WHAT EXACTLY DOES THE OIL FILTER DO, ANYWAY?

by Pete The Mechanic

We all know automobiles need oil filters and that they need to be changed regularly, but do we really understand what they do and why they're so important? How often should they be replaced? What can you tell by examining a used filter? How should we dispose of a used filter?

As an automotive technician, knowing the answers to the above questions is important, because it enables us to speak with confidence when we talk to our customers. So, let's take a close-up look at filters and the role they play in protecting the automobile's engine.

AN OIL FILTER'S JOB

In addition to motor oil, every car needs an oil filter to help keep it running. While motor oil lubricates the engine, the oil filter stops the solid deposits from reaching critical engine parts.

These deposits can result in dangerous levels of engine wear. We all know that as oil passes through the engine, it lubricates such parts as the valves, cylinder walls and pistons, camshafts and connecting rod and crankshaft bearings. As the oil flows over these various parts, it picks up small metal particles, dirt and other types of harmful grit. A good motor oil chemically holds these harmful deposits in suspen-sion until it reaches the filter, where the deposits are trapped and removed from the circulating motor oil.

Even though the oil pump pickup tube has a screen that removes large particles, the oil filter is still responsible for most of the filtering. Filter media is designed to trap the most harmful particles--those between 10 and 20 microns--the first time they reach the filter. Wear particles in the 10 to 20 micron size range can be forced through the oil passages of your engine. These dirt particles can rip and gouge bearing and cylinder surfaces.

Test results have shown that particles under 20 microns in size cause far more engine wear than larger size particles. Generally, particles less than 10 microns remain suspended in the oil so wear surfaces in the engine are protected. Large particles (over 20 microns) will not fit in tight engine spaces. They usually remain lodged in crevices, until oil pressure breaks them up into smaller particles. Therefore, a filter that traps and holds more particles in the 10 to 20 micron size offers better engine wear protection.

The contamination in the oil that the filter must remove is produced both inside and outside the engine. Internal contamination is caused by tiny metal particles that normally wear off the moving parts of the engine. External contam-ination is due to the abrasive dust and dirt in the air that enters through the air intake system, as well as the fuel system and its by-products. A top quality filter can handle both kinds of contaminants.

HOW OFTEN SHOULD FILTERS BE REPLACED?

Filters should be changed every time the oil in the car is changed. Oil passes through your engine four times for every mile you drive. By the time you drive 3,000 miles, the same oil has passed through your filter 12,000 times.

Consult the owner's manual for recommended maintenance intervals. To provide greater protection against engine wear, most experts suggest changing your customers' oil every three months or 3,000 miles (2,500 miles with turbo-charged designs and stop-and-go driving styles). A used oil filter contains dirty oil and contaminants, and if the oil is changed but the filter isn't, that dirty oil in the filter quickly adds its load of contaminants to the fresh oil. It's like pouring fresh milk into a dirty glass.

WHAT CAN YOU LEARN BY EXAMINING A USED FILTER?

A used oil filter can tell a story, and inspecting an oil filter after use can help identify potential engine problems.

If you remove a filter that appears ballooned, bulged or deformed, this indicates it was subject to too much oil pressure, and the oil pressure regulating valve located in the oil pump should be serviced immediately. This valve regulates the oil pressure in the engine. If the valve is closed, restricted or sticks, excessive oil pressure will cause filter deformation and possibly cause the lubricating system to lose all its oil, resulting in engine damage.

When the filtering media is coated with sludge, the sludge could be caused by excessive combustion blow-by gases contaminating the oil. It might also be due to the engine operating temperature being too low, excessive idling, or most likely, an extended oil change interval. Any of these problems should be corrected as soon as possible.

With glycol coolant contamination, the media may be coated with water, and the media pleats will be wavy in appearance from the engine coolant entering the oil. The engine problem must be corrected immediately. Extreme engine wear causes excessive fuel dilution of the oil and possible separation of the media where the contaminants have been flushed out and adhesives are attacked. If you see these warning signs, correct the fuel system problem.

When oxidation occurs, the media may have a brittle and reddish appearance. Oxidation occurs faster when there is excessively high engine temperature or wrong oil viscosity, and the oil may have a strong burned odor. In this case, use proper viscosity oil and/or correct and avoid overheating the engine.

If the filter has collapsed internally, there has been excessive media restriction with possible engine damage due to lack of proper filter maintenance. You should inspect the engine for damage and make certain the driver changes the oil filter at every oil change.

If you find excessive metal particles in the used filter, you should perform an oil analysis or disassemble and inspect the engine components to help determine what components are failing and causing excessive engine wear.

By performing preventive maintenance such as changing the oil and filter, a vehicle's engine life can be extended. Remember, however, if a filter is suspected to be involved in engine damage, it's probably best not to tamper with or destroy the filter. It may be best to return it to the filter manufacturer for testing and inspection.

HOW SHOULD I DISPOSE OF A USED FILTER?

The EPA now requires that used oil filters be hot drained by any of the following methods:

• Puncturing the filter dome or anti-drain valve and hot draining
• Hot draining the filter and crushing
• Dismantling and hot draining

Any other equivalent method of hot draining the filter is acceptable so long as it achieves maximum removal of free-flowing oil.

The EPA recommends that punctured or pierced filters be hot drained for a minimum of 12 hours to adequately remove the used oil in them. A few states have additional requirements for used oil filters, which may include a ban from disposing of used oil filters in the trash or a landfill.

The Filter Manufacturers Council (FMC), a trade organization representing filter manufacturers, has developed a database that is now available as an information source for filter industry customers, installers and independent garages. You can reach the FMC database by calling their filter hotline at 1-800-993-4583.

There is a great deal of technology in today's automobiles, right down to their oil filters. Filter design has come a long way since the time when a filter resembled a roll of toilet paper. I hope this information helps answer some of your questions about this vital engine part.

Pete Sullivan is a technician and owner of Sullivan's Advanced Auto Care in Houston, Texas. He is a triple master certified by the National Institute of Automotive Service Excellence (ASE). He holds a B.S. degree in Physics and Chemistry.