Filters are the first line of defense against contaminants, whether it is air-borne contaminants entering the engine, wear particle, dirt or soot contaminants inside the engine, wear or dirt particles inside the transmission, or dirt or rust particles in the fuel. Many late-model cars and trucks also have cabin air filters to stop unwanted contaminants such as dirt, soot, pollen, odors and even bacteria entering the passenger compartment.
Filters don’t last forever, so they have to be replaced periodically according to the vehicle manufacturer’s recommended service intervals — unless they are a so-called “lifetime” filter (such as a fuel filter inside the fuel tank or a transmission filter) that has no factory recommended replacement interval. In the case of the latter, replacement is usually recommended when related repairs or service is performed (such as replacing the fuel pump assembly or changing the transmission fluid).
The most often replaced filter is the oil filter. It usually gets changed every 3,000 to 7,500 miles on most vehicles (unless the vehicle owner is neglecting normal oil changes). On many late-model vehicles, oil change intervals have been extended from the traditional 3,000 miles or 6 months, to 5000 to 7500 miles or more, or once a year. With the longer service intervals, it’s even more important that the oil filter be replaced with every oil change (some people change the filter every other oil change to save money).
Premium long-life filters are recommended for applications that have extended oil change intervals. Most of these filters use some type of synthetic filter media instead of cellulose. A growing number of late-model engines are also being equipped with cartridge style oil filters rather than spin-on filters. One difference here is that the filter cap o-ring also needs to be replaced when the filter is changed. A new o-ring is usually included in the box with the filter.
Air filters are another frequently replaced maintenance part, especially in rural areas where dusty gravel roads can clog a filter very quickly. The normal factory recommendations to replace the filter every 30,000 to 50,000 miles obviously don’t apply here. For most vehicles, the air filter should be inspected at every oil change, and replaced every 12 to 24 months, or every 12,000 to 24,000 miles depending on how dirty it is.
The most overlooked filter on most vehicles today is the cabin air filter. Many motorists don’t even know their vehicle has one, let alone where it is located or how to replace it.
Cabin air filters come in two basic varieties: pleated paper dust filters and combination dust/odor filters. The combo filters usually have a layer of activated charcoal to trap odors. The carbon reacts with odors and other airborne pollutants to neutralize them before they enter the passenger compartment. They can even reduce the levels of carbon monoxide and oxides of nitrogen from the exhaust of other vehicles.
Some cabin air filters are also treated with a chemical biocide or a special surface treatment that destroys bacteria, fungus and mold spores on contact. This is important to prevent the growth of unwanted organisms and odors.
If a cabin air filter is not changed, eventually it will plug up and restrict airflow into the HVAC system. This can reduce airflow from the heater and defrosters in cold weather, and cool air from the A/C ducts during hot weather.
Combo filters are shorter lived than dust filters, and should be replaced yearly or every 12,000 to 15,000 miles to maintain their odor-absorbing abilities. Dust filters can go longer, up to 20,000 to 30,000 miles or more. But they should be inspected yearly to see if they’ve become clogged with dust or debris. Cabin air filters are usually located either in the plenum area at the base of the windshield, or in the HVAC air inlet under or behind the glove box inside the passenger compartment. The location can be found in the vehicle owner’s manual, or in a filter location guide. In some cases, there may be a slot or other provision for a cabin air filter, but no factory-installed filter. Also, on some applications (such as certain Chevy trucks and SUVs), some years and models have cabin air filters while others do not. If there is no cabin air filter listed for a given year, make and model of vehicle, it probably doesn’t have one.
Finally, what about filter upgrades? Standard replacement filters should be adequate and meet all OEM requirements. However, many filter suppliers also offer premium replacement filters that may have one or more special features such as longer filter life, higher filtration efficiency and/or more rugged construction (such as a metal tube inside an oil filter instead of a plastic or cardboard tube). Premium filters can be recommended to customers who may need extra filtration protection because of the way they drive their vehicle or where they drive it.