Rick's Free Auto Repair Advice

How to check your car’s air filter

How to visually check your car’s air filter

Most carmakers list a mileage for air filter life. But the mileage is based on normal driving conditions. Regardless of the mileage, you should check your car’s air filter every time you change your oil. If you drive in a sandy/dusty area or commute in an area with smog, check your engine air filter more often.

How to visually check you air filter

• Remove the filter from the filter box
• Separate the pleats and check for a buildup of debris at the bottom of the pleats. Replace if you see a noticeable amount of debris dirty engine air filter
• Look for signs of oil contamination.  They’ll be darker than the rest of the filter. If the oil-soaked areas account for more the 25% of the filter, replace it.
• Most air filters have a foam or rubber gasket around the edges. If you see bits of the filter are falling off or the rubber seal is deformed or cracked, replace it.

Oil stains on the air filter media

An engine’s positive crankcase ventilation (PCV) system is designed to suck blow-by gasses out of the engine and into the intake manifold where they’re burned. The replacement ventilation air is filtered by the oil soaked air filterengine air filter. If the PCV system isn’t working properly or the engine is worn to the point where it’s producing too much blow-by, crankcase pressure can push oil laden blow-by backwards into the air filter.

Oil stains on the engine air filter indicate a PCV or piston ring problem that should be addressed. However, in the meantime, the oil stain on the engine air filter is restricting airflow and the filter should be replaced.

Check for pleat deformation

An engine air filter that’s ‘sucked in’ is an deformed engine air filterindication of a problem. If it’s a new filter, the sucked in condition means the filter is overly restrictive and does not meet the carmaker’s specifications. If it’s an older filter, the sucked in condition means it’s clogged can can’t pass enough air through to satisfy engine conditions. Replace any filter that’s deformed or ‘sucked in.’

Avoid these engine air filter inspection myths

Myth #1: You can check the condition of an engine air filter by passing a light behind the pleats to see how much light comes through.

There is no scientific proof that this test proves the condition of the air filter. Some filters that appear black and don’t pass much light perform perfectly well in laboratory testing. Light passage is not a way to check an engine air filter.

Myth #2: A discolored or dirty looking filter means it should be replaced

Aside from seeing debris filing up inside the pleats, there is no valid visual inspection to determine an engine air filter’s condition. In other words, there is no scientific correlation between a filter’s color and its condition.

Myth #3 You can use compressed air to blow out particles and rejuvenate an old air filter

You may think you’re extending the life of your air filter by blowing dirt out of it with compressed air. But what you’re really doing is damaging the filter. The air pressure doesn’t just blow the dirt out; it actually enlarges the pores of the filter. From that point on, the filter will let in more dirt and cause more engine wear.

© 2023 Rick Muscoplat

Posted on by Rick Muscoplat



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