Filter Facts

AAA Auto Repair Article
By AAA Automotive
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If you’re a long-time vehicle owner, you’ve likely replaced your fair share of filters, but how many of them were necessary? Thanks to advances in technology, today’s cars and trucks can go much longer between filter replacements compared to older automobiles.

(Image: AAA)
Engine Air Filters

In older carbureted engines, a restricted air filter could have a significant impact on fuel economy, and some service providers still claim this is still true with modern fuel-injected vehicles. Wrong. Today’s fuel injection systems automatically compensate for the amount of available air and adjust fuel flow accordingly. While a dirty air filter can diminish your engine’s power output, it won’t have any effect on how many miles you get per gallon of gasoline.

A good practice is to have the engine air filter inspected at every service interval, and replace it only when necessary. While some trucks have an air filter monitoring devices that measures the amount of pressure drop across the filter with the engine running, most air filters are inspected visually. The technician will place a light behind the filter and look to see if any illumination shines through. If less than half of the filter’s material passes light, it’s time for a replacement. It is worth noting that some newer filters use dense materials that won’t transmit light, even when brand new. In this case, simply follow the manufacturer’s mileage recommendation for how often to replace the filter.


Fuel Filter

Thanks to improved refining processes and environmental standards, today’s automotive gasoline is cleaner when it comes from the pump and cleaner when it burns in the engine. In the past, impurities in gasoline would clog fuel filters, which meant they required regular replacement. Clean modern gasoline and the high-capacity filters used with fuel injection have pretty much eliminated the need for periodic replacement. Today, fuel filters are generally only changed on high-mileage automobiles as part of a larger cleanup of a contaminated fuel system.

While gasoline engine fuel filters don’t require much attention, diesel engine fuel filters require vigilant monitoring. Diesel fuel is less refined than gasoline, so it’s common for it to contain more particulates that can clog the filter, which means periodic replacement is necessary. Because water contamination of the fuel can ruin a diesel fuel injection system, most diesel fuel filter assemblies incorporate a water separator that must be drained at regular intervals. Left in the system, water creates a breeding ground for fungus, bacteria and other biological agents that cause fuel system damage.


Cabin Air Filters

If you suffer from allergies or other respiratory conditions, you understand the importance of clean air. As your car travels down the road, outside air circulates through the heating, ventilation and air conditioning system. Unfortunately, that air brings with it a number of impurities such as:

• Pollen
• Brake dust
• Soot
• Insects
• Exhaust particulates

Instead of forcing you to breathe these materials, many manufacturers install cabin air filters to create a more pleasant interior environment. These range in sophistication from simple single-stage filters to advanced multi-layer designs that sometimes use activated charcoal to eliminate unpleasant odors.

While these filters work hard to produce high-quality cabin air, you’ll only reap the benefits if you follow the manufacturer’s recommended replacement intervals. Your owner’s manual has a maintenance schedule, but you might want to replace the cabin filter more often if you drive in heavily-polluted areas, on gravel roads or live in a region that regularly experiences dust storms or wildfires.


Ensure Proper Flow

No matter if you’re talking about air, fuel or cabin filters, cars and trucks rely on a steady flow of liquids and gasses for normal operation. Filters help ensure that unwanted materials are kept out of sensitive areas. If you’re starting to notice a drop in performance while out on the road, the culprit could be a clogged air or fuel filter. If airflow through your heating, ventilation and air condition system seems restricted, a new cabin filter may be in order. If you’re looking for a high-quality repair shop to handle this important work, AAA has a list of local Approved Auto Repair facilities that meet a strict set of association standards.
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