The real problem is soot. Diesel engines make it, some of it gets trapped in the DPF, and some of it gets past the rings into the oil. Once it is in the oil, it works against the additive package and keeps circulating through the engine. That gets worse when the truck is worked hard, which is exactly why severe-use oil change intervals are shorter. A conventional full-flow oil filter has to pass the engine’s entire oil supply, so it cannot be extremely fine without becoming restrictive. That is why the finer contamination stays in the oil. A bypass filtration system solves that by taking a small amount of pressurized oil, filtering it much more tightly, and returning it to the sump. In this case, the filter is rated 98.7% efficient absolute at 2 microns, and it handles less than 5% of pump output, so it cleans the oil without starving the engine. If you tow, hotshot, haul a camper, or spend long hours under load, this is the kind of filtration that makes sense. Cleaner oil means less soot circulating through the engine and a better shot at extending oil life without guessing.
Gale Banks opens with a story from around 1970, when Banks was deeply involved in marine gasoline engines. Oldsmobile approached the company to build an endurance racing version of its 455 V8 for jet boat competition. The challenge was substantial: the 455 had been designed as a mid-range passenger-car engine, suited to a large car that spent its life loafing along, not an engine expected to survive 5,200 RPM for as long as nine hours at wide-open throttle in the Parker 9-Hour Enduro.
At the time, Oldsmobile had already tried to turn the engine into a competitive boat-racing package through another builder associated with drag-racing Oldsmobiles on the West Coast. That effort had run into serious durability problems. According to Banks, they could not even keep the engine alive through a 20-minute sprint race. A magazine contact familiar with Banks' work suggested Oldsmobile bring the project over, and Banks took it on.
Banks built a 455 Oldsmobile-powered jet boat using a Jacuzzi jet drive. The boat carried the number 455 and was named Nice and Easy, reflecting what he describes as a laid-back approach to the project. Driven by Barry Lieberman of Hardin Marine in Anaheim, the boat proved successful immediately.
Banks says the team won both the APBA jet boat championship and the NJBA National Jet Boat Association championship. They then took the same package to Parker, Arizona, for the Parker 9-Hour race and won their class there as well. That success established Banks' credibility with Oldsmobile and led directly to a later conversation about diesel engine development.
After the racing success, Oldsmobile decided it wanted to build a diesel engine for use in Oldsmobile passenger cars and GMC pickup trucks. Banks was asked to speak with the diesel program engineers, and he says he gave them several specific warnings. First, he told them the engine needed more head bolts because the planned design, at roughly 16:1 compression ratio, would blow head gaskets. Second, he said it needed four-bolt main bearing caps because the crankshaft would fail otherwise. Third, he recommended a roller-tappet camshaft because soot contamination in diesel oil would destroy the zinc dithiophosphate anti-wear package in the oil.
He explains that zinc dithiophosphate was the extreme-pressure lubricant additive used at the time, and that modern versions of the same chemistry are still used today. In his view, soot in the oil attacked the oil's protective capability, making the flat-tappet valvetrain especially vulnerable. Banks says the Oldsmobile 350 diesel ultimately failed in exactly the ways he predicted: crankshaft problems, head-gasket failures, and flattened camshafts.
Banks describes the Oldsmobile 350 diesel as one of the most notoriously unreliable engines of its era. In his telling, the engine did more than fail mechanically; it damaged the entire idea of diesel passenger cars in the United States. He argues that the reputation hit was so severe that Mercedes-Benz stopped importing diesel cars into the U.S. for six years because buyers no longer wanted them.
The eventual correction, he says, was to abandon the 350 diesel entirely. GM then developed a purpose-built 6.2-liter V8 for Chevrolet and GMC pickups beginning in the early 1980s. That historical example sets up his main point for the episode: soot contamination in engine oil has long been a fundamental diesel problem, and even modern engines have not eliminated it.
Banks emphasizes that soot remains the enemy of engine oil. Even current diesel engines still produce soot, and some of it inevitably gets into the crankcase oil. He points to the owner's manual for his 2019 Ford test mule, which specifies a normal oil-change interval but also recommends more frequent oil changes when the truck is used for heavy towing or hard work. His interpretation is that harder operation produces more soot. Some of that soot exits through the exhaust and is trapped by the diesel particulate filter, but some also gets past the piston rings and enters the oil.
