A modern internal combustion engine is a complex mechanism with thousands of parts in constant motion and friction. To ensure their longevity, engineers have developed a lubrication system that not only reduces friction, but also dissipates heat and removes wear debris. However, the oil itself becomes contaminated over time, and this is where oil comes into play. oil filter - an invisible, but critical element, without which the life of the motor would be reduced significantly.
Many car owners perceive this part as a consumable item that is simply changed during scheduled maintenance, without thinking about the principles of its operation. In fact, a complex cleaning process takes place inside the metal cylinder, depending on the pressure, viscosity of the liquid and the quality of the filter element. Understanding that how does an oil filter work, will help you avoid fatal mistakes when choosing spare parts and servicing your car.
In this article, we'll take a closer look at the design of the unit, look at the different types of materials, and explain why saving on this component can lead to a major engine overhaul. You will learn about the hidden functions of valves and understand how often replacement is actually necessary in real-world operating conditions.
Main purpose and operating principle
The main task of any filter in the lubrication system is to trap solid particles formed as a result of wear of rubbing pairs and fuel combustion. When the engine is running, motor oil circulates through the channels, collecting microscopic metal shavings, carbon deposits and dust. If this abrasive remained in the system, it would act like sandpaper, rapidly destroying the crankshaft journals and cylinder surfaces.
The operating principle is based on passing liquid through a special porous material. Dirty oil under pressure is supplied by a pump from the oil pan and passes through the walls of the filter element. The cleaned liquid is directed to bearings and other components, and all dirt remains inside the housing. It is important to note that cleaning efficiency directly depends on the surface area and density of the material.
⚠️ Attention: Never start the engine if you accidentally forgot to remove the protective film from the O-ring of the new filter or did not fill it with oil before installation. A dry start can instantly damage the liners.
There is a common misconception that the filter only catches large debris. In fact, modern elements are capable of capturing particles up to 10-20 microns in size, which is comparable to the thickness of a human hair. It is precisely this fineness of cleaning that is necessary to protect hydraulic compensators and phase shifters in modern engines.
Design and key elements
Visually oil filter It is a metal glass with a threaded hole, but there is a hidden engineering system inside. The basis is a filter element made of special paper impregnated with resins for resistance to high temperatures and aggressive chemical environments. The paper is folded like an accordion, which allows you to increase the filtration area several times while maintaining the compact dimensions of the body.
However, the design is not limited to just paper. The critical element is bypass valve. In the cold season, when the oil thickens, or when the filter is heavily contaminated, the inlet pressure increases sharply. To prevent the engine from being left without lubrication, the valve opens and allows dirty oil to bypass the filter. This is the “lesser evil” to avoid oil starvation, but it emphasizes the importance of timely replacement.
Another important component is the check valve. It prevents oil from the filter and lines from draining back into the crankcase after the engine is stopped. Thanks to this, the next time the engine is started, the oil instantly reaches the rubbing parts, reducing wear during a cold start. Without this valve, the pump would have to re-prime the system, which would take several seconds to run dry.
What's inside the paper element?
The paper is folded into a multi-layered star or spiral. The number of folds and their depth directly affect the resource. Cheap filters have fewer folds, which speeds up their clogging and increases flow resistance.
Types of filter materials
When choosing a spare part, drivers often look only at the brand, ignoring the material from which the item is made. This parameter determines how long the filter will retain its properties and what degree of cleaning it will provide. There are three main types of materials on the market, each of which has its own application characteristics.
The most common option is cellulose. This is a natural fiber treated with chemical compounds. It traps about 90-95% of contaminants larger than 20 microns. Such filters are cheap to produce, but have a limited resource and are sensitive to overheating. They are not always suitable for normal urban conditions and synthetic oils with long drain intervals.
Synthetics are considered a more advanced solution. Artificial fibers make it possible to create materials with a more uniform pore structure. Synthetic filter is capable of retaining up to 99% of particles measuring 10 microns and withstands higher temperatures without destroying the structure. It is the ideal choice for modern turbocharged engines operating under extreme thermal conditions.
The third type is mixed materials, combining cellulose and synthetics. This is a compromise solution that allows you to get good filtering properties at a reasonable cost. In such elements, synthetic fibers often play the role of a frame or an additional barrier for fine dust, while the bulk of cellulose retains large fractions.
When buying a filter, knock on the body: a high-quality product sounds muffled and denser due to more folds of paper and thick walls. Cheap analogues often rattle because there is empty or little filler inside.
Full-flow and partial-flow systems
There are two main oil purification schemes used in the automotive industry, and understanding the difference between them is important to diagnosing problems. Most passenger cars are equipped with full-flow systems. In this scheme, the entire volume of oil supplied by the pump passes through the filter. This provides a high degree of purification, but creates a certain flow resistance.
