Everything You Need to Know About Oil Filters

Wow, you really have been saving up oil filter questions for 50 years, Randy. I'm glad you didn't wait another 10 years or I'd have to take over the Real Estate section to finish this answer.

The reason there are so many different filters is because engines are all different. And space is at a premium. Most engine compartments I work on these days have no room to spare. So when designing an engine, all the immovable parts are designed first. Then later in the process, they find a place for the filter, preferably right on the engine block. In order to fit oil filters into the nooks and crannies manufacturers ultimately allot for them, filters have to come in all different shapes and sizes.

Generally speaking, more expensive filters are better than cheap ones, because they use better filtration materials. Instead of plain old Charmin, filters now use materials like synthetic glass microfibers, which do a better job of filtering the oil. That's also why smaller filters can be used. With better filtration materials, they can provide all the filtration the engine needs in a smaller volume.

We tend to stick with OEM filters -- the filters made by the car's manufacturer. You can never go wrong with those. Modern filters also have check valves, which explains why the oil doesn't drain out of your Subaru filter, even though it's mounted upside-down. Without a check valve, the oil would drain out, and that would be a problem. If the oil drained out, every time you started your car, your oil pump first would have to fill the oil filter, leaving other parts under lubricated for those first few crucial seconds that the engine is running. But the check valve keeps the filter full and completely solves that problem.

So, basically, Randy, there's nothing to worry about. Stick with a Subaru filter or other quality brand, and you'll get all the filtration you need. I'll look forward to hearing from you in 50 years.

Most organizations that manage mobile equipment fleets are far too casual about controlling particle contamination in engine oil. They seem to have blind faith in the effectiveness of standard-purchase oil filters and air filters to achieve their reliability objectives. Many don't have a clue how well their filters are performing as evidenced by the fact that they don't set target cleanliness levels for crankcase oils and don't ask their oil analysis labs to report cleanliness levels.

This graphic above helps illustrate the many and compounding ways particle contamination costs fleet organizations real money. The many opportunities for cost reduction are also clear.

1. The process usually begins with organizations pretending to save money by buying cheap oil filters and air filters with the false sense that all filters are pretty much the same.

2. In fact they are not, as you often get exactly what you pay for. Buy cheap filters and you usually get increasing and excessively high dirt loading in the lube oil over the drain interval. High dirt concentration shortens oil life and performance in numerous ways. One is by ...

3. The excessive amounts of wear debris that dirt generates in the oil from abrasion and surface fatigue. The wear particles are catalytic and cause premature additive depletion and base oil oxidation. Engines only permit so much wear debris to be generated (like tread on tires), after which the engine will need to be rebuilt. The short oil life and engine rebuild interval is both costly and unnecessary.

4. High engine wear in the vicinity of the combustion chamber (cylinder walls, rings, piston, valves, etc.) leads to poor combustion efficiency. This translates to less work performed due to the engine's sluggish/slower operation. Additionally, it causes ...

5. ... a rapid loss of fuel economy (more fuel consumption) and oil economy (more rapid oil burn). These are serious operational costs to a fleet organization.

6. When more fuel and oil are burned there is a correspondingly high discharge of tail pipe emission. This results in an unnecessary penalty to our environment and puts human life in danger.