What is an Oil Filter?

OEM Briggs and Stratton Oil Filter


What in the world is that? It’s a Small Engine Oil Filter.

Ok. So real quick, there  might be a little canister looking thing that screws into the side of your engine. Might be black, might be yellow, might be white…who knows? We’ll narrow that down later. But, if it looks anything like the picture above, then you have an oil filter. Congrats!

The oil filter is a pretty simple device and the purpose of the oil filter is to…you guessed it- filter oil.

There are several components to the Oil Filter. You will probably never see most of them unless you take a band saw and cut one in half. But since you’re reading about the Oil Filter, I guess I kind of owe it to you to tell you about them. So here we go!

At the bottom of the filter is a thing they call the “Tapping Plate”. You’ll know it by the threaded center hole. That is where the filter attaches to the engine. There’s also a ring of holes around the outer edge. Those allow oil to flow back into the engine once its been filtered.

The center hole is actually the opening for the Center Steel Tube. This tube is riddled with holes, which allow the oil to pass through.

Up inside the center hole is a rubber valve called the “Anti-drainback valve”. It keeps the oil that enters the center hole from just draining back into the engine.

The actual filter material inside of the Oil Filter is called the “Filter Medium”. If you look at an average home furnace filter, its pretty similar. It is made mostly of organic and inorganic fibers like cellulose, polyester and glass. The purpose of these fibers is to give any contaminates a place to grab onto. The Filter Medium is folded in accordion shape. Why? More surface area for the debris to get stuck to.

If the oil is too thick (due to cold) to flow freely through the filter, there is a Relief Valve that will open when enough pressure builds up. Although the oil passing through the relief valve is unfiltered, it will begin the process of oil flow. Once the oil warms up, the relief valve will close and the oil filter will begin normal operations.

What you need to know is that from time to time you will need to replace your oil filter with a new one. (We’ve got them all!!!!) The good folks at Briggs and Stratton recommend that you check your oil regularly for both quantity and quality. Fresh oil is amber in color. Black oil is dirty and should be replaced.

“Manufacturers recommend changing the oil in your small engine after every 25 hours of operation. For a new engine, you’ll also need to change the oil after the first five hours of operation. New engines require this extra step to flush out small particles that accumulate naturally during the break-in period.” 


So, the majestic oil filter laid bare! Time to slide along to the next one.


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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.