Wix Filter/NapaGold Oil Filter vs MicroGard

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The MicroGuard filter is the lesser priced filter found at O’Reilly Auto Parts; it is more comparable to the Napa ProSelect (tested here) than the NapaGold or Wix.

  • MicroGuard uses a leaf spring rather than a coil spring; the leaf spring must always seat properly onto the end cap. Additionally, a leaf spring can bend under high pressures. However, the MicroGuard was the ONLY FILTER to have a built-in bypass valve which could let non-filtered oil into the engine.
  • MicroGuard uses weaker fiberboard end caps rather than the metal ones. The center tube of the MicroGuard is not secured to the filter media or the endcaps. Excessive glue was found where the pleats meet the fiberboard.
  • The filter media inside the MicroGuard was crimped to itself, rather than glued.
  • MicroGuard does not use a phenolic resin which helps to bind the media and protect during high temperatures.
  • The center tube of the MicroGuard filter is a spot-welded, straight seam; other brands use a spiraled center tube for better flow.
  • The _ filter uses a rubber anti-drain back valve that sits loosely in the center tube. The anti-drain back valve is used to prevent oil from draining back to the crankcase after shutdown. A silicone valve is less likely to break down during high heat than the nitrile rubber.


  • Excessive glue was found where the pleats meet the fiberboard.
  • The MicroGuard had holes on both ends of canister; the leaf spring was used to stop the flow from the top of the filter.
  • The MicroGuard filter had the lowest number of pleats at 34.
  • The MicroGuard filter tied the Fram for the shortest of all the media at 47".