Bypass and Full-flow
Early automobile engines did not use oil filters. For this reason, along with the generally low quality of oil available, very frequent oil changes were required. The first oil filters were simple, generally consisting of a screen placed at the oil pump intake. In 1923, American inventors Ernest Sweetland and George H. Greenhalgh devised an automotive oil filter and called it the Purolator, a portmanteau of "pure oil later". This was a bypass filter: most of the oil flowed directly from the oil pan to the engine's working parts, and a smaller proportion of the oil was sent through the filter via a second flow path in parallel with the first. The oil was thus filtered over time. Modern bypass oil filter systems for diesel engines are becoming popular in consumer applications, but have been in commercial use for some time due to potential reduction in maintenance costs. Oil filters are generally located near the middle or bottom of the engine.
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