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Internal combustion engine cooling
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<p>Internal combustion engine cooling uses either air or liquid to remove the <a href="/facts/Waste_heat/nGBH1Vc8">waste heat</a> from an <a href="/facts/Internal_combustion_engine/Ju4BXzj0">internal combustion engine</a>. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. <a href="/facts/Watercraft/XX8YawP1">Watercraft</a> can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a <a href="/facts/Radiator/W592jFf2">radiator</a>. </p><p>Water has a higher <a href="/facts/Heat_capacity/I63nzSyp">heat capacity</a> than air, and can thus move heat more quickly away from the engine, but a radiator and pumping system add weight, complexity, and cost. Higher power engines can move more weight but can also generate more waste heat, meaning they are generally water-cooled. <a href="/facts/Radial_engine/tS0ljlb7">Radial engines</a> allow air to flow around each cylinder directly, giving them an advantage for air cooling over <a href="/facts/Straight_engine/T1537bJF">straight engines</a>, <a href="/facts/Flat_engine/MMHDYBzH">flat engines</a>, and <a href="/facts/V_engine/nNIeYP6c">V engines</a>. <a href="/facts/Rotary_engine/QkxnRk0x">Rotary engines</a> have a similar configuration, but the cylinders also continually rotate, creating an air flow even when the vehicle is stationary. </p><p>Aircraft design more strongly favors lower weight and air-cooled designs. Rotary engines were popular on aircraft until the end of <a href="/facts/World_War_I/vITTUanQ">World War I</a>, but had serious stability and efficiency problems. Radial engines were popular until the end of <a href="/facts/World_War_II/2efV5L1U">World War II</a>, until <a href="/facts/Gas_turbine/JJJNwXrG">gas turbine</a> engines largely replaced them. Modern propeller-driven aircraft with internal-combustion engines are still largely air-cooled. Modern cars generally favor power over weight, and typically have water-cooled engines. Modern motorcycles are lighter than cars and both cooling methods are common. Some sport motorcycles are cooled with both air and oil that is <a href="/facts/Suzuki_Advanced_Cooling_System/hy4y1Lat">sprayed underneath the piston heads</a>. </p>