Car engines are made of metal parts that constantly rub against each other. If left alone, that rubbing motion creates friction, which heats up the engine, eventually to the point that the engine no longer works. To solve - or at least delay - the problem, the engine is filled with a lubricant: oil. The oil doesn't adhere to the metal parts, so friction is reduced. However, over time, tiny bits of metal join with dirt that seeps into the engine, resulting in dirty oil.
Oil filters help clean the oil. The filter can clog up with dirt and become less efficient until it eventually has to be replaced. Traditional filters don't completely clean the oil, and eventually there must be an oil change.
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