Car Air Filter Guide

Engine air filters are mounted in the air intake system for catching dirt and other particles that could damage internal engine parts. They’re mostly made of paper (some are made of cotton or other materials) and should be replaced according to your manufacturer’s maintenance schedule. A dirty or clogged air filter will stop air going into the engine, which in turn restricts the amount of fuel injected. The EPA says the main result is due to a loss of acceleration, with minimal impact on fuel economy.

Most of the modern cars also have a cabin air filter that catches dirt, debris and some allergens in the air that goes through the heating, ventilation and air-conditioning systems. Cabin air filters also require periodic changing, sometimes more frequently than engine air filters.

What is the Purpose of a Car Air Filter?

All cars have air filters, which are important adjunct to proper engine operation. What follows is a brief description of the most basic goals of a car air filter.

Filter Outside Air

The main aim of an automotive air filter is to filter and clean outside air before it gets sucked into a car engine and burned along with fuel to produce combustion.

Protect Vehicle Engine

Air that gets sucked into a car engine has to be as clean as possible to prevent engine contamination and, in some cases, engine damage. An air filter is the main line of defence against stopping the damage particulate matter from entering a vehicle’s engine. Dirty air can decrease engine efficiency and cause damage; an air filter prevents this.

Protect Carburetor/Fuel Injection System

A carburetor or fuel injection system injects both gas and air into an engine’s cylinders, a combination more commonly referred to as an engine’s air/fuel mixture. Both carburetors as well as fuel injection systems use tiny portals and valves to function. Any kind of debris or obstruction that enters these portals and valves can cause serious malfunction and/or damage. An engine air filter helps to protect these delicate parts by filtering incoming air before it enters a carburetor or fuel injection system.

Increase Fuel Economy

A clean, properly installed and functioning air filter increases both engine performance as well as the gas mileage. By filtering incoming air into an engine, an air filter makes sure that air burned inside of an engine is as clean as possible. Clean and purified air ignites quicker and better inside of an engine cylinder, an occurrence that increases engine combustion efficiency, which helps to increase the fuel economy.

Augment Carburetor/Fuel Injection Function

As air gets sucked into a car’s engine, it must first pass across the air filter before it reaches either the carburetor or fuel injection system, which is in charge of combining incoming air with gasoline, a combination that creates an engine’s air/fuel mixture. A dirty air filter stops the air flow and limits the amount of air that reaches the carburetor or fuel injection system, either of which responds by reducing the amount of gas injected into the air. A clean air filter increases carburetor/fuel injection function by maintaining an adequate amount of air flow.

Common Signs of a Dirty Air Filter

A car air filter cleans the air which is entering the engine. Signs of a dirty air filter has a misfiring engine, unusual noises, and reduced fuel economy.

A car engine combines air and gasoline in the combustion chamber for creating power. This air reaches the engine by an air filter that works to keep out road debris, dirt, bugs, and other contaminants that can damage the engine. At the same time, the air filter needs to allow enough air to reach the engine so that it can perform effectively. Over time, the air filter can become dirty and clogged, and the lack of air can also affect the overall performance of your car.

Most auto companies advice that you change the air filter every 10,000 to 15,000 miles, or every 12 months. However, if you typically drive in dusty or rural areas like Scottsdale, Arizona, or San Antonio, Texas, you might want to have your mechanic check and change it quite frequently, such as every 6,000 miles. Driving in crowded areas where there is heavy traffic – like in Los Angeles and Washington D.C. where you have to stop and start more often also requires you to replace the air filter more frequently.

Make note of these symptoms that show your air filter needs replacing:

Reduced fuel economy

Your engine compensates for lower amounts of oxygen through consuming more fuel to produce sufficient power. Thus, if you find that your fuel economy is going down, it could be an indication that the air filter needs replacing. However, this is true for carbureted cars only, most of which were made before 1980. Newer cars with fuel-injected engines have on board computers which help to calculate the amount of air taken into the engine, and adjusts the fuel flow accordingly. Therefore, the cleanliness of the air filter on newer cars shouldn’t significantly have an effect on the fuel economy.

