While engines, especially light-duty diesel engines, have become far more advanced over the years with the addition of high-pressure common-rail direct injection, sophisticated turbocharging, and ever-tightening tolerances, there’s one vital system that has remained relatively unchanged. Oil filtration technology hasn’t progressed at a rate that’s consistent with the engines these filters are protecting. The basic premise of a paper filter in a steel can dates back to the very earliest days of modern internal combustion engines and is still in use today. While some companies have made improvements in the filter element department, you can still by cheap units at the local parts store that are no different from those your grandfather used.
It’s no secret that clean oil is key to engine longevity. Studies have shown the majority of normal internal engine wear is caused by particles that range in size from 5 to 25 microns. However, to maintain adequate oil flow and pressure, even the best oil filters only scrub particles that are about 20 microns or larger. Fortunately, there’s a solution to this issue, and it lies in bypass filtration.
How it works is simple: A small percentage of the engine’s oil is routed to a secondary filter, bypassing the full-flow filter, before being returned back to the engine. This second filter features an element that collects particles as small as 2 microns and returns oil that is analytically clean of debris. These filters work exceptionally well at removing soot, which proves invaluable to diesel engines. Since these filters only pull off about 10 percent of the engine’s oil, there’s no detriment to pressure or flow, and the superclean oil means that not only can oil change intervals be significantly lengthened, but engine life is extended as well.
| While Amsoil offers all the pieces individually to build your own custom setup, if you happen to own a Cummins, Duramax, or Power Stroke diesel, there’s a premade kit just for you. Our BMK-32 kit came with everything necessary to install the bypass filter on our ’02 Silverado 2500HD.
In an effort to help protect our freshly built LB7 Duramax, we turned to the experts at Amsoil. While Amsoil is best known for its synthetic fluids, it also produces a line of filtration products that includes engine oil bypass filtration kits. Best of all, the company has kits specifically designed for Duramax, Power Stroke, and Cummins diesels. We opted for the BMK-32 single-bypass kit. Amsoil offers a dual-bypass kit, BMK-27, which moves the full-flow filter off of the engine and onto the head unit that also houses the bypass filter. There is a school of thought that leaving the full-flow filter in place reduces the risk of having a drop in oil pressure and flow through the engine, so for this reason we opted for the single-bypass kit, which leaves the full-flow filter in place and sources oil for the bypass filter from a small sandwich adapter. When asked about the difference between the kits, Amsoil told us both are equally effective when installed properly, and the main difference lies in how the filters are mounted, with the dual kit taking up more space in already cramped engine compartments.
From start to finish, our installation took about two hours, and we were able to complete it in the driveway with basic handtools. We paired the bypass unit with an Amsoil full-flow filter and the company’s Signature Series diesel oil. Using Amsoil’s oil analysis service, people have reported oil drain intervals most would describe as ludicrous. Once we’ve racked up a pile of miles on the system, we’ll send an oil sample in for testing and report back the findings. Stay tuned!
| The one area Amsoil falls short is in providing mounting guidance for the filter head. We turned to the aftermarket and picked up a bracket made for our truck and designed to support Amsoil’s BMK-27 dual-bypass filter. We really appreciated the sticker included with the kit that showed where to drill holes to mount the filter head.
| A quick tap with a punch and three holes later, and our BMK-27 bracket was now BMK-32 compatible. Note to the aftermarket: It’s easy for one bracket to do both. You’re welcome.
| Amsoil Bypass Filter Drilling Holes
| Since the kit ships as a collection of pieces, each of the fittings needs to be installed. Amsoil’s kit is complete with everything needed, right down to special thread sealant for the fittings.
| Before tightening the fittings on the filter head and full-flow sandwich adapter, it should be noted which way these fittings need to face for proper hose alignment. Once orientation is determined, the fittings are placed finger tight, plus two to three turns.
| Amsoil Bypass Filter Fittings
| A heavy-duty rubber O-ring seals the sandwich adapter to the engine, and a light coating of oil prior to installation is necessary to ensure proper installation.
| Working on our four-wheel-drive Silverado proved tight when it came to torquing the adapter to the required 40 ft-lb. Take care to ensure the adapter doesn’t rotate into a position where the previously installed hose fitting is inaccessible.
| Amsoil Bypass Filter Adapter
| With the sandwich adapter in place and a mounting location for the bypass filter chosen, you can measure the length of hose required to connect the two. Be sure to leave a few extra inches to account for engine and chassis flex.
| If you don’t already have a good set of hose shears, now is the time to go out and get them. A clean square cut is imperative for proper sealing of the hose fittings, and your kitchen scissors aren’t quite going to cut it here.
| Assembling the hose fittings may seem like a daunting task, but it’s rather simple. Start by screwing the outer nut counterclockwise onto the hose until it bottoms out. Then, after applying a liberal amount of oil or other lube, screw the tapered nipple into the socket until it bottoms out as well.
| Amsoil Bypass Filter Hose Assembly
| Before installing the bypass filter element, it should be filled with oil to prevent an excessive dry start. Our filter consumed half a quart of Amsoil’s Signature Series 15W-40 diesel oil.
| Our bypass filter is mounted to the inside of the driver-side framerail. This spot keeps the filter tucked up and out of the way of damaging road debris.
| With the bypass filter element fully installed, it’s crucial to ensure the feed lines are routed out of the way of anything that moves or is hot or sharp. For an added level of protection, we covered ours with Titanium Protect-A-Sleeve from Design Engineering Inc. This shielding protects from 1,800 degrees of direct heat and up to 2,500 degrees of radiant heat.
| Once oil has made its way through the bypass filter, it is returned to the engine by way of this trick billet-aluminum oil filler cap replacement. We’re not fully sold on running 6 feet of hose for the return, but Amsoil reps say they’ve never heard of an issue arising from this setup when routed properly.
Amsoil Bypass Filter Kit
Part #: BMK-32
Part #: 010475B