On May 12, 2021, about 1030 Pacific daylight time, a Grumman ACFT ENG COR Schweizer G-164C, N6596K, was substantially damaged when it was involved in an accident near Glenn, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 agricultural flight. The pilot reported that the airplane had just departed with the fuel gauge indicating a half-full tank of fuel and a full load of product (2,200 pounds of rice seed). About 100 ft above ground level the engine lost total power. He saw a narrow dirt frontage road in between rice fields and made a forced landing, during which the airplane landed hard and came to rest upright, causing substantial damage to the wings and fuselage. The pilot reported that he did not refuel the airplane before the accident flight based on the fuel gauge indications. The operator reported that the center fuel tank, which draws fuel from the two wing tanks was empty of fuel. About 1 gallon of fuel was recovered from the fuel sump. The engine and the fuel systems remained intact and uncompromised. Maintenance personnel reported that they checked the fuel gauge in the cockpit, and it revealed that the center fuel tank was indicating half full. When the float connected to an arm in the center tank was manipulated, the fuel gauge in the cockpit moved but not in a manner coincident with the placement of the float, and that the fuel gauge may have been reporting false quantities of fuel. The engine was sent to a repair facility for overhaul with no discrepancies identified. Further testing of the fuel gauge was not accomplished.