Choosing an Oil Filter

Oil Filters 101

Story Kevin Haper Images Royal Purple - September 23, 2011 12:00 PM


Magnified view of the filter media inside the unit. This will keep you from cutting up your own filter to see what’s inside.


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It’s one of the unsung heroes found on or in your car’s engine. It has a clear purpose that’s understood, but the level of understanding goes beyond the “what does it do?” question. The informed consumer and car lover needs to know how it does what it does and why. Otherwise, you could make some buying decisions that may unintentionally lead to problems down the road.

On the surface, the typical oil filter doesn’t look like much, but it was never designed to be a style point in a judging competition. It was designed to be functional and fit where it needed to go. It is a place where size matters, and that’s more than just looks.

In today’s economy, it’s more important than ever to take care of your vehicle, and the smallest elements can make the biggest differences. The engine maintenance program adds life, no question about it. So for those who want their vehicle to last, it’s high on the list.

There’s plenty of talk about oil, its composition, its uses, the grades, the drain intervals, etc. When you consider an oil change, you are keenly aware of the type of oil you want in your car. Of course, an oil change involves a filter change. Here’s where the decision-making process starts to venture off. You may choose the correct size, but then you see an array of brightly colored products that will fit the bill. You start to see your thinking become diluted. You’re in a hurry; you want to get it done. You decide any of these will do. You decide it is not really that important.

Oh, but it is.

That oil filter that you picked up is going to be responsible for getting the maximum life and protection in concert with that oil that you have agonized over. The filter has to have the capability of flowing high volumes with relatively low restriction. Do you know the right choice? Do you know the differences? Can you see past the marketing or the colors to get the right one?

We turned to Royal Purple. They have come into the filter market after years as strictly a lubricant brand. Do you think it was an afterthought? On the contrary, they came to market only when they had a product that had the efficiency that would meet or exceed the standards used by others.

The best place to start is with an understanding of the components of an oil filter. Each has a critical role in the function of the piece. While only some may be directly related to the filtration side of things, there is a clear need for the functions involved in protecting the filter itself from damage.

Components of an Oil Filter

Shell: The shell of the oil filter is the outside casing that you actually see when the filter is installed. The shell is responsible for keeping your filter safe during all of the wear and tear your vehicle goes through. It offers protection from puncture wounds that could create leakage. The typical spin-on oil filter is usually constructed of steel.

Media: The media (plural of medium) is the actual filtering component inside the shell. Depending upon the level of filter you have chosen, the media can be described as a maze of cellulose (wood pulp with a small percentage coming from cotton linters pulp and grasses), synthetics and/or microfibers that form the medium which removes the harmful debris from your engine oil.

Anti-Drainback Valve: This is something that may not be found on all filters. For the ones that do employ it, there’s a critical function to consider. The anti-drainback valve prevents oil drainage from the filter during engine shutdown. It is important to keep oil inside the filter even during engine shutdown. This prevents the “dry engine start-up” scenario, which helps reduce engine wear.

Core: The core is the part of the filter that helps keep the filter in its proper shape and prevent collapsing under extreme pressure. It is inserted inside of the filter media and can be made of a variety of materials.

Baseplate: The baseplate is the threaded component of the oil filter. It has an additional role of directing the inlet and outlet flow of the oil in the filter. The steel thickness and plate geometry (its shape) are the main factors in the structural strength of the filter.

Gasket: The gasket is the rubber ring that seals the filter to the engine’s oil filter base location. The gasket is typically made of flexible rubber. However, components can vary in material by company preference. A substandard material can not only affect sealing capability but also the ease of installing/removing the filter itself.


The Right Choice

As you might expect, not all oil filters are made the same. While you can usually tell the difference by the price point, there are still some factors to watch for and some cues an informed car enthusiast can utilize.

Good: Most entry level “economy” filters are very basic in nature, lasting for a more limited time than higher end filters. These filters use media typically composed of natural wood fibers (called cellulosic fibers) used to sort out the debris in your oil. Natural wood fibers are irregular in size and shape. This can have an effect on the filter’s performance at high-flow rates, and generally they have a poor resistance to high oil temperatures. In addition to the media being different, the structural components (baseplate and shell) are of minimal thickness. Since most filters look about the same from the outside, the easiest way to spot a filter of this type is the price and how easily the shell flexes when you squeeze it. These filters likely do not utilize an anti-drainback valve.

Better: This level of filter contains media that is a blend of fibers. The majority of the fibers are cellulose with a minimal blend of synthetic fibers that enhance the media strength and efficiency of performance. The anti-drainback valve is sometimes made from a silicone material which performs well under hot oil conditions. The structural components are usually a little stronger and won’t crush or flex as easily when they are squeezed. These types of filters are designed to extend service intervals.

Best: The premium level of filters uses micro-glass filter technology. These high-tech oil filters use special synthetic glass microfibers that are about 10 times smaller than conventional cellulose filter fibers to provide superior filtration without compromising oil flow. Advanced micro-glass oil filters are designed to extend the life of the vehicle and equipment. In addition to superior filtration media, the other internal and structural components are of higher quality materials, plus construction is better, making for easier installation and removal since they are less prone to crush. In addition, premium filters are designed to far exceed OEM structural requirements and have high internal capacity with optimized flow characteristics for maximum performance and filter life.

Vehicles still under warranty should follow the vehicle manufacturer’s recommended filter change intervals. Most filters are fully compatible with all synthetic and conventional oils. Royal Purple recommends using the high-performance Royal Purple products which have a 12,000-mile life similar to the filter.