Diesel Generator Cooling Water Temperature Management

In industrial production, construction projects, emergency power supply, and many other fields, diesel generator sets play an indispensable role. They provide stable power support for various equipment and systems, ensuring smooth operations. However, in order for diesel generator sets to run efficiently, stably, and for long periods, the management of coolant temperature is of vital importance. This article will explore in depth the knowledge related to diesel generator cooling water temperature, including its importance, influencing factors, common misconceptions, and correct management methods, to help you better maintain and use generator sets.

During operation, the combustion chamber of a diesel generator engine produces a large amount of heat. If this heat cannot be released in time, it will cause the engine to overheat, which may then trigger a series of serious problems, such as engine component damage, power reduction, and increased fuel consumption. The main role of the coolant is to absorb and dissipate this heat, maintaining the engine within a suitable temperature range for operation.

Generally speaking, the coolant temperature of a diesel generator set should be controlled between 80°C and 95°C. Within this range, the engine's combustion efficiency is highest, component wear is minimal, and good lubrication is ensured. If the coolant temperature is too high, the engine overheats, causing thermal expansion of components, disrupting the normal fit clearance between parts, increasing wear, and potentially leading to severe accidents such as cylinder scuffing or bearing seizure. If the coolant temperature is too low, the engine cannot fully burn fuel, resulting in incomplete combustion. This not only reduces the generator set's output power but also causes poor fuel atomization, extended afterburning, and other issues, accelerating component damage, reducing performance and economy. Furthermore, water vapor from combustion may condense on the cylinder wall, causing metal corrosion, while unburned diesel dilutes the lubricating oil, affecting lubrication and even leading to piston ring seizure or valve sticking, which further reduces engine performance and lifespan.

The stability of diesel generator coolant temperature is crucial to its normal operation. Multiple factors may cause abnormal coolant temperature, mainly relating to the performance of cooling system components, the condition of the coolant itself, and other external conditions. The following will detail these factors and their specific effects on coolant temperature.

Thermostat: The thermostat is an important part of the cooling system. Installed in the engine combustion chamber, its main function is to control the combustion chamber temperature. When the engine temperature is below the specified value (e.g., 82°C), the thermostat closes, and the coolant circulates within the engine in a small loop, allowing the engine to warm up quickly. When the engine temperature reaches the specified value, the thermostat fully opens, and the coolant circulates in a large loop, releasing heat through the radiator. If the thermostat malfunctions and cannot fully open at the specified temperature, coolant circulation will be disrupted, potentially causing the engine temperature to be too high or too low. For example, without a thermostat, coolant cannot maintain circulating temperature, which may trigger low-temperature alarms.

Cooling Fan and Radiator Fins: The cooling fan accelerates air flow around the radiator, helping it to dissipate heat. If the fan fails—due to motor damage, blade deformation, or looseness—it cannot operate properly, reducing cooling efficiency and raising coolant temperature. The radiator fins are the main heat-dissipating component for coolant. If their surfaces are clogged with dust or debris, or if rust or leaks occur, cooling performance is impaired. For example, clogged fins prevent coolant temperature from dropping, while rusted fins may cause leakage, leading to poor coolant circulation.

Water Pump: The water pump drives coolant circulation throughout the system. If the water pump fails—such as through worn drive shafts or damaged impellers—it cannot operate properly, blocking coolant flow and raising engine temperature. Therefore, it is necessary to regularly check the water pump's operating condition to ensure proper functioning.

Expansion Tank and Valves: The expansion tank compensates for coolant expansion and contraction, keeping pressure stable within the cooling system. The intake and exhaust valves on the expansion tank are also very important, as they regulate system pressure. If the intake or exhaust valves are damaged, coolant circulation will be directly affected. For example, the intake pressure should be 10 kPa and the exhaust pressure 40 kPa; if these values do not meet specifications, coolant circulation may be hindered, reducing heat dissipation.

Coolant Level Too Low or Not Meeting Specifications: A coolant level that is too low will directly raise coolant temperature, as circulation cannot proceed normally. The composition and ratio of coolant are also very important; the specified mixture is 50% antifreeze + 50% softened water + DCA4. If coolant does not meet specifications, it may cause pipe blockages or rust inside walls, hindering circulation. For example, using non-compliant coolant may cause freezing at low temperatures—damaging system parts—or bubbles at high temperatures, reducing cooling efficiency.

Air Mixed in Coolant: If air enters the diesel generator cooling system, pipelines will not be smooth, and coolant circulation will be disrupted. Air forms bubbles in the coolant, obstructing flow and reducing cooling performance. Therefore, when adding coolant, it is necessary to ensure no air remains in the system, which can be done through exhaust procedures.

