Basic Knowledge About Engine

1. What are the causes of excessively high cylinder coolant temperature?

Answer: The following are possible causes of excessively high coolant temperature in individual cylinders:

1). Overload or severe afterburning in that cylinder.

2). Piston overheating or cylinder seizure.

3). Coolant shut-off valve closed or damaged, causing coolant cut-off.

4). Blockage in the coolant pipe leading to that cylinder.

The following are possible causes of generally excessively high coolant temperature in all cylinders:

①. Diesel engine overload.

②. Insufficient freshwater pressure and coolant flow.

③. Blockage in the freshwater cooler tube bundle or scale buildup on the cooling surfaces, resulting in poor cooling performance.

④. Insufficient seawater pressure and flow, or a clogged filter or bottom valve.

⑤. The main engine's freshwater heating element is not shut off or the steam valve is leaking, causing the circulating water temperature to rise. The freshwater temperature control valve may be malfunctioning, causing the cooler to bypass.

Overheating of diesel engine coolant often leads to excessively high cylinder liner temperatures. This can range from mild, affecting engine lubrication and accelerating wear, to severe, causing cylinder scoring, seizure, or component cracking. Therefore, coolant temperature should be closely monitored and strictly controlled.

2. What measures should be taken when cylinder overheating is caused by insufficient or interrupted coolant or cylinder oil supply?

A: When cylinder overheating is found to be caused by insufficient or interrupted coolant or cylinder oil supply, the following measures should be taken:

1）. Immediately switch to light diesel oil, reduce vehicle speed, check the temperature of each cylinder, cut off fuel supply to the overheating cylinder, and fill the cylinder with maximum cylinder oil.

2）. Check the coolant level in the affected cylinder. If the coolant level is insufficient or completely interrupted, gradually increase the coolant level unless the overheating reaches a dangerous level. If the overheating has reached a dangerous level, stop the engine immediately, crank the engine, and check the water pump and system. Do not immediately increase the coolant level to avoid excessive stress.

3）. If the coolant supply is normal, but cylinder overheating is caused by insufficient or interrupted cylinder oil supply, reduce speed and increase cylinder oil supply. If the situation is not serious, slowly restore the normal oil supply.

At this time, pay attention to:

①. The piston coolant supply should continue as normal to remove heat from the piston as much as possible and accelerate cylinder cooling.

②. After the cylinder overheating is eliminated, the oil pump for that cylinder can be resumed, and the vehicle speed can be gradually increased. Observe the engine for a period of time.

3. What are the reasons for unstable or insufficient piston cooling oil pressure?

Answer: The reasons for unstable or insufficient piston cooling oil pressure may include:

1）. Insufficient circulating oil.

2）. Leaking or blocked oil pressure regulating valve of the lubricating oil pump.

3）. Loose lubricating oil pipes, resulting in a large amount of lubricating oil loss inside the diesel engine (due to loose oil pipe connectors, loose expansion sleeves, or broken oil pipes).

4）. Air entering the lubricating oil pump.

5）. Lubricating oil temperature is too high, causing diesel fuel to mix into the lubricating oil, making its viscosity too low. If the pressure in the cooling oil system drops, the oil pressure regulating valve should be adjusted first. If the pressure still cannot be restored to the normal range, the diesel engine must be stopped for further inspection and troubleshooting.

If the piston cooling oil outlet temperature of a particular cylinder rises, the cause should be identified immediately and restored as soon as possible. If the cause cannot be found immediately, the load must be reduced and fuel injection to that cylinder must be stopped, operating at reduced cylinder capacity. Simultaneously, close monitoring of that cylinder's movement is necessary to prevent cylinder scoring or seizure.