A cold storage distribution center reported that a Mitsubishi FG25 (4G63 LPG engine) forklift started perfectly and ran for 10 minutes, but then the engine lost power and died. Attempts to restart resulted in the engine cranking but not firing. The operator noticed the LPG vaporizer (regulator) was covered in thick white ice.
The technician confirmed the regulator was frozen solid, blocking the liquid LPG from vaporizing into gas. LPG systems rely on engine coolant circulating through the vaporizer to provide the heat required to vaporize the liquid fuel. Without heat, the rapid pressure drop causes the Joule-Thomson effect, freezing the regulator.
He checked the coolant flow to the vaporizer. The inlet hose was warm, but the outlet hose was cold, indicating zero coolant circulation. He removed the inlet hose from the vaporizer and found the internal coolant passages in the vaporizer's aluminum core were completely blocked with a hard, sandy scale-a mixture of degraded coolant silicates and casting sand. The lack of coolant flow prevented heat transfer, freezing the unit.
Furthermore, when he disassembled the vaporizer to clean the coolant passages, he found the "Primary Diaphragm" was torn. The ruptured diaphragm allowed unmetered liquid LPG to flood the secondary chamber, exacerbating the freezing effect and causing the engine to run excessively rich before dying.
The repair involved removing the vaporizer, boiling the aluminum core in a descaling solution to clear the coolant passages, and installing a complete primary and secondary diaphragm rebuild kit. The engine coolant system was flushed, and fresh OAT (Organic Acid Technology) coolant was added. After reassembly, the forklift ran continuously for 2 hours under load with no icing or stalling.
