What details cause the engine to overheat?

Summer arrives, truck engines often tend to experience high temperature phenomena, which is caused by engine overheating. Engine overheating refers to the engine temperature exceeding the maximum working temperature range (80-90°C), and sometimes you can even see the radiator boiling.

The main causes and troubleshooting methods are mainly:

1. Insufficient coolant.

The coolant is the carrier of the heat in the cooling circulation system. The heat inside the engine is dissipated by the water. If the coolant in the cooling system is reduced due to leakage or evaporation, the heat dissipation will naturally be reduced, causing the engine to accumulate excessive heat, resulting in engine overheating.

Diagnosis and troubleshooting methods: Check if the external part of the cooling system is leaking. If there is a water leak, it indicates that the engine overheating is caused by the leak, and the leak should be promptly eliminated.

If there is no water leak, you can open the radiator cap and observe the sufficiency of the coolant. If the coolant is severely insufficient, it is mostly due to the lack of coolant replenishment for a long time, which has led to engine overheating. In this case, the coolant should be replenished.

2. The fan belt is too loose and slippery.

The size of the cooling intensity of the cooling system depends on the fan speed, if the fan drive belt is too loose and slippery, will cause a decline in the efficiency of power transmission, which not only makes the fan speed down, cooling intensity is reduced, at the same time the water pump speed is also down, the displacement is reduced, so that the cooling water flow rate is slow, the heat can not be quickly taken away, resulting in poor heat dissipation.

Diagnosis and Troubleshooting Method: When the engine is not running, manually rotate the fan blades. If the fan can be easily rotated, it indicates that the fan belt is too loose, which is causing poor cooling. The belt should be adjusted accordingly. Adjust the belt tensioning device, such as the alternator or a dedicated tensioner pulley, to increase the belt's pretension. The inspection standard is to press down on the belt with a force of 29-49N (3-5kg) between the alternator and the fan pulley, resulting in a deflection of 10-20mm.

3. Thermostat Malfunction.

The thermostat is located at the engine's water outlet and its function is to regulate cooling intensity. When the engine temperature is low, it cuts off the main circulation route and connects the smaller circulation route to reduce heat dissipation, allowing the engine temperature to rise quickly. When the engine temperature rises to the specified level, the thermostat connects the main circulation route and closes the smaller circulation route.

If the thermostat is damaged and cannot connect the main circulation route, it causes poor coolant circulation. As a result, the heat absorbed by the coolant cannot be transferred to the radiator for dissipation, leading to engine overheating.

Inspection and Troubleshooting Method: Remove the thermostat and place it in hot water. When the temperature reaches around 70°C, the main valve should start to open. It should be fully open at 80-86°C, with a valve lift generally not less than 9mm. If it does not meet these requirements, the thermostat should be repaired or replaced.

4. Excessive Scale in the Cooling System.

Engines that have been in use for a long time are prone to excessive scaling in the engine block and radiator, leading to poor heat dissipation.

Method of Elimination: Perform chemical cleaning on the engine block and radiator. Commonly used chemical cleaning solutions include 8% caustic soda solution, 10% sodium carbonate solution, and 2.5% hydrochloric acid solution. When using the first two solutions, the solution should be retained in the cooling system for 10-12 hours; when using the third solution, the engine should be started immediately after injection and run at low idle without load for 1 hour. During the cleaning process, the thermostat should be removed. After draining the cleaning solution, remove all drain plugs to clear out dirt, then flush the engine's water jacket and radiator with clean water using the reverse flow method until the water runs completely clean. During flushing, the water pressure should be controlled within 30 kPa.

5. Delayed Fuel Injection Timing.

If the fuel injection advance angle is too small, a significant portion of the combustion process occurs during the expansion stroke. This increases the volume above the piston and the contact area between the flame and the cylinder wall, leading to increased heat absorption. As a result, thermal efficiency decreases, exhaust temperature rises, and more heat is transferred to the coolant, causing the engine to overheat.

Diagnosis and Troubleshooting Method: If the engine lacks power, produces a muffled noise, has high coolant temperature, and the exhaust pipe temperature is abnormally high, it indicates that the engine overheating is mostly due to a small fuel injection advance angle. The injection timing should be adjusted according to the method described in the diesel fuel supply system.