What is Oil Filter Working Principle?

The oil filter working principle depends on the gravitational force for filtration and supply of oil to the engine parts. I will discuss the oil filter types and working process in this article.

Oil filter working principle.

Oil Filter Working Principle

An oil filter is used in most motor vehicles’ lubrication systems to filter out the dirt or grit particles from the oil. It is an essential component in an IC engine that keeps the engine oil clean and helps it to get rid of many dirt particles.
So how the oil filter works? The main reason to install the oil is to save the engine from any dirt particles. When the engine is running there are many of dirt and debris that come from the atmosphere or any other sources. Firstly, it goes to the inlet port of the oil filter.
As the dirty oil or the new fresh oil comes to the inlet port of the engine oil, the material of the oil filter sucks the oil into it. The oil filter is typically made up of a porous material called filter media. This media can be made from a variety of materials, such as cellulose, synthetic fibers, or a combination of both. The filter media has tiny pores that allow oil to pass through while capturing and trapping contaminants.
After passing through the filter material the contaminants in the oil are sucked by the filter and the filtered oil is forced out to the outlet port. In many Air filters, there are anti-drawback valves to drain out the oil from the filter when the engine is off. These valves are operated by the ECU in the engine.
Depending upon the engine safety or the working principle of the oil filter, the oil filtration system is of two types- 
  1. By-pass system oil filter.
  2. Full-flow system oil filter.

By-Pass System Oil Filter

By-Pass system oil filter.


In the by-pass system, the whole oil does not pass through the filter at the same time, but some of the oil without being filtered goes to the bearing. The remaining oil passes through the filter and then goes to the bearings. When the engine is running continuously, for a long period, the whole oil is somehow filtered.
How does it work- As you can see on the diagram the by-pass flow system has a separate line to direct the engine oil to the various parts of the engine. The oil is stored in the oil pan and then the oil pump sucked and pressurized the oil. 
The pressurized oil then goes to the main oil line with constant pressure. The main oil flow line has a division of a bypass circuit, where the filter is actually situated. The oil is then filtered on the by-pass filter on the by-pass line and then goes to the engine moving parts and the bearings.
Some of the unfiltered oil directly goes to the engine systems through the main oil flow line. The continuous flow of the lubrication helps the engine to run smoothly in this system. 
[Note – In the by-pass lubrication system the unfiltered oil goes directly to the bearings and the moving parts, causing damage to the engine parts. So this system is no more available in the automobile sector.]

Full-Flow System Oil Filter

Full-Flow system oil filter.


The engine oil is stored in the oil sump. The oil sump is covered with all the dirt and the oil is also mixed with this dirt can cause engine damage. In the full flow system of the oil filter, the whole oil passes through the filter and then goes to the bearings. If the filter is clogged due to any reason, the system fails completely and bearings would be starved. 
How does it work – As per the diagram, the oil is kept in a separate space in an oil sump. The oil pump sucks the oil from the oil sump through the oil strainer. The oil strainer strains the bigger particles of dirt and sends them to the oil pump.
Then the oil pump pressurizes the oil into it and sends it to the full flow filter. Here the only way to get to the oil filter where the oil filters the dirt particles. The filter relive valve is situated on the top of the oil filter. The filter relive valve allows and disallows the oil to go through the engine parts. If there is sufficient oil and no need f extra oil then this valve will be closed, or when the engine is in the off position on that case this valve will remain closed. The filter relive valve is there to maintain the constant pressure of the oil flow to the engine. 
In this system, the oil filter plays a great role. If the oil filter gets clogged then the full system will fall down. Because the oil filter is the only way to send the pure oil to the moving bearings. 
[Note This system is now used in various engines for better performance and reliability.]


Lubricating oil is used in the engine to reduce friction. If the oil has dirt particles then the moving parts of the bearing will get clogged or wear and tear will happen. To increase the lifespan of the bearings and the engine parts the oil filter was introduced. 
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