Engine Load: When the engine operates under high load for extended periods, it generates large amounts of heat, and the cooling system may not dissipate it in time, causing coolant temperature to rise. Thus, generator load should be reasonably arranged to avoid prolonged high-load operation.

Ambient Temperature: If the working environment temperature is too high, cooling performance is reduced, causing coolant temperature to rise. For example, in hot summer or poorly ventilated areas, coolant temperature rises more easily. Conversely, in cold winter environments, coolant warms up more slowly, and measures must be taken to ensure it reaches the appropriate range.

In practice, some operators hold misconceptions about diesel generator coolant temperature. For instance, some believe that the lower the coolant temperature, the better. They think that at lower temperatures, cavitation will not occur in the water pump, circulation will not be interrupted, and there is a safety margin during use. However, this view is incorrect. In fact, as long as the coolant temperature does not exceed 95°C, cavitation will not occur, and circulation will not be interrupted. On the contrary, if coolant temperature is too low, the harm to the diesel engine is significant.

As oil viscosity in the lubrication system increases, part friction resistance rises, leading to poor lubrication and increased wear. For example, when coolant temperature is 30°C, wear on cylinder liners, pistons, and piston rings is about five times greater compared to 80–90°C. Low coolant temperature also worsens combustion, causing poor fuel atomization, extended afterburning, and rough operation, which accelerates damage to crankshaft bearings, piston rings, and other parts, reducing performance and economy. Water vapor from combustion condenses on the cylinder wall, causing metal corrosion. Unburned diesel dilutes oil, worsening lubrication. Incomplete combustion produces deposits that cause piston rings to stick in grooves and valves to seize, lowering cylinder pressure at the end of compression. As heat loss increases, engine power drops and fuel consumption rises. For example, at 40°C coolant temperature, fuel consumption is about 10% higher than at 80°C.

Therefore, diesel engine coolant temperature is not "the lower the better." Generally, it is most suitable to maintain it between 80–95°C.

The temperature differences between seasons are significant, and the requirements for diesel generator coolant temperature also vary.

In summer, ambient temperatures are higher, and in some regions, they may even reach 44.5°C. In such high-temperature environments, the coolant temperature of diesel generator sets rises quickly. When the water temperature of a diesel engine reaches 100°C, it can easily cause cylinder scuffing accidents. Therefore, when the coolant temperature of a diesel generator set exceeds about 95°C, it should be shut down or its load reduced. In summer, special attention should be paid to the maintenance of the cooling system, ensuring that components such as cooling fans and radiator fins function properly, while maintaining good ventilation conditions. At the same time, the coolant level and quality should be regularly checked, and coolant should be replenished or replaced in time. If conditions permit, auxiliary cooling devices can be installed in the system—such as enlarging the radiator's heat dissipation area or installing additional cooling fans, to enhance the cooling effect.

In winter, ambient temperatures are low, and so is the operating temperature of diesel generator sets, resulting in lower coolant temperatures. Consequently, the coolant warms up more slowly. When the diesel engine delivers effective power, the coolant temperature should be around 80°C. During winter operation of diesel generator sets, when preparing to supply power under load, it is best to ensure that the coolant temperature is around 80°C. To maintain the coolant within a suitable range, the following measures can be taken:

Use antifreeze to prevent the coolant from freezing at low temperatures.

Preheat the coolant using heating equipment so that it reaches around 80°C before starting the generator set.

Insulate the generator set, for example by installing thermal insulation covers around it, to reduce heat loss.

Appropriately adjust the cooling system's heat dissipation, for example, by closing part of the radiator shutters to reduce the dissipation area, so that the coolant temperature can quickly rise to the proper range.

Coolant temperature is a critical factor affecting the efficiency and service life of diesel generator sets. Both excessively high and excessively low temperatures negatively impact generator operation. Therefore, coolant temperature should be controlled between 80°C and 95°C.

We have also analyzed the various factors that influence coolant temperature, including failures of cooling system components, coolant issues, engine load, and ambient temperature, and we have proposed corresponding management methods—such as regularly inspecting cooling system components, keeping coolant sufficient and compliant, reasonably controlling engine load, maintaining good working environments, and adjusting coolant management according to seasonal changes.

Only through scientific and rational management and maintenance can the coolant temperature of diesel generator sets remain within the normal range, ensuring reliable operation, improving efficiency, and extending service life, thereby providing dependable power support for our production and daily life.