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What is a Water-Cooled Engine?

By Lori Kilchermann
Updated Jan 31, 2024
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A water-cooled engine uses liquid coolant and a radiator to provide the cooling action of the engine. The coolant consists of a 50 percent mixture of anti-freeze and water; it is forced through the engine by a water pump and makes its way through the water-cooled engine via the water jacket. Most water-cooled engine designs use a sand investment casting process that produces a hollow iron or aluminum engine block and cylinder head. The coolant flows through the hollow space and absorbs engine heat, thus allowing the engine to operate at a controlled temperature.

Not all engines share the water cooling design; some engines are air-cooled. In this application, large cooling fins are typically cast into engine components to wick heat up and out of the engine. The wind passing through the cooling fins reduces the amount of heat retained in the engine. This type of cooling is not as effective on hot humid days as the water-cooled engine design.

Even on a hot day, a radiator is able to cool engine coolant by blowing air past the cooling tubes with a cooling fan. When moving at highway speeds, the cooling fan is not required to maintain the water-cooled engine at a safe operating temperature. While called a water-cooled engine, most engines do not use only water to cool themselves. Special mixtures of chemicals and additives known as antifreeze, typically a blend of methyl-glycol alcohol, are used as well; antifreeze resists freezing at sub zero temperatures while also resisting boil-over at severe high temperatures.

Most manufacturers recommend a 50-50 blend of antifreeze and water to give the most protection to both the engine and the cooling system. Special lubricants in the antifreeze give lubrication to water pump seals and bearings. Antifreeze should be changed every few years in order to give the best performance and ultimate protection possible.

Any racing vehicle using a water-cooled engine is required to use only water in the cooling system. This is due to the slippery nature of antifreeze and the difficulty in cleaning it off of the racing surface in the event of an accident. Water is easily dried and will evaporate in short order when contact is made with the racing surface. Antifreeze, however, remains very slick and is difficult to absorb with common oil drying substances, such as oil dry and saw dust. Antifreeze from a water-cooled engine can also remain on a tire's surface for many laps, creating a hazardous condition for the driver as well as the drivers around the affected vehicle on the track.

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Discussion Comments

By Vincenzo — On Mar 20, 2014

Ever used a heater in an vehicle with an air cooled engine, such as the old Volkswagen Beetle? The lack of a water cooled system to draw heat from means those heaters are electric and warm up immediately.

By Markerrag — On Mar 19, 2014

What a lot of people don't realize is that the "water" in a water cooled engine is directly related to how the heater in a car works. The heater will blow cold air until the water in the radiator heats up and provides a source of heat. That's the reason people warm their cars up on those cold days -- until the engine has been running and heating up the antifreeze, it can be very uncomfortable to drive around with cold air blowing on you.

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