How Often Should You Replace Air Filters & Oil Filters?


While a car or truck engine may seem like a dirty place, dirt is actually one of the worst enemies of engine longevity. For this reason, engineers have designed engines with air and oil filters to keep grime to a minimum. This article will describe the important role of air and oil filters in modern passenger automobiles as well as general guidelines for replacing them.

– Air Filters

For an internal combustion engine to operate two fuels must be present: gasoline or diesel and oxygen. From a molecular point of view, fire is the chemical bonding of any combustible substance and oxygen which results in heat, light and physical energy. Engines take advantage of the physical energy caused by fuel/oxygen explosions to drive a car’s wheels. Air filters ensure that engines will only suck in and use clean air for the combustion reaction.

Clean air is important in the sensitive engine cylinders and valve system. Because dirt and grime can contain gritty substances like sand and other particulates, dirt in your engine can cause scuffs and scratches on important engine parts. Valves are particularly vulnerable – valves are small parts which regulate the inflow of fuel and air and the outflow of exhaust. Because these parts are machined with so much precision, grime and dirt buildups can be dangerous and cause expensive repairs.

To avoid these problems, replace your air filter at least every 25,000 miles or annually, whichever comes first. It is wise to replace your filter even sooner if your vehicle operates in dusty or dirty environments such as on the farm or on the job. For more description, read your air filter or vehicle manual.

– Oil filters

The oil present in engine crankcases serves two purposes. Most obviously it lubricates the moving metallic parts in the engine, thereby reducing friction and the heat and destructive properties associated with it. Second, engine oil contains detergents and additives which clean the crankcase and condition crankcase seals to prevent leakage. Like every high school dishwasher knows, if you try to wash dishes in dirty water you will be fighting a losing battle. The same is true of engine oil – if your oil is dirty or contains a lot of sludge, it cannot properly clean the crankcase of carbon deposits from all those miniature controlled explosions which drive your car. The best step to revitalize the ability of oil to clean your engine is to change it, and with every change of oil there should be an oil filter change as well.

Oil filters are cylindrical objects which (usually) easily screw into the engine block. The only tools required to change a filter are a catch-pan for the oil and sometimes a filter wrench for the particularly hard to remove filters. Here’s a special tip – to avoid a hard-to-remove filter situation, coat the new filter gasket in a thin layer of old engine oil; don’t worry, it won’t leak. If your oil filter is full of engine gunk or dirt, you will know it. There is a marked different in weight between a new and full, used filter, and you can feel it when you hold them. While it is true that the oil filter contains a lot of oil that increases its weight, there is always a substance that doesn’t seem to flow out not matter how long you drain the old filter – that’s the gunk.

Oil filter changes should be performed with each scheduled oil change, normally 3,000 miles or three months, whichever comes first. Engines which perform mainly highway driving and don’t drive in severe conditions can usually get away with 7,500 miles on a good filter. Cars and trucks which drive in severe climates or under high stress environments should change the filter and oil at least every 3,000 miles, even sooner if the situation dictates. Remember, check your oil filter and/or vehicle manual for more detailed answers.

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