The difference between oil filters.

Various types of engine oils are used to reduce friction between the moving parts of engines and machinery. Over time and as fuel is consumed, the oil becomes contaminated with wear products of the oil itself and the running engine, which contributes to its premature wear. To prevent this from happening, the oil is constantly purified by oil filters during operation. They are classified into three main types, which differ from each other in the way they filter the oil.

What are the oil filters

Full-flow oil filter is a filter connected in series to the main oil line, which once passes all the engine oil sucked in by the oil pump.

Partial flow oil filter is a filter connected in parallel to the main oil line, which repeatedly passes part of the engine oil through it.

Combined oil filter assumes combination of full-flow and partial-flow oil filters in one device.


The simplest design full-flow oil filter from the moment the engine is started immediately passes all the engine oil through it, simultaneously flowing to all zones requiring lubrication. Such a scheme, in comparison with others, cleans the oil faster, but also fills the filter faster. This is why a bypass valve plays an important role in a full-flow oil filter. It is triggered when there is a significant pressure difference between the untreated and cleaned volumes of oil due to contamination of the filter element. In this case, the oil enters the engine uncleaned, but its lubrication is provided, which means that failure from overheating is prevented.

A partial flow oil filter located in parallel to the main oil line filters only a small portion of the engine oil at a time. The big one at first enters the engine without filtration. However, this small volume passes through a parallel circuit many times, therefore, the degree of its purification is much higher than that of a full-flow filter. Gradually, the entire volume of the poured engine oil is also cleaned with high quality, although this takes much more time. In terms of the degree of engine protection, full-flow and partial-flow oil filters are approximately equal, but the latter has a significantly lower risk of pressure drop due to contamination of the filter element.

The design of a combined oil filter implies the placement of two filters on the oil line at once - full-flow and partial-flow. The volumes of engine oil passing through them are in a ratio of 9: 1. The degree of oil purification is close to complete, which automatically increases the resource of the engine, engine oil, and oil filters. Most often, this type is used on diesel engines of trucks and construction equipment.


  1. A full-flow oil filter passes the entire volume of oil through itself once.
  2. It is simpler in construction.
  3. The filter element of the full-flow oil filter becomes dirty more quickly.
  4. The partial flow oil filter repeatedly passes a portion of the oil volume through it.
  5. This device cleans oil much slower than full-flow, but better.
  6. The combination oil filter contains full-flow and partial-flow filters.
  7. It cleans the engine oil almost completely - faster and better than full-flow and part-flow filters.

Which oil filters are better? We discuss in the comments!