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The benefits of bypass filters are said to be: Minimizes oil change maintenance, downtime and engine wear; extends engine life by removing harmful particles that can distroy vital engine parts on new EGR engines, i.e. being designed to address the acid build-up on oil, improves asset productivity by keeping vehicles in operation longer; and cuts oil purchases and disposal costs. 

These bypass filters are not new, but is now more important for the newer exhaust gas recirculation (EGR) engines that produce more soot. Bypass filtersÕ life expectancy depend on the filterÕs size, its contaminant-holding capacity and the vehicleÕs application, engine mechanical condition and maintenance history. 

They can be installed on virtually every oiling system for both medium- and heavy-duty applications and are available in spin-on, cartridge and centrifugal style, and come in a wide range of sizes to match the systemÕs oil capacity and available oil flow rate. The only limiting factor is the available space for it on the vehicle. 

Bypass filtration accomplishes two factors in lowering operating costs: enabling an extension of oil drain intervals and reduce abrasive wear by removing a much higher percentage of wear-causing particles than a full-flow oil filter is capable of addressing. Originally it was used mainly to extend engine oil life and thereby oil drain intervals and reduce costs. The latest advances in the products have added protection of major engine components from the side effects of EGR and other emissions-reduction techniques. The real value of bypass filtration are the reduction in abrasive wear and increased control of soot levels

The Basics
A basics review - Bypass oil filtration is a type of filtration where a small percentage, about 10%, of  the total flow of the engine oil, is withdrawn and passed through a higher efficiency filter before being returned to the oil sump. Full-flow filters are generally designed to capture particles as small as 25 to 40 microns, while a bypass filter normally captures contaminants down to 5 microns or smaller. 

The remaining 90% of the oil continues through the full-flow filter into the engines components for lubrication, and the oil that passes through the high efficiency filter returns directly to the sump. 

Oil analysis data is the best way to tell if the bypass filter is doing its job. High soot levels indicate that the bypass filter is plugged and not trapping soot. On the other hand, a low soot percentage in the oil analysis data relative to the baseline data indicates that the bypass filter is doing its job. 

Soot and combustion by-products are acidic and create serious challenges in the engine lubrication oil packages. Soot is very abrasive, causing increased cylinder and ring wear, and can increase oil viscosity as the concentration increases.  

Of course, bypass filters have their critics and are not the only way to achieve the benefits of cleaner oil. One alternative solution is to replace the conventional cellulose media found in full-flow filters with synthetic media because it typically has a higher efficiency rating and lower pressure drop than cellulose at a given flow rate. Even so, bypass filters achieve higher particle removal efficiencies than the synthetic full-flow media does in the very small soot-like sizes.   One example of the newer bypass filters is Luber-FinerÕs Zgard 9750 Heavy duty Spin-on Bypass oil filter. It utilizes high-tech composite filter media to protect EGR engines against acid and soot contamination, reducing downtime and extending engine life. The spin-on design makes installation and maintenance quick and easy. 

New design bypass filters are also described as a Soot Removal Device (SRD), by international industry standards for performance testing. Centrifuges are commonly utilized in a bypass mode and are also classified as SRDs. The downside to centrifugal separation is the high rotational speed required to generate a measurable level of particle removal. Centrifuges  only achieve particle separation while the engine is in the medium-high to high rpm operating range. A Soot Removal Device such as the Zgard protects the engine even at idle and during low speed operation. 

Keep in mind that  when extending drains, itÕs important to always follow the engine manufacturerÕs guidelines for change intervals and never extend without using oil analysis. ItÕs even more important than ever since the engine manufacturers may be making changes to traditional drain interval recommendations for the 2007 engines. 

And, up ahead, the new low emissions 2007 engines will bring new challenges to oil filtration systems. Not only will there be exhaust aftertreatment systems, but also the composition of oil change as the API CJ-4 diesel oil classification is here. EGR return rates will increase dramatically with some engine designs, and soot will still be an issue. The CJ-4 oil additive packages will be very different than the CI-4 used today and there may be changes in the recommended oil drain intervals. As always, particulate filtration will continue to be important.

Also, from the diesel fuel side there will be far less sulfur in the fuel. Acid compounds such as sulfuric, nitric, and organic will still be formed as a by-product from combusting fuel.