Auto questions: how car cooling systems work

The cooling system is an important part of your automobile. Major points on the history and functionality.

The design of the automobile cooling system has not changed significantly in concept in over 75 years. Advances in materials and manufacturing techniques have made it more efficient and reliable but it is still the same basic design that cars of the 1930’s and earlier used. Although it is a low tech system compared to others on a modern car, the cooling system plays a vital role in the operation of the vehicle. A car can function if its antilock braking system fails but it cannot function without a cooling system.

There are 6 major components of the cooling system. The first is the radiator which is probably the one with which most people are familiar. The others are the water pump, the engine block, the hoses, the fan and the radiator cap. We’ll look at the function of each of these components in turn but first, what does the cooling system do?

The engine in your car functions by combining gasoline and air in the combustion chambers and setting it on fire. It burns at temperatures approaching 2000 degrees F and some of this heat energy is used to propel the car. The rest escapes, some through the exhaust pipe and some heats up the engine. If you’ve ever put your hand by the tail pipe of a running car, you know that the exhaust gasses coming out are hot. If you drive your car at 55 miles per hour for 30 minutes or so at night and then stop and open the hood, you will see that the exhaust manifold is glowing red hot. Without a means of removing this heat, the engine would burn itself up in just a few minutes. So it’s the cooling system to the rescue.

The engine of your car contains special passages through which water can flow to remove excess heat. These passages must allow maximum contact of the water with the combustion chambers but must not allow the water to mix with the lubricating oil or gasoline that is also in the engine. In other words, the passages must form a sealed system that keeps the water separate from other parts of the motor. I’m sure you’ve seen what happens when water is left on a surface to evaporate. It leaves behind white stains. Theses are substances that are dissolved in the water and they can be left behind in your engine too. When these substances coat the walls of the passages, they reduce the amount of heat that can be removed from the engine and can cause overheating. This is why we use anti-freeze in our cars year round. The antifreeze contains chemicals that prevent the formation of deposits on the passage walls and also deterioration of the metal and keep the cooling system operating at peak efficiency.

The radiator is a square or rectangular arrangement of copper or aluminum tubes surrounded by hundreds or thousands of thin metal fins. Copper and aluminum are both excellent at transmitting heat which is what the radiator is intended to do. Hot water enters at the top of the radiator and flows to the bottom. The water heats the tubes and fins. Cool air flows around the fins and tubes and heat is transferred from the tubes to the air. When the water reaches the bottom of the radiator, it is significantly cooler. Here again, the use of anti-freeze is important to keep the tubes from clogging or having deposits form on the walls.

The radiator is connected to the engine by a hose at the top and one at the bottom. Hot water from the engine flows into the radiator through the top hose is cooled as we explained above and flows back into the engine through the bottom hose. Failure of the hoses is responsible for more roadside strandings than any other component on the car. They should be inspected every year and replaced every four to five years. Overheating caused by cooling system failures is more than an annoyance. Modern engines can be severely damaged and require expensive repairs.

Under its own power, water would not flow from the engine to radiator and back. Causing this movement is the job of the water pump. The water pump is mounted on the front of the engine and is driven by the engine through the fan belt. Water is pumped out of the engine and into the top of the radiator from where gravity causes it to flow back into the engine.

When a car is first started on a cold day, it is desirable to have the engine reach normal operating temperature as quickly as possible. This can be accomplished by restricting the flow of cooling water until the engine heats up. The thermostat is the device that is responsible for this. It is essentially a temperature operated valve that closes at low temperatures and opens at high ones. The thermostat is usually located at the top of the engine where the top radiator hose connects. When the engine starts, the thermostat is closed which causes the water in the engine to heat up rapidly. When the water reaches the right temperature, the thermostat opens and water begins flowing to the radiator where it can be cooled. If the thermostat sticks shut, the engine can overheat. If it sticks open, the engine may take a long time to reach proper operating temperature.

The radiator cap is located at the top of the radiator and is basically a pressure operated valve. As water heats up, its pressure increases. Some increase is desirable since it causes the water to move faster which increase cooling. Too much pressure however can cause radiators or hoses to burst. The radiator cap releases water when the pressure becomes excessive to prevent such problems. Some caps also work in reverse allowing water to reenter the radiator when the pressure drops.

The last component is the radiator fan. When the car is not moving, the fan forces air through the radiator to cool the water. Some fans are mounted on the water pump and driven by the fan belt while others are electrically driven. Some are made to spin freely when the car is moving at high speeds while others always spin at the same speed.