Heavy-Duty Diesel Forklift High Temperature Troubleshooting Guide

A 3.5-ton diesel forklift works continuously for heavy loading and unloading of sand and stone materials in a building material processing plant. It triggers water temperature alarms at noon. It runs normally with no load, but the water temperature rises rapidly after only ten minutes of stacking. The driver has to stop and wait for cooling, which seriously delays workshop delivery. How to resolve diesel forklift engine overheating fault?

The maintenance technician did not disassemble the engine directly. Instead, he inspected the diesel forklift cooling system from outside to inside step by step. This troubleshooting logic can be followed for similar faults.

Many overheating problems start with the external radiator, which is often overlooked. When the forklift operates in sandy and dusty environments for a long time, fine dust and sand block the gaps between radiator fins. The airflow is greatly restricted even if the surface only looks slightly dirty. Use a low-pressure air gun to blow along the fins and test the machine after cleaning. If the temperature rises slower but still exceeds the limit under heavy load, there are internal faults.

A loose or slipping fan belt and damaged wind guide cover will reduce cooling air volume. The belt on this forklift was stretched and cracked, and the wind guide cover had cracked edges, causing hot air recirculation. After adjusting belt tension and replacing the broken cover, the air volume returned to normal. However, the temperature was still high under continuous full load, meaning the root cause lies in the cooling circulation circuit.

Then check the thermostat and water pump. A stuck closed thermostat forces coolant to run only in the small circulation loop without passing through the radiator. A worn water pump impeller reduces coolant flow. Both conditions lead to overheating. Inspection showed the thermostat failed to open and the pump impeller was corroded and worn, lowering circulation efficiency.

Replace the faulty parts and refill with qualified coolant. Run a full-load test, and the water temperature stays within the normal range. Hidden risks also need attention, such as mixed coolant, scale-blocked pipes and slight cylinder head gasket leakage. Regular maintenance should not only be carried out after faults appear.

For dusty and outdoor heavy-duty scenarios, inspect the diesel forklift cooling system regularly and replace antifreeze on schedule to prevent irreversible damage to pistons and cylinder heads caused by high temperature. Contact us for a complete maintenance guide for free.