What is the oil in a car engine?

Oil is used as a lubricant between parts that would otherwise wear each other out due to friction. The pressurized oil creates a liquid cushion that prevents metal-to-metal contact .

Of equal importance, oil helps to cool extremely hot parts (the bottoms of pistons, for example) by absorbing heat before draining to the bottom of the engine. Many high-performance cars have external oil coolers, similar in principle to radiators, to get rid of this excessive heat.