The Story of Filters

The 1940s saw the introduction of filtering systems on mass-produced automobiles, and the 1960s saw the introduction of disposable “spin on” oil filters, making oil filter changes much more convenient. Over the next few decades, improvements in the internal architecture and filter material increased the efficiency of the filters significantly. Today, all vehicle engines, whether gasoline or diesel, include filtration meant to increase the cleanliness of the engine’s oil and hence lengthen its life.

What distinguishes modern filters from their predecessors is the filter media itself. To prevent particles from entering the system, early designs utilized steel wool, wire meshes, and metal screens. The following media iteration was in the form of bulk cotton or various woven fabrics, such as linen.

Earlier vehicle engines lacked any form of oil filtering. It was not until 1923 that Ernest Sweetland and George Greenhalgh received a patent for their device, the “pure oil later” or “Purolator,” that an automobile with a full pressure lubrication system became available.

It would be many years later before a full-flow oil filter was included in today’s autos.

When disposable filters became popular in the 1960s, they were manufactured using cellulose and paper to keep production costs low. While cellulose and paper filters are still available today, more advanced technology exists in synthetic media.

Filters manufactured today are composed of cellulose or synthetic media and housed in a steel container. The top of the filter features a threaded center hole surrounded by smaller holes. Oil enters via the surrounding holes, travels through the medium, and exits by the threaded center. The container is normally screwed directly to the engine block and is sealed with an O-ring gasket.

Additionally, some filters include a drain back valve at the smaller surrounding holes to prevent dirt and debris trapped on the media’s face from washing back into the system during depressurization. Additionally, there is a pressure relief or bypass valve that allows oil to bypass the media in the case it becomes clogged, or the pressure differential becomes excessive.

A good filter has a strong steel that can withstand the high oil pressure, an anti-drain back valve that functions without creating excessive back pressure, a pressure relief valve that does not leak below its opening pressure, and a strong element and cap that can withstand the pressure and flow of oil without collapsing.

The element media must be capable of trapping microscopic particles while not obstructing the flow excessively. Cellulose is a material that is used in cheap filters. The paper’s fibers serve as a mesh, obstructing particles while enabling the oil to pass through. Certain manufacturers enhance the efficacy of cellulose by mixing it with other media, such as cotton.

Additionally, there is synthetic fiber media for high-end filters that has smaller passageways to trap smaller particles but can also flow more fluid through due to the increased surface area created by the increased passages.

Additionally, there are media that are a hybrid of the two. Not only the media type but also the construction all contributes to the filter’s ability to remove material. Depth filters are typically made of synthetic material with a gradient in the passage size. In other words, the deeper the oil penetrates the element, the narrower the passageways become. This traps large particles on the top and small particles deeper beneath, allowing the filter to keep more particles before becoming too restrictive.

Therefore, how can you know which ones to purchase? Oil filters for passenger cars account for a sizable share of total sales to do-it-yourself oil changers. This accounted for 189 million oil filter changes last year. Cost is a significant factor in determining which oil filter to purchase.

A synthetic depth filter costs nearly twice as much as a cellulose filter. It may cost a few additional dollars initially, but there have been numerous case studies demonstrating the benefit of oil cleanliness on component life to the tune of three to four times the engine’s life extension.