Also known as liquid-cooled. Where water or antifreeze is used to create a liquid jacket around the engine's cylinders and heads to cool. Water-cooling reduces engine noise, eliminates engine hot spots and localized seizures, and allows a motorcycle to be tuned for higher output. The opposite of air-cooled, where air flowing over the engine cools the cylinders/engine while the motorcycle is in motion. Although liquid cooling is heavier (adding to the bike's overall weight) than air-cooling, liquid cooling can maintain peak power during hard use -- a situation in which air-cooled bikes could overheat and lose power. Most cars are liquid-cooled, the most notable exception being VW bugs and other VWs with the flat four engine.