How Does a Car's Cooling System Work?

Your engine's cooling system is engineered to dissipate some of the heat generated from the engine during operation, while maintaining an ideal operating temperature for best efficiency. If it isn't kept in top working condition, overheating, inefficiency, and winter freeze up can result. All can cause serious damage. Let's have a look at how the cooling system works, and offer some general maintenance tips right here, right now. Welcome to the Auto Zone DIY Garage. The cooling system regulates engine temperature by circulating a mixture of chemical coolant and water through the engine's water jackets and radiator. When the heater valve is open, the coolant circulates through the heater core as well. A pump moves the coolant at a predetermined rate through the engine, where the heat is transferred to the coolant. The coolant then passes through a hose into the radiator, which transfers heat to the atmosphere. The pump might be driven directly off the engine, or by means of an accessory belt. On the 2.3 liter four cylinder in this 2008 Ford Fusion, the water pump is mounted on the engine block and driven by the accessory belt. The cooling system prevents overheating, which can result in engine damage. But it also helps ensure that the engine is hot enough to be efficient. A simple mechanical device, the thermostat, is charged with keeping the coolant at optimum temperature. To enable quick engine warmup and efficient running, the thermostat remains closed and prevents coolant from circulating through the radiator until the engine has reached a specific temperature. A radiator cap, which might also be located on an expansion tank separate from the radiator, is engineered to maintain a certain amount of pressure, which helps prevent boil over. A relief valve in the cap vents pressure if it becomes excessive. Did you know? All engine coolant products are not the same. Using the wrong type can cause serious problems. The liquid that circulates through your engine is a mixture of water and coolant that prevents freezing and boil over. Coolant is commonly called antifreeze, and it is usually based on ethylene glycol. But the additives that help prevent corrosion and lubricate cooling system parts can differ. Conventional coolant is usually green or red in color. A variation that employs different additives and is meant to last longer is dyed orange. Because the type of coolant specified for vehicles can vary, it's important that you add only the right product when topping off the coolant or refilling the system. It's also critical that you not mix different types. Mixing coolants will cause the original coolant in the vehicle to default to the lesser of the two types combined. For example, if green coolant is mixed with a long life coolant, the benefits of the long life will be lost, and the newly mixed coolant takes on the properties of the green only. Your owners manual can tell you what kind of coolant should be used in your car. Or just ask the experts at Auto Zone. It's also important that you use the right proportion of water and coolant. Pure coolant doesn't provide as much protection against boil over as does the mixture. But if the proportion of coolant is too low, the mixture can freeze. When liquids freeze they expand, and frozen coolant can crack the engine block or cylinder head and destroy the radiator. A 50-50 mix generally provides protection down to negative 34 degrees Fahrenheit. You can check the level of freeze protection your coolant provides by measuring its specific gravity with this tool, which looks something like a small turkey baster. Available at Auto Zone, the tool can give you an approximate reading of your freeze protection. The number of balls floating in the coolant indicates the degree of protection. After making sure the engine is fully cooled down, we undo the coolant reservoir cap, or radiator cap, and insert the probe tube into the tank. Squeezing the bulb, we draw fluid into the tube to the indicated level. Testing the coolant in our Fusion cooling system shows that it will provide freeze protection to at least negative 34 degrees Fahrenheit. Finally, coolant protection doesn't last forever. An annual flush and refill is a good idea for cars with conventional green or red coolant. A flush and fill should be performed whenever the system has been compromised, either due to defective parts or maintenance that require the coolant system to be opened. Otherwise, manufacturer intervals should be followed as stated in the vehicle's owners manual. Orange coolant, which is sold under a couple of different trade names, is meant to have an extended life, and the flush and refill period can be extended to two years. Some car manufacturers specify a five year or 150,000 mile service interval for orange coolant. But there is some controversy regarding those recommendations, and some car owners claim that the long intervals have led to problems. We recommend a flush and refill every five years when using orange coolant, and every two years when using green or red coolant. A flush and fill should also be performed whenever the system has been compromised, either to defective parts or maintenance that require the coolant system to be opened. Otherwise manufacturer intervals should be followed as stated in the vehicle's owners manual. The flush and refill is not difficult, and Auto Zone offers a kit that comes complete with instructions. You'll also find a video in the Auto Zone library that describes the process. Remember too that radiator and heater hoses don't last forever. They become soft and subject to failure as the miles and years add up. Check them for signs of deterioration on a regular basis. You'll find a video in the Auto Zone library that will show you how. That completes our discussion of cooling system basics. We hope this information helps if you decide to do the job yourself. For more information about the cooling system or any other automotive service topic, be sure to talk to the experts at Auto Zone. Get in the zone, Auto Zone.


AutoZone Antifreeze/Coolant Universal Yellow CONCENTRATE *5 Year/150K Mile Protection* 1 Gallon
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PEAK Antifreeze/Coolant Universal PREMIXED *10 Year/300K Mile Protection* 1 Gallon
AutoZone Antifreeze/Coolant Universal PREMIXED Dex-Cool Compatible *5 Year/150K Mile Protection* 1 Gallon
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