All About Oil Filters

Changing your vehicle's oil and oil filter is a ritual for many DIYers — I get giddy just thinking about it. But what do you really know about that oil filter, besides how much it cost and what the ads tell you?

To help you choose the best model for your vehicle, here's a look at how filters are built, what we want from them, and what's new on the street.

Oil filter anatomy
In a nutshell, an oil filter is a steel canister containing a filter medium and an anti-drainback valve that keeps the oil in the filter from draining out after the engine is turned off. Some manufacturers use rubber, which does not remain flexible under extreme temperatures; others use silicone, which stays flexible and will not break down under extreme heat.

The heart of the oil filter is the filter medium, pleated and wrapped around a center tube through which the oil flows. Some tubes are straight; some are spirals. (According to manufacturers, the spiral helps to decrease drag on the oil as it flows through the filter, especially on cold starts.) The filter media itself can be traditional paper or cellulose (usually found in low-end filters), a combination of cellulose and synthetic material such as fiberglass, or a synthetic medium (usually used in better, high-performance filters). All filter media are designed to hold contaminant particles larger than 20 microns (a human hair has a diameter of about 70 microns); the better the medium, the smaller the particles captured and the greater the dirt-holding capacity and longevity of the filter.

The filter element itself is held in place within the filter body by end caps, and a coiled metal spring between the top of the filter element and the housing ensures a constant load on the inner element, even during pressure surges.

The last essential element in an oil filter is the safety bypass valve, which allows oil to bypass the filter in cold temperatures, under high pressure or when the filter medium has become too dirty to allow enough oil through to meet the demands of the engine — in situations like that, it's better to have dirty oil flowing through the engine than no oil at all.

What to buy
Many manufacturers and distributors market oil filters based on their performance capabilities. For example, NAPA's Silver Series filters have a cellulose medium, its Gold Series filters are made with a hybrid cellulose-synthetic medium, and its Platinum Series filters have a fully synthetic medium. Prices increase from silver to gold to platinum, a do filtering ability and longevity (photo, below).

NAPA's oil filters are marketed as Silver, Gold and Platinum series, which escalate in price and performance.

One interesting development in oil filters is the MicroGreen filter by Soms Technologies (photo, below). Similar to other filters in appearance and in its installation method, the MicroGreen filter utilizes a second filter element that can trap particles as small as 2 microns. According to the manufacturer, using the MicroGreen filter allows you to drive a vehicle under normal conditions up to 10,000 miles before changing the oil filter and up to 30,000 miles before changing the oil.

The MicroGreen filter uses a secondary filter element to remove particles as small as 2 microns from the oil.

Besides aiding convenience, this helps the environment because it conserves oil and filters (only about half of which are properly recycled, according to the Environmental Protection Agency). The manufacturer says MicoGreen filters can substantially reduce the use of raw materials and the production of hazardous waste and CO2 emissions (due to decreased oil need, resulting in decreased oil production and filter manufacturing). Though the filters are not cheap (a pack of two costs $35), the savings to your wallet and the environment may be significant.

Another product worth mentioning is the FilterMag, a magnetic sheet that you wrap around the oil filter. According to the manufacturer, powerful magnets trap steel particles as small as 2 microns against the inside of the filter's steel can, preventing them from re-entering the engine and causing damage. The oil-analysis test on the manufacturer's Web site shows a huge decrease in iron-particle count in used filters when the FilterMag was installed. Prices range from $50 to $115.

No matter what filter you choose, ask about its micronfiltering rating and anticipated service life before you buy. If you're running synthetic oil, choose a filter that's specifically engineered for it. Most important, adhere to your vehicle's service requirements. No matter how well the filter performs, it can't do its job if you neglect to change it.

The FilterMag is installed around the oil filter and captures metallic debris before it has a chance to re-enter the engine via the oil flow.

Changing Your Own Oil
Changing your own oil and oil filter is an easy way to save money, and it gives you a good reason to get under the hood and tinker with vehicles. But we all need to be responsible about the waste involved. One gallon of oil can pollute 1 million gallons of water, so it is essential to dispose of used oil and filters properly. Bring the contaminated oil and filters to a gas station, an auto-parts store or a hazardous-waste collection facility. These places often accept the materials at no charge, but even if you must pay a fee, it's worth the investment to help keep the planet clean.