and the vehicle minor damage. The private pilot, the sole occupant, was not injured. There were no injuries to persons on the ground. The personal flight originated at 0900 as a round robin cross-country from Chino to Thermal, California, and was returning to Chino when the accident occurred. In a telephone interview with the Safety Board on April 26, the pilot reported that he was returning to Chino from Thermal when the engine smoothly quit. He switched fuel tanks, turned on the electric boost pump and attempted to obtain a restart, without success. As the aircraft descended, he selected a clear area on the shoulder of the interstate highway for a landing. Nearing touchdown, he had to maneuver to avoid a highway sign and the right wing contacted the back of a pickup truck. The pilot further reported that as the aircraft touched down, the engine restarted. During the interview, the pilot stated that the aircraft had been in a local paint shop for the past 60 days for repainting. This was the first flight after the aircraft was picked up. When he departed from Chino on the outbound leg, the pilot used the right fuel tank because the fuel indicators showed it to be the fullest tank. The 20-minute flight to Thermal was uneventful and the pilot shut down the engine after landing. The pilot was on the ground 10 minutes, then restarted the aircraft for the return flight to Chino. The engine start and flight was accomplished on the left fuel tank because the fuel gage showed it to be 3/4 full while the right indicated 1/2 tank. The pilot stated that he performed a thorough engine run-up before takeoff from Thermal and that the flight to the point of power loss was uneventful. The aircraft was recovered without the necessity of disassembly or disturbance to any aircraft system. A Federal Aviation Administration airworthiness inspector from the Riverside, California, Flight Standards District Office examined the aircraft at the recovery facility. The fuel tanks and lines were intact with no evidence of leakage. One pint of fuel was drained from the left tank while the right tank contained 15 gallons. The fuel vent lines for the left tank were clear. The rear vent lines for the right tank were also unobstructed. The forward vent line for the right tank was found plugged with insect debris and dirt. Further examination of the forward right tank line revealed that it was disconnected at the B-nut, which connects the line to a check valve and open to atmosphere inside the wing. The fuel indicating system was examined by powering up the aircraft electrical system and manipulating the float sensors in the tanks. The right tank sending unit and cockpit gage was found to be accurate. The left tank sending unit and gage displayed erratic indications of quantity. On initial power up the left tank gage displayed 3/4 tank. Subsequent shutdowns and power ups of the system yielded tank quantity indications of 1/4, full, and 3/4 again. No discrepancies were noted with the engine. In his written statement, the pilot reported that prior to the accident he had not used a dipstick or other qualitative observational method the accurately determine the fuel load on the airplane, but rather used a method relying on the gages and consumption calculations.