How the Oil Filter Works

Written by tyler lacoma
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How the Oil Filter Works
A replacement filter, courtesy wikimedia commons

Oil is one of the key components in any engine, especially car engines. While most people assume that oil acts as a lubricant that keeps the parts of the engine moving easily without causing too much wear, oil also assumes several other jobs when the engine is working. It helps transfer heat into proper locations, seals the pistons and cylinders to prevent other fluids from escaping, and helps absorb both soot produced from combustion and outside particles that enter the engine.

However, oil is a fluid as well, and the contaminants that it absorbs can build up and cause problems. Too many contaminants in the oil can impede its lubricant properties, cause damage to pistons, and even create blockages within the engine. When cars were first created, the oil itself was replaced regularly, and filters were not really needed to maintain pure oil. Eventually, better cars and better oil were created, and oil filters became necessary to filter out the particles that built up in the oil. The filters themselves need to be replaced, but today's filters can last as long as 10,000 miles in the average car.

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Filter Structure

The filter is a metal can with the filtering element contained inside. This can is connected to the oil pump, which channels oil directly into the filter through a series of small holes. The filtering element is usually located around the sides of the can, while a central pipe pumps cleaned oil from the bottom of the filter into the engine again. There are often two different kinds of elements involved, a primary filter that removes larger particles and a secondary filter than can remove particles as small as 5 microns across.

A replacement filter, courtesy wikimedia commons
A replacement filter, courtesy wikimedia commons

Filtering Process

The difficulty with incorporating two different filters is that the second, smaller filter slows down the flow of oil significantly. Generally there are flow controls put into place within the filter that allow only a small amount of oil into the second phase, so the oil is not slowed down too much. Another problem is build-up within the filter itself: a filter used for a long time will eventually be caked with the particles it has cleaned from the oil, causing the oil to move slower and slower. Sometimes the filter reaches a stage where the oil cannot penetrate it at all, but simply sinks to the bottom. In these cases an emergency bypass valve is activated that drains the oil into the engine, but without it being filtered at all. It is important that filters be replaced before they reach this stage.

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