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The water may be used directly to cool the engine, but often has sediment, which can clog coolant passages, or chemicals, such as salt which can chemically damage the engine. Thus, engine coolant may be run through a heat exchanger that is cooled by the body of water.
A calibrated pressure-relief valve is usually incorporated in the radiator's fill cap. This pressure varies between models, but typically ranges from 4 to 30 psi (30 to 200 kPa). [4] As the coolant system pressure increases with a rise in temperature, it will reach the point where the pressure relief valve allows excess pressure to escape.
Water is inexpensive, non-toxic, and available over most of the earth's surface.Liquid cooling offers higher thermal conductivity than air cooling. Water has unusually high specific heat capacity among commonly available liquids at room temperature and atmospheric pressure allowing efficient heat transfer over distance with low rates of mass transfer.
As the boiling point of water increases with increasing pressure, these pressurised systems could run at a higher temperature without boiling. This increased both the working temperature of the engine, thus its efficiency, and also the heat capacity of the coolant by volume, allowing smaller cooling systems that required less pump power. [6]
Water-cooled engines contain passages in the engine block where cooling fluid circulates (the water jacket). Some small engines are air-cooled, and instead of having a water jacket the cylinder block has fins protruding away from it to cool the engine by directly transferring heat to the air.
In most familiar engines today, this water is circulated from the hot parts of the engine to a radiator, where it gives up its heat to the air. In early and low powered engines with hopper cooling there is little circulation. Water is instead slowly boiled off, with the heat of vaporisation needed to boil the water coming from the engine heat ...
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Proper engine coolant and a pressurized coolant system obviate these shortcomings of water. With proper antifreeze, a wide temperature range can be tolerated by the engine coolant, such as −34 °F (−37 °C) to +265 °F (129 °C) for 50% (by volume) propylene glycol diluted with distilled water and a 15 psi pressurized coolant system. Early ...