In a full flow system, bypass valve reliability is critical. If the filter becomes completely clogged and the valve is stuck in the closed position, the engine will be left without lubrication. If the valve gets stuck open, the oil will become dirty. This is why build quality and valve opening pressure calibration are key parameters during production.
Partial flow systems are more often found on heavy equipment or in sports engines as an additional cleaning stage. In them, only part of the oil constantly circulates through a fine filter, while the main flow passes through the mains. This allows the use of filters with very fine porosity without fear of high resistance, but requires the installation of an additional pump or a complex channel system.
| Parameter | Full flow filter | Partial flow filter |
|---|---|---|
| Oil coverage | 100% volume | 10-20% volume |
| Resistance | High | Low |
| Cleaning fineness | Medium (20-40 microns) | High (up to 5 microns) |
| Application | Passenger cars, trucks | Special equipment, sports cars |
Signs of contamination and the need for replacement
It is difficult to determine the condition of the filter without disassembling the engine, but there are indirect signs indicating that the element’s resource has been exhausted. First of all, you should focus on the manufacturer’s regulations, but real operating conditions often make their own adjustments. If you often sit in traffic jams or drive on dusty roads, replacement intervals need to be shortened.
One of the symptoms of a clogged filter may be the oil pressure light coming on when the engine warms up. This occurs because the cold, viscous oil has difficulty passing through the clogged pores and the inlet pressure drops below a critical level, opening the bypass valve or signaling a problem. There may also be a loss of power and increased fuel consumption due to increased resistance in the lubrication system.
Don't wait for alarming symptoms to appear. Replacing the oil filter must be done strictly in conjunction with an oil change. An attempt to save money by leaving the old filter when filling in fresh oil leads to the fact that the new lubricant is instantly contaminated with wear products remaining in the old element and loses its properties.
☑️ Check before replacement
Consequences of driving with a clogged filter
Ignoring the need to replace the filter is a direct path to expensive repairs. When the element is completely clogged with dirt, the pressure in the system drops and the valves open, allowing unrefined oil to pass through. Abrasive particles begin to circulate throughout the engine, causing accelerated wear of the camshaft bearings and crankshaft journals.
In the long term, this leads to knocking, increased clearances and a drop in compression. The engine begins to “eat” oil, smoke and lose traction. It is often impossible to restore the geometry of worn parts; boring the blocks or completely replacing the engine is required. The cost of such repairs is not comparable to the price of a high-quality filter.
⚠️ Attention: Using filters from unknown brands with poor quality paper may cause it to tear. In this case, all accumulated debris will immediately fall into the oil channels, which is guaranteed to cause the engine to jam.
In addition to mechanical wear, contaminated oil oxidizes faster and loses its cleaning properties. Carbon deposits settle on the pistons and valves, disrupting heat dissipation. In diesel engines with diesel particulate filters (DPF), the use of unsuitable filters can lead to rapid failure of the vehicle's entire environmental system.
An oil filter is not just a mesh, but a valve that regulates cleanliness and pressure in the system. Its serviceability directly determines whether your engine will go 300 or 500 thousand kilometers without opening.
How to choose and replace the filter correctly
When purchasing a spare part, first of all pay attention to the catalog number corresponding to your engine model. Universal filters “will do if you’re lucky” are not the best choice. A high-quality product always has clear markings, straight welds and a high-quality rubber seal that should not harden in the cold.
The replacement process is simple, but requires adherence to technology. After draining the old oil, it is necessary to wipe the seat on the engine from dirt. It is recommended to fill the new filter one third full with fresh oil and lubricate the sealing ring with it. This will ensure a tight seal and prevent a dry start when first started.
The filter should be tightened by hand, without using keys, until the rubber gasket touches the plane, and then tighten another 3/4 or 1 turn, as indicated in the manufacturer’s instructions. Over-tightening can distort the seal or strip threads, while under-tightening will cause leaks. After installation, be sure to check the oil level and the absence of leaks after starting the engine.
Following these simple rules will allow you to be confident in the reliability of the power unit. Remember that regular maintenance is the cheapest way to extend the life of your car.
Can the oil filter be washed and reused?
Absolutely not. The paper base of the filter is destroyed when you try to wash it, and the trapped microscopic particles cannot be washed out completely. Repeated use will immediately contaminate the new oil and risk engine failure.
Does the filter brand affect engine performance?
Yes, it has a significant impact. Original filters and high-quality analogues (Mann, Mahle, Bosch) have precisely adjusted bypass valves and high-quality paper. Cheap Chinese analogues often do not have valves at all or have too high opening pressure, which is dangerous for the engine.
How often should you change the engine filter?
The standard interval is every 10-15 thousand kilometers, simultaneously with an oil change. However, when operating in difficult conditions (city, dust, short trips), it is better to reduce the interval to 7-8 thousand km.
What happens if you install a filter with a different valve pressure?
If the opening pressure is higher than normal, the filter may not open during a cold start, causing oil starvation. If it is lower, dirty oil will enter the engine ahead of time without being properly cleaned.