The humble oil filter may look like a simple metal canister, but it's actually surprisingly complex, not to mention vital to your engine's longevity.
Oil filter's purpose is to filter out any contaminants from the oil. Keeping the oil free of particles (including tiny carbon fragments, shards of metal, or dirt or grit that have found their way into the engine), prevents them from causing any damage to the bearings, and other moving components.
Without a filter the engine is likely to suffer from worn journals, and premature bearing failure.
Oil is pumped from the sump, via the oil pick-up, through the filter, and up to the top of the engine, where it lubricates the vital components on its way back to the sump.
There are two main types of filter: the 'screw-on/spin-on' type, and 'cartridge' filters.
Both function in the same way, but with the former you replace the entire canister, and with the later, you simply replace the cartridge, and leave the housing in place.
Screw-on oil filters
These filters feature a metal housing and a rubber gasket that provides an oil tight seal between the filter, and the engine. Oil is pumped from the sump and enters the filter.
It is then passed over filtration media via a series of small holes around the perimeter of the filter. The media is commonly pleated paper, occasionally a pleated synthetic material.
This media removes harmful deposits, and the 'clean' oil carries on its journey around the engine after exiting the centre of the filter (through the large threaded hole).
The filter features an anti-drain valve, which keeps oil within the filter even when the engine is shut off. This maintains the volume of oil in the engine, and prevents the engine running with little or no oil when it’s first turned on.
There is also a bypass valve that bypasses the filtration media to prevent oil starvation if the filter becomes clogged, or blocked, or the demand from the fuel pump exceeds the filter's capacity.
Canister oil filters
These were once prevalent but were replaced with screw-on filters as they were considered to be less messy, and easier to change.
But in recent years canister filters have become increasingly popular as they produce less waste, and are cheaper to produce.
The canister filter housing is generally made of plastic, and offers the same anti-drain, and bypass functions as a screw-on filter. The filter is usually accessed by a threaded cap on the housing, which is removed using a large socket.