It was the papers explanation of why they chose not to use a bypass filter but the Fram full flow for gas engines.
The paper stated that non of the manufactures "claimed" to be able to extend the OCI for a gasser. Using only a slightly extended OCI didn't pencil out for being cost effective:
Passenger Car Filters
Passenger cars and light trucks are a large portion of the vehicle market. They comprise the majority of private vehicles in the state. An estimated 61 percent of all California vehicles are passenger cars. Meanwhile, light-duty trucks account for 32 percent, with the remaining 7 percent comprised of all medium and heavy-duty trucks. Potential oil savings could be substantial if a suitable filter was found for passenger cars. However, there are few HE oil filter designs claiming to extend oil drain intervals for passenger cars.
Each filter manufacturer underwent substantial research by DTSC staff. This included phone calls and website reviews of major auto supply stores. Staff found several high-end, spin-on filters that contain synthetic media and reinforced structure. However, the Fram X2 Extended Guard, a traditional, spin-on, full-flow filter design, was the only filter located by DTSC that claimed to extend oil change intervals. Its manufacturer claimed an extended 7,000 miles oil-and-filter change interval because of the reinforced, synthetic nylon fiber construction. Its single pass efficiency is approximately 96 percent at 10-20 μm, slightly lower than the 98 percent attributed to other high-end, spin-on filters.
The major manufacturers (Champion, Fram, Purolator, and Wix) also produce most of the fullflow filters that carry other brand names. Many of these “off-brands” are premium filters designed for extra engine protection or heavy duty use. However, during filter selection, staff learned these filters did not claim to extend oil drain intervals beyond the auto manufacturers’ recommendations.
Subsequently, some filter marketers (e.g., Mobil) now offer new products for extended change intervals. Mobil’s filter claims a 15,000-mile extended oil change interval provided Mobil 1 Extended Performance synthetic oil is used. Although synthetic oils have shown growing promise in extending oil changes, they were not part of this study.
Staff also discovered a filter that features a cleanable and reusable screen. This full-flow filter has a metal mesh screen with larger pore sizes than typical bypass filters. Reusable screen filters must be cleaned with a suitable solvent, which generates an additional waste stream. This filter was not included in the study because it was not designed for extended oil drain intervals.
Staff considered bypass filter testing on cars. These smaller-size bypass filters ranged in price from $75 to $122, with filter elements costing from $10 to $15. Even the less expensive of these filters remained too costly to justify an automotive application. The Fram X2 Extended Guard was the only auto-tested filter. Its particle removal efficiency is less than that achieved from bypass filtration. However, marginal oil drain extensions could make an impact since autos generate a large amount of waste oil. By the end of the project, Mercedez-Benz, BMW, Honda, and GM were using oil life sensors, and Ford extended its recommended oil change intervals by 50 percent, from 5,000 miles to 7,500 miles. 12
