The oil filter is a core component in the lubrication system of a car engine. It is often metaphorically referred to as the "kidney" or "gas mask" of an engine. Its main function is to continuously clean the engine oil, intercept harmful pollutants such as dust, metal particles, carbon deposits, and sludge, prevent these impurities from circulating inside the engine, protect precision components from wear and tear, extend engine life, and maintain optimal performance.

Core working principle
Oil filters typically consist of a casing, filter element, sealing ring, and valves (such as bypass valves and check valves). The workflow is mainly divided into the following stages:
Inhalation and filtration: When the engine is running, the oil pump extracts oil with impurities from the oil pan and presses it into filter 2. The engine oil passes through the filter element (usually made of folded paper or synthetic fibers), and solid particles larger than the filter aperture (such as metal shavings and carbon particles) are intercepted on the surface of the filter material.
Clean reflux: The purified clean engine oil is re delivered to key moving parts such as the crankshaft, camshaft, and piston through the central oil outlet, providing lubrication and cooling.
Emergency protection (bypass valve): When the filter element is severely clogged due to long-term use, causing excessive resistance to oil flow, the bypass valve (overflow valve) will automatically open at a specific pressure. At this point, unfiltered engine oil will flow directly into the engine to ensure that the engine does not suffer catastrophic "dry grinding" damage due to oil shortage in extreme situations.
Cold start protection (check valve): After the engine is turned off, the check valve (backflow suppression valve) can prevent the oil in the filter from flowing back to the oil pan, ensuring that the engine can receive oil lubrication as soon as possible during the next cold start.

Common types and materials
Modern cars commonly use full flow oil filters, which means that all oil entering the main oil passage must be filtered. According to the installation form and material, it is mainly divided into:
Integrated (rotary) machine filter: with a metal casing, the entire filter needs to be unscrewed for replacement. The advantages are good sealing and quick replacement, which are extremely common in Japanese, American, and domestic brands.
Split type (filter element type) machine filter: The outer shell is mostly made of plastic material and fixed on the engine. During maintenance, only the internal paper filter element and sealing ring need to be replaced. This design generates less waste and is more common in European car models.
Filter material: Currently, the mainstream is paper filter, and some high-end or special-purpose vehicles may use synthetic fiber or resin filter to achieve a better balance between filtration accuracy and oil flow rate.

Maintenance and replacement suggestions
The oil filter is a periodic consumable part, and as the usage time increases, the filter element will gradually become clogged, resulting in a decrease in filtration efficiency.
Replacement principle: When changing the oil, the oil filter must be replaced at the same time. If only the oil is changed without changing the filter, the dirt in the old filter will quickly contaminate the new oil, resulting in a significant reduction in lubrication effect.
Replacement cycle: It is usually recommended to replace it synchronously with the engine oil. For ordinary family cars, the general cycle is to replace them every six months or every 5000 to 10000 kilometers of driving; If fully synthetic engine oil is used and paired with high-quality filters, the replacement cycle can be appropriately extended to 8000-10000 kilometers. Please refer to the owner's manual for each vehicle model for specific instructions.