What is the difference between full flow and bypass oil filter?

The differences between various lubricating oil filters on the market today may be unclear. As for which type is the most suitable, there are different opinions in the industry. The most common three types of lubricating oil filter designs are full flow, bypass, and combination.

Full flow filtration

The full flow filter is the most common type, which first processes and cleans all engine oil before pumping it into the engine. The full flow filter provides basic engine protection, which must capture and adsorb pollutants and have sufficient pollutant holding capacity to meet maintenance cycle requirements.

Bypass filtration

The bypass filter element does not directly supply clean oil to the engine, but is used as a separate bypass or renal circulation device, usually only handling a small portion of the total oil flow. The bypass filter element also has the additional advantage of increasing the engine oil capacity. Before the oil flows directly back to the oil pan, efficient filter media is used to fine filter the oil. This process can improve the cleanliness of the engine oil without affecting the oil flow through the engine.

Two level/combined filtering

Some manufacturers have introduced two-stage (combination) filter designs with the aim of combining the advantages of full flow and bypass filters. This two in one design significantly increases resistance, leading to shortened filter life and decreased cold flow performance. Poor cold flow performance can cause the bypass valve to remain open for a long time, causing the engine to lose clean oil during startup and temporarily unprotected. This can lead to increased engine wear, resulting in premature repairs or even engine replacement. Another disadvantage of a two-stage filter is that the bypass section with higher filter efficiency itself has greater resistance, causing most of the oil flow to have to flow through the lower efficiency full flow filter material from the beginning. This means that the oil delivered to the engine is dirtier and lasts longer. Only after the filter element adsorbs enough pollutants, will the oil flow through the more efficient bypass filter material increase.

The two-stage filter element is often mistakenly referred to as a bypass filter element, but it cannot be confused with lubricating oil filters that have an integrated bypass valve or belong to the kidney circulation bypass filter element.

Bypass valve

The engine lubrication system requires the use of a bypass valve to ensure that the oil flow from the oil pan to the engine is not interrupted. The bypass valve is built-in to the filter head or filter body. No matter where it is located, the bypass valve should remain closed for the longest time to ensure that all oil flow is cleaned through the filter element. In cold starts where the engine oil is in a viscous state, or when the filter material is blocked by pollutants and it is difficult to handle the full oil flow required by the engine, the bypass valve should be opened.