Neither Fleetguard nor Donaldson is universally better. Both are top-tier OEM-grade filter manufacturers. Fleetguard is the Cummins-owned OEM brand, optimized for Cummins engines (ISX, ISX15, X15, ISB6.7, ISL9) and using NanoNet synthetic media on premium part numbers. Donaldson is independent and supplies multiple OEMs across Class 8, with a broader catalog covering Detroit Diesel, Volvo, Mack, PACCAR, and International alongside Cummins. For a Cummins-only fleet, Fleetguard is the natural OEM match; the Cummins service kit will already specify Fleetguard FF, FS, LF, and AF series. For a mixed fleet running multiple engine families, Donaldson's cross-engine catalog simplifies sourcing into one supplier. Both have proven micron ratings, dust-holding capacity, and durability under heavy-duty service. The choice usually comes down to fleet preference and dealer relationships, not filter performance.
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