When he checked the oil in the truck, still on its factory fill and overdue for replacement, he found visible soot contamination. That observation led him to revisit a topic he had heard about for decades but never personally tried: bypass oil filtration. Conventional full-flow oil filters, he says, typically filter only down to about 20 microns. That leaves a large amount of much finer soot circulating in the oil.
To evaluate the condition of the oil properly, Banks contacted AMSOIL and requested a bypass filtration system for the 2019 Ford. Along with the hardware, the shipment included an oil analysis pump kit and prepaid oil analysis supplies. He highlights the sampling method as important. Rather than draining oil from the drain plug, which can pick up settled material from the bottom of the pan and distort the sample, the kit draws oil through the dipstick tube.
The sampling setup uses a vacuum pump and a threaded sample bottle so oil can be pulled directly from the sump in a way that is more representative of what is actually circulating in the engine. Banks treats that as the correct way to establish a baseline before installing the bypass system. Although he spends some time noting the extra AMSOIL products included in the shipment, the technical takeaway is that oil analysis and proper sampling are part of understanding whether soot contamination is being controlled.
Banks then walks through the bypass filtration hardware itself. The AMSOIL filter is described as a two-stage, pleated and layered construction with a fully synthetic media and a marine powder-coated shell. Its rated efficiency is 98.7 percent absolute at 2 microns under ISO 4548-12. Banks remarks that the media is refined enough that it resembles what might be used in a diesel fuel filter.
The hose supplied is Parker air-brake hose with a 500 PSI working pressure. Since engine oil pressure is typically in the 50 to 100 PSI range, he notes that this provides a five- to ten-to-one design margin. The kit also includes a spin-on adapter that mounts where the stock oil filter normally goes; the stock oil filter then spins onto that adapter. A 1/8-inch port on the side provides the high-pressure oil feed to the bypass filter.
For the return side, the kit appears to use a replacement oil-fill cap assembly. Banks notes that it has machined ramps so it twists in and seals like the factory filler cap. The filtered oil returns through that fitting back into the engine. The package also includes the filter mount, hose ends, swivels, tie wraps, threadlocker, and mounting hardware, which he praises as a complete industrial-grade installation kit rather than a partial package that requires extra trips to the hardware store.
Banks explains the oiling system in stages. In a normal engine, oil is drawn from the sump into the pump, sent through the full-flow filter, and then distributed to the engine's bearings and other lubricated components. Oil pressure is measured in the line between the filter and the engine bearings. After lubricating the valvetrain, piston skirts, wrist pins, and related parts, the oil drains by gravity back into the sump.
The bypass system taps a small amount of that already pressurized, full-flow-filtered oil from the high-pressure side. In this AMSOIL setup, the bypass circuit handles less than 5 percent of the pump's output. That small stream is routed through the very fine bypass filter and then returned to the sump. It is called a bypass system because that oil bypasses the engine bearings and the rest of the engine's immediate lubrication path; it is cleaned separately and then returned to the oil reservoir.
Inside the bypass filter, Banks describes the flow path as entering from the outside through ports, moving through the filter media toward the center, and then exiting through a control orifice that regulates flow rate. Because only a small fraction of total oil flow is diverted, the system can use extremely fine media without starving the engine of oil.
Banks is careful to define the intended application. He says this kind of bypass filtration is designed for work-truck use: hotshot hauling, towing a big trailer, carrying a camper, or climbing long mountain grades. In those conditions, the engine spends more time under load, which means more throttle, more combustion loading, and more soot production. He specifically says he would not use this setup on a racing engine, where the operating environment is different and the engine is being pushed much harder in a different way.
For modern diesel trucks, he notes that manufacturers have tuned engines to reduce soot output, partly to help fuel economy and efficiency and partly to reduce loading on the diesel particulate filter. Even so, the DPF still captures soot and periodically regenerates to burn it off, which confirms that soot is still being produced. Some of that soot still reaches the oil.
His conclusion is that a bypass filtration system can remove the fine soot particles that conventional filters miss and therefore allow oil-change intervals to extend well beyond the standard recommendation. More importantly, he sees it as long-term protection for owners who plan to keep a diesel truck beyond the warranty period. In his view, for that kind of ownership, bypass filtration is inexpensive insurance against soot-related oil degradation and wear.