Neither 2-micron nor 30-micron is universally better; each fits a different position in the fuel filtration system. A 30-micron rating is appropriate for a primary filter or pre-filter, where the job is to catch large particles and let smaller ones pass through to a finer secondary. A 2-micron rating is appropriate for a final filter directly upstream of the injectors, where the goal is to remove anything that could damage injector tips at 30,000+ PSI. Running 2-micron in the primary position causes premature clogging because the filter clogs on particles a 30-micron primary should have caught. Running 30-micron in the secondary position lets too-large particles reach the injectors. The right answer is both, in series: 30 in front, 2 in back. That is the standard architecture on Cummins, Detroit, Volvo, Mack, and PACCAR Class 8 engines.
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