Your car’s cooling system has the important job of regulating the temperature of the engine. Just as Goldilock's pronounced judgment on the bears’ porridge, the cooling system ensures that the engine is “not too hot, not too cold, but just right”.
This is no fairy tale.
The engine burns fuel to generate power. Unfortunately, a car isn’t very efficient at turning chemical energy (fuel) into mechanical power. About 70% of the energy in fuel is converted to heat. Much of the heat escapes through the exhaust but some is absorbed by the engine.
The cooling system’s primary function is to transfer excess heat from the engine to the air. But the cooling system also allows the engine to quickly warm up to its optimal temperature (about 200 degrees Fahrenheit) and then keeps the engine running at a constant temperature.
How does it do that?
THE COOLING SYSTEM
The first law of thermodynamics says that heat passes in one direction only — from hot to cold. Your car’s cooling system illustrates this principle beautifully.
The pump sends fluid into the engine block, where it makes its way through passages around the cylinders. As fluid flows through the engine, it collects heat, which lowers the engine temperature.
The thermostat is located where fluid leaves the engine. At lower temperatures, the thermostat remains in the closed position, blocking the outlet to the radiator. Fluid goes back to the pump for recirculation through the engine.
As the fluid reaches temperatures of 180 to 195 F, the thermostat gradually opens, allowing fluid to flow through the radiator. By time the fluid is 200 to 215 F, the thermostat is completely open. Fluid leaves the engine and passes through the radiator.
The radiator acts as a heat exchanger. It’s located just inside the grill at the front of the car. Fresh air is forced through small cells — called the core — of the radiator by the speed of your moving car and the cooling fan mounted behind the radiator. The radiator transfers heat from the fluid into the air, and the fluid (now at a lower temperature) returns to the pump to begin another journey through the engine block.
Your car operates within a wide range of temperatures. To cool the engine, a fluid must have a low freezing point and a high boiling point, and be able to hold a lot of heat.
Water is very effective at holding heat but it freezes at too high of a temperature for a car engine. A solution of water and ethylene glycol, also known as anti-freeze, is the liquid coolant used in most cars. The addition of ethylene glycol significantly improves freezing and boiling points.
For example, pure water freezes at 32 F, while a 50/50 solution of ethylene glycol and water freezes at -35 F. The boiling point for pure water is 212 F, while the boiling point for the 50/50 solution is 223 F.
Coolant offers an operating range for heat transfer that’s expanded on both ends of the temperature scale. The cooling system is less likely to freeze, reducing the risk of damage to engine components. In addition, it’s more capable of dissipating excess heat.
Lastly, coolant contains rust inhibitors that help to keep the pump, thermostat and radiator in good working condition.
Caring for your auto cooling system isn’t difficult or costly. Preventive maintenance is a small investment that pays big dividends — miles of trouble-free driving and a longer life for your car. Here are a few tips.
- Check the condition of the coolant every time the oil is changed in your car. Use a hydrometer to measure the specific gravity.
- Keep the coolant filled to the proper level.
- Replace the coolant every two years or sooner, if necessary.
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