Misfiring engine

Restricted air supply from a dirty air filter leads to unburnt fuel exiting the engine in the form of soot residue. This soot accumulates on the spark plug, which in turn cannot deliver the required spark to combust the air-fuel mixture. You’ll find that the engine does not start up easily, misfires, or jerks roughly.

Unusual engine sounds

In normal situations, when your car is stationary with the engine turned on, you should sense the smooth rotation of the engine in the form of subtle vibrations. If you notice your car vibrating excessively or hear a coughing or popping sound, it is often because of a dirty or damaged spark plug resulting from a clogged air filter.

Check Engine Light comes on

A lot of modern engines suck up about 10,000 gallons of air for every single gallon of fuel burned in the combustion cycle. Inadequate air supply can lead to carbon deposits accumulating in the engine which may set off the Check Engine Light. If that takes place, have your mechanic check the air filter among other diagnostics.

Air filter appears dirty

A clean air filter appears white or off white in colour, but as it start to accumulate dust and dirt, it will look darker in colour. However, quite often, the inner layers of filter paper inside the air filter might have dust and debris that is not visible even in bright light. Therefore, it is important that you have your mechanic check the air filter when you take the car for maintenance. Ensure to follow the manufacturer’s instructions regarding replacement.

Reduced horsepower

If your car does not respond properly or if you notice jerking movements when you press the accelerator, this could show that your engine is not receiving all the air it needs to perform. Replacing your air filter can help to improve acceleration or horsepower by up to 11%.

Black sooty smoke or flames exiting the exhaust

An inadequate air supply can lead to some of the fuel not burning completely in the combustion cycle. This unburnt fuel then exits the car across the exhaust pipe. If you see black smoke coming from your exhaust pipe, have your mechanic to replace or just clean the air filter. You might also hear popping sounds or even see a flame at the end of the exhaust. This takes place when the heat in the exhaust system ignites unburnt fuel near the tailpipe. This is a potentially hazardous condition and needs to be diagnosed right away.

Smell of gasoline when starting the car

If there isn’t adequate oxygen entering the carburetor or fuel ejection system when you start the car, the excess unburnt fuel exits the car through the exhaust pipe. That’s when you’ll smell the gasoline and know that it’s time for replacing the air filter.


On most modern vehicles, the air filter is under the hood inside a rectangular cold air collector box that’s found near the front of the engine compartment. (Other vehicles, having those with carburetors, have big round metal air cleaners that are hard to miss.)

The air cleaner has a large air inlet duct (also called the air intake hose) which is connected to it. Loosen the hose clamp that seals it to the box, and then undo all the screws, clamps, or wing nuts that hold the lid of the box in place. Put the fasteners that you removed somewhere safe so that they don’t roll off into oblivion. Open the lid of the box and you will find the air filter inside (as shown here). Lift out the old filter (it isn’t fastened down) and take a look at it.

Some older vehicles have permanent air filters, and some off-road vehicles have more-complex filters with wet and dry elements. Clean and replace these according to the instructions present in your owner’s manual.

To figure out whether your air filter has to be replaced or not, just hold it up to the sun or to a strong light. You should see the light streaming through it? If not, try dropping it lightly and bottom side down, on a hard surface. Doing so should jar some of the dirt loose. If the filter is still too dirty to see through after you’ve dropped it a few times and it looks like it just needs a bit of cleaning, you can try to clean it. If that doesn’t work, you have a new one.

To clean a pleated air filter use either an air hose to blow the dirt off (not through) it or a vacuum for sucking it out. For both methods, handle the filter gently for avoiding crushing the pleats. Keep the nozzle of the air hose or vacuum cleaner several inches away from the filter and make sure you don’t jam it up against it. And if you’re using compressed air, do it away from the vehicle in order to avoid blowing the dirt around under the hood.

If the interior of the box is fouled with dust or sand, before you clean the box, just paste some duct tape over the open end of the air intake hose so that the dirt can’t get in. After that, either use the compressed air hose to blow the dirt out of the box or the vacuum cleaner to suck it out.

When the cleaned filter or the new filter is in place, put the lid back on the box and replace all the stuff that held it on. Finally, remove the duct tape from the open end of the air intake hose and use the hose clamp to reattach it to the box and it’s done.

Video of Tips for Replacing a Car Air Filter

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