An oil filter is a mechanical device that prevents dirt and unburned fuel from circulating in the engine. Cars, trucks, motorcycles, boats, aeroplanes and generators use oil filters to keep harmful contaminants out of their engine fluids. When an engine is running it generates harmful byproducts including carbon monoxide, ash, chemical toxins and moisture which can quickly destroy expensive internal engine parts. The oil filter keeps these byproducts from getting into the engine and prevents them from contaminating fresh engine oil.

An engine oil filter is a round, cylindrical or rectangular canister with a flat-bottomed centre tube that's threaded at the top. An end disc that's either fibre or metal is bonded to each end of the filter medium which creates a pleated surface area inside the filter. The oil passes into the filter media and through it while under pressure as the engine operates. The oil is then filtered by the filter and is forced back into the engine oil passages through the centre tube and tapping plate.

A filter is considered good if it's able to capture all the debris and contaminants in the engine oil while still allowing the oil to flow. This is called capacity and it's a major factor in determining which oil filter you choose. Most oil filters have a micron rating that lets you know how small or large the particles that the filter is capable of catching are. You can also find out how well a particular filter performs by looking at the micron size and capture efficiency percentages on its label.

There are two main types of oil filters; full-flow and spin-on. Full-flow filters have a filter element that's encased in a metal canister or a plastic canister. A steel screen covers the outside of the filter and helps to disperse the oil evenly through the filter. These filters are less complex to use and are more easily accessible for inspection without draining the engine.

Spin-on filters have a filter element that's attached to a metal mount which you screw into the centre mounting stud of the engine. They're more expensive to buy but they're easier to remove and replace. They have a smaller diameter than full-flow filters but are just as effective at catching harmful debris while allowing the oil to flow freely through the filter.

When choosing an oil filter you should consider the recommended oil change interval for your vehicle as well as the filtration capabilities of each option. You should also check that the oil filter you're buying is rated to last for your specific make and model of vehicle. It should also come with an anti-drainback valve and it shouldn't have too low of a micron size or capture efficiency rating. Lastly, always get an oil filter wrench to help you loosen and remove the filter from the engine. It'll save you time and effort and it's a great way to prevent oil dripping from your hands.