What’s in an oil filter, and how does it work? (Pt. 2)

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An oil filter attached to an engine.

A screw-on oil filter in its natural habitat, attached to an engine. (Photo Credit: CC BY-SA/Dvortygirl/Wikipedia)

The components of an oil filter work to remove impurities and cycle cleaned oil back into the engine, for maximum engine efficiency. CLICK HERE if you missed the beginning of this article.

What’s in an oil filter?

You’ve been very patient, so here you are. These are the key components of an oil filter:

Oil filter parts – Tapping plate

Oil enters and exits the filter through the tapping plate. Small holes around the edge of the plate allow for free flow of oil into the container. The center hole in the plate allows filtered motor oil back out, and allows for the attachment of the oil filter to the engine block.

Oil filter parts – Anti-drainback valve

This is a rubber valve with a flap that prevents oil from draining back into the filter when the engine is shut off. Why do the job a second time when the oil in question is already cleaned?

Oil filter parts – Filter medium

A porous membrane of cellulose and synthetic fibers of glass and polyester, this part of the oil filter is resin-saturated in order to make the filtering process more efficient.

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Oil filter parts – Pleating

Depending upon the thickness of the filter medium, there are more or less pleats. Pleating allows for greater surface area of the membrane within the oil filter, which in turn translates to enhanced filtering power.

Oil filter parts – Center steel tube

This works as both a mounting implement and a pathway through which oil is returned to the engine.

Oil filter parts – Relief valve

If pressure builds enough to force the calibrated spring within the oil filter downward, the relief valve opens, sending unfiltered oil into the center tube through the top. This ultimately occurs at cold startup, if the oil is too thick to filter.

Oil filter parts – End disc

Unfiltered oil shouldn’t leak into the center tube. Thus, the fiber or metal end disc is attached to each end of the filter. Some oil filter brands use a form of sealant to achieve this same end without the end disc.

Oil filter parts – Retainer

This thin piece of metal is a kind of leaf spring, keeping the filter medium and end disc pushed tight against the tapping plate.


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