Which oil filter strikes the best balance between performance, cost and longevity? To find the answer, you may want to view the oil filter as a type of insurance policy.
"No contractor needs an oil filter," says Bert Elfers, director of product management, Baldwin Filters. "What they need is protection for their equipment. If it ran fine without filters, they would be satisfied. That said, they are really shopping for the best insurance to keep their equipment operating and generating money."
Filter selection tips
Do not match replacement filters only by dimensions. The internal components and specifications can be different. Some important differences include the use of anti-drain-back valves, bypass valves, post seals, varying media types and a range of burst or collapse pressure ratings.
"In general, if the OEM filter had certain features, such as a bypass valve or an anti-drain-back valve, you want to make sure you maintain those same features," says Keith Bechtum, engine liquid filtration group, Donaldson.
"The OEM has balanced the trade-offs of things like oil starvation vs. unfiltered bypass flow," says Elfers. "Choosing to ignore their recommendation is flirting with disaster. OEMs publish specifications for the filters, including efficiency and capacity. There are less notable factors, such as burst, element collapse or bubble point, pressure drop and even can thickness. The best way to ensure a replacement filter meets the OEM demands is to buy a brand that has built its reputation on meeting or exceeding OEM requirements."
The type of media used really determines filter performance and cost. "Cellulose filters are the most common because they provide the most value," says Elfers. "They have long life with moderate efficiency at an attractive cost. Synthetic media drives up the efficiency, but at the expense of contaminant holding capacity and cost."
Decisions on the best compromises must be made. "Efficiency, capacity and restriction all must be balanced in a given envelope," says Elfers. "Opting for a higher efficiency will increase restriction and shorten life unless more media surface is added. Filter capacity is based on the restriction imposed on the system. Most tests establish a 20-psi pressure drop as the point at which a filter has reached its capacity. A higher efficiency filter will have a higher initial restriction. It will plug faster because it will filter out smaller contaminants, resulting in shorter life."
But switching media changes the efficiency/flow restriction equation. "In general, the tighter efficiency filter will have a higher flow restriction and a shorter life," says Bechtum. "The way you change that game is to change the type of filter media you are working with, such as using a synthetic media. You can get better efficiency for a given pressure drop." The downside is synthetic filters typically cost roughly twice as much as a standard filter.
Despite the added cost, synthetic media is typically your best option when it comes to severe conditions or extended change intervals. It has other advantages, as well. "The engine vibrates as you are driving," says Bechtum. Oil surges are also created upon startup. These can dislodge contaminants in the filter. "A contaminant has a tendency to either pass through a cellulose media or slough off of it. It doesn't do that to the same extent with synthetics."
Some filters offer a combination of cellulose and synthetic media. This provides some, but not all, of the benefits of a synthetic at a lower cost point.
It is the capacity that determines oil filter life expectancy. "Excess capacity is wasted if filters are changed before reaching capacity," says Elfers. "On the other hand, running out of capacity before a scheduled change interval can result in the bypass valve opening and allowing unfiltered oil to the engine, or even collapsed elements with catastrophic failure."