On September 3, 2002, about 1200 eastern daylight time, a Piper PA-18, N5428H, operated by Aerial Sign Company of Hollywood, Florida, was substantially damaged during a forced landing in Belmar, New Jersey. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the flight that departed Allaire Airport, Belmar, New Jersey. No flight plan had been filed for the positioning flight that was conducted under 14 CFR Part 91. According to the pilot, the airplane was used for banner towing and was being repositioned to Hollywood, Florida, with intermediate stops at Norfolk, Virginia, and Myrtle Beach, South Carolina. The pilot departed on runway 32, and performed a right downwind departure. He switched fuel tanks while climbing, and leveled the airplane at 1,200 feet mean sea level (MSL). As the airplane neared the coast line, the engine "smoothly" lost power. The pilot turned the airplane back toward the departure airport. However, he was unable to restore engine power, and set up for a forced landing in an open field. On final approach, he saw the field was uneven, and turned the airplane to land in a soccer field. The airplane touched down without incident; however, due to people on the right, a building straight ahead, and a chain link fence to the left, the pilot turned the airplane to the left. The airplane struck the fence and came to rest on its nose. The pilot reported that the airplane had 3 fuel tanks, each with a capacity of 18 gallons. One was located in the left wing, and two were located in the right wing. During his preflight inspection of the airplane, he noticed that the fuel in one tank was pink in color. He attributed that to the addition of a fuel additive. The fuel in the other tanks were blue in color. Departure was made on the left wing tank, and he switched to the right inboard tank on the climb. According to an inspector from the Federal Aviation Administration (FAA), the left elevator was crushed and bent, the left wing struts were bowed, and the firewall was wrinkled. He reported that the fuel in the left wing tank, the carburetor, and the main fuel strainer was red in color, and had an oily feel when touched. In addition, the fuel selector was checked and found to operative with no blockage; the main fuel sump was not blocked; no problems were noted with the carburetor float, and the main jet on the carburetor was absent of debris. Although the pilot and FAA inspector did not report the same fuel tank as containing the red colored fuel, both were in agreement that the one tank contained the red colored fuel. The operator told the FAA inspector that the red color was from an additive placed in the fuel tank, at a rate of one quart for each refueling. Examination of the engine revealed low compression on all cylinders, ranging from 44/80 to 5/80. Air bypass was noted on all exhaust valves, and on two of the intake valves. The number two cylinder was removed, and evidence consistent with detonation was found on the surface of the piston, and on the valves. According to the FAA inspector, the additive that was added to the fuel was Marvel Mystery Oil. An empty 1 gallon can of Marvel Mystery Oil was found in the operator's trash. Instructions found on the can stated that the correct ratio for mixing with fuel was 1 part additive to 100 parts fuel. The contents of Marvel Mystery Oil were 74 percent mineral oil, 25 percent stoddard solvent, and 1 percent lard. In a telephone interview, the pilot reported that the manager of Aerial Signs told him that the oil had been added. The Chief Pilot reported that there were no specific procedures for the use of Marvel Mystery Oil, no written direction, and it was not being used anymore. The Manager of Aerial Signs reported that he had told his pilots to not use Marvel Mystery Oil any more. In addition, he talked to the mechanics, and they had not added it and the pilot reported that he had not added it. According to Lycoming Service Instruction No. 1014M, dated May 22, 1995, the use of fuel additives was not recommended, and voided the engine warranty.