Even though modern-day vehicle engines have improved a lot, they’re still not efficient in transforming chemical energy into mechanical power. Most of the energy from your Nissan’s engine is converted into heat, which is why it has a cooling system. The cooling system plays a crucial role in Nissan’s performance – it prevents the engine from overheating by transferring heat to the air. Ideally, the engine should operate at a fairly high temperature, otherwise, the components will wear out faster than intended, it will emit more pollution and it will be less efficient. That being said, the cooling system allows the engine to heat up as fast as possible, and then to regulate the engine’s temperature at a constant.
There are two basic types of cooling systems – liquid- and air-cooled systems. Liquid cooling systems feature a fluid that circulates through the passageways and pipes of the engine. As the fluid passes through the engine, it absorbs heat before leaving the engine and going through a radiator, where the heat in the fluid is blown into the air through an exchanger. Nissan radiators play a crucial role in the cooling of the engine, but I’ll talk more about them later. Air-cooled systems are found on older Nissans. These systems feature aluminium fins around the engine block, and they transfer heat away from the cylinders. A powerful fan forces the air over the fins, cooling the engine in the process.
Nissan’s cooling system has a lot of plumbing. There’s a pump that sends fluid into the engine block, where it passes through the passages around the cylinders. Next, the fluid returns through the cylinder head and reaches the thermostat. If the thermostat is closed, the fluid goes back to the pump. If open, the fluid will go through the radiator before going back to the pump. The cooling system also features a separate circuit for the heating system, which takes the liquid from the cylinder head and takes it through the heater core before sending it back to the pump.
The fluid used to cool the engine has a high boiling point, low freezing point, and it has the ability to hold a lot of heat. Water is one of the most effective liquids for the job, except it freezes at too high of a temperature to be used in engines. For that reason, most vehicles use a mix of water and ethylene glycol, commonly known as antifreeze. The temperature of coolants can sometimes reach up to 135 degrees Celsius, and even with ethylene glycol in the mix, these temperatures can boil the coolant, which is why cooling systems use pressure to raise the boiling point even further. Most vehicles have a pressure limit of 15PSI, raising the boiling point for an extra 25 degrees.
Then there’s the pump, which is driven by a belt connected to the crankshaft of your Nissan’s engine. The pump circulates the fluid whenever the engine is operating by using centrifugal force. It sends the fluid to the outside while it spins, causing it to be drawn from the centre continuously. The inlet of the pump is near the centre so that the returning fluid from the radiator hits its vanes. The vanes fling the liquid to the outside, where it enters the engine, going through the cylinder head and engine block, then the radiator, before going back to the pump.
The radiator is designed to transfer the heat that comes with the coolant into air blown through it by the fan. Most Nissan radiators are made of aluminium, and the coolant flows from the inlet to the outlet through tubes mounted parallelly. The fins conduct the heat and transfer it to the air that flows through the radiator. Sometimes, the tubes may have a fin inserted into them which is known as a turbulator, increasing the turbulence of the fluid so that it can be cooled more efficiently. The amount of heat that’s transferred from the liquid to the tubes depends on the difference in temperature between them.
Lastly, there’s a pressure cap that increases the boiling point of the coolant, as aforementioned. It does so in a similar manner to pressure cookers. The cap is a pressure release valve with 15 PSI, allowing the boiling point of water to increase when placed under pressure. When the liquid in the cooling system heats up, it expands, resulting in pressure build-up. The cap is the only place where the pressure can leave the system. If the pressure reaches 15 PSI, the pressure cap opens, allowing coolant to leave the cooling system. The coolant flows via the overflow tube into the overflow tank, helping keep air out of the cooling system. When the temperatures drop, a vacuum is created that pulls open another spring-loaded valve, taking water back from the overflow tank.