Understanding Oil Filters

Why Using Only Quality Filters Is Important

Oil filters must performs three key functions at the same time – 1) remove contaminants, 2) hold contaminants without clogging the filter and 3) still allow oil to flow. Cheap filters often perform these tasks poorly and may clog prematurely, which forces open the oil by-pass valve – allowing unfiltered, contaminated oil to flow through the engine until the next oil and filter change.  There is no way to know this is happening.

oil filter by-pass valve from Marine Diesel Basics

from Marine Diesel Basics 2 - How Things Work, Boat Buyer's Guide

coming winter 2017

Functions of an Oil filter

An oil filter has five essential functions:

  • lubrication – pistons and piston rings moving up and down the cylinders 40 times per second (@2500rpm) would instantly destroy themselves with lubrication
  • heat transfer – circulating oil through the engine block transfers heat away from the hottest parts
  • cleaning – microscopic metal and carbon particles get trapped in the oil filter
  • corrosion protection –  inhibitors help protect parts from pitting from sulphuric acid and minimize rust (oxidation)
  • sealing – oil helps seal several moving parts, e.g. between piston rings and cylinder walls.

Buying Quality Oil Filters

There is no easy way to identify top quality oil filters – no standard or ratings printed on the side of the filter or available on a website. Brand claims are just that – with no objective measurements to go along with the marketing. 

  • use the same brands selected by local trucking companies
  • avoid cheap brands using minimal paper elements and often inferior by-pass valves
  • cut open a filter and inspect the element and by-pass valve
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