There are two ways to measure filter efficiency – single-pass and multi-pass. Which test do you think better represents real-world oil filtration – a single-pass test that runs just 45 gallons of oil through a test filter, or a multi-pass test that passes more than 2,500 gallons through the filter? Why it’s the multi-pass test of course. But won’t a filter that’s more efficient get clogged sooner, causing the bypass valve (if the filter has one…) to open and direct unfiltered oil to the crankshaft, bearings, and other critical components? Ah, that brings us to what the filter engineers refer to as capacity. Capacity represents the amount of contaminants a filter can remove and hold before flow is restricted. Capacity is usually measured in grams. Some filter makers don’t advertise capacity if it’s not a favorable number for them. In the case of Purolator PureONE oil filters, they have a capacity of at least 13 grams. In real-world terms that means that a PureONE filter will hold the equivalent of 31 standard-size paper clips before it becomes blocked. And that’s a whole lot of debris. Beyond efficiency and capacity, there are other features you should look for in your choice of an oil filter – things like a steel center tube for reliable support of the media, a one-piece anti- drainback valve (less likely to leak than a multi-piece design), and a flat sealing ring, shown by SAE tests to provide greater sealing surface area, higher blowout resistance, and longer life than O-ring or P-ring designs. Purolator oil filters provide all this and more. Some filter companies use paper or felt end caps versus the steel end caps used by Purolator. In cold climates where cold start-ups can cause huge momentary spikes in oil pressure, you should look for a filter design that’s been tested for burst strength. Our Purolator expert tells us that Purolator Classic and PureONE oil filters, for example, are tested 25,000 cycles at pressure pulses of 0-100-0 psi to validate filter housings’ mechanical strength. And that’s the real spin on oil filters and how they work!