Common Signs of a Dirty Air Filter | Autance

To generate power, a car engine combines both air and gasoline. The former gets to the engine through an air…

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Common Signs of a Dirty Air Filter | Autance © Common Signs of a Dirty Air Filter | Autance

To generate power, a car engine combines both air and gasoline. The former gets to the engine through an air filter which is designed to keep out a host of debris including dirt, bugs, pollen, and other harmful contaminants. After it has been in use for a while, it will not function as effectively as it once did. And when this happens, less air will reach the engine, which can lead to extensive car trouble further down the line. As a rule of thumb, it is recommended that you change the filter every 10,000 to 15,000 miles.

If you get regular tune-ups at your local garage, many mechanics will automatically check if the filter to see if it needs replacing or not. However, you don’t want to only rely on others. It is important that you are able to identify some common warning signs yourself. Otherwise, you could end up causing further damage to your vehicle which was easily avoidable.

The question remains: how can you tell if your air filter is dirty? Well, we are going to help you answer this query by talking you through some of the most common signs that it is time for a replacement filter. So, here are the top 10 indicators that you need to take action on your air filter.

Air Filter Appears Dirty

The most obvious way to tell if an air filter is dirty is to check to see if it looks dirty! While this may seem obvious, a lot of car owners don’t think about undertaking this task. Brand new filters are clean and nearly white in color, while older ones will turn brown or black due to the contaminants in the air. When you are examining your filter, you need to make sure that the light source that you are using is sufficient. So, you should either do the check during the daylight hours or else use a flashlight to illuminate the area. Signs of dust, dirt, and debris could be an indication that it is time for a change, but you may want to check some of the following issues too.

Reduced Fuel Economy

When your engine is receiving less oxygen, it will have to consume more fuel to produce enough power. If you notice that you are not getting as many miles to the gallon as you once did, this could be a sign that it is time to replace the air filter. However, this generally only applies to older cars as newer ones have fuel-injected engines with onboard computers. These determine the amount of air taken into the engine and adjust the fuel flow as required. So, reduced fuel economy due to a dirty air filter only tends to be an issue associated with older vehicles. But if this issue is occurring, it is one that you will want to tackle as soon as possible. Nobody likes having to visit the gas station more often than they have to!

Misfiring Engine

If you are having a hard time starting your car or you need to excessively rev the engine to get it going, it could have a low air to fuel ratio. When there is too much fuel, this can cause the engine to flood, as well as spark plug pollution. Unburnt fuel will start to exit in the form of soot residue. So, if you find that you are consistently struggling to start your engine, the air filter is the first place to inspect.

Strange Engine Noises

Strange noises emitting from your car are always a worrying sign. When your car is stood stationary with the engine on, it should be purring and producing some subtle vibrations. Of course, the specific engine noises depend on the type of car and how old it is. If you start to notice more vibrations than usual or you hear coughing or popping sounds, this could be due to a dirty spark plug. Listen out for these when your vehicle is stationary. If you are stopped at a traffic light and you hear some coughing and spitting, this is not a good sign. And as we have already mentioned, this is often the result of a clogged air filter.

Bad Spark Plugs

We have just mentioned how the air filter and spark plugs are closely connected parts of your vehicle. A dirty air filter is likely to inhibit the performance of the spark plugs, which ignite the air and fuel mixture inside your vehicle. Check the condition of your spark plugs and air filter to see if either or both are in need of replacement. If you replace both, it is likely that you will notice a marked improvement in the overall performance of your vehicle.

Check Engine Light On

Your check engine light is there for a reason, and it is certainly not something to be ignored if it comes on. One of the most common problems which it shows is deposits in the engine, as these impurities will have an impact on engine performance. Combustion engines can’t function without enough air. In fact, for every gallon of gasoline consumed, thousands of gallons of air are required to process the fuel efficiently. If the check engine light comes on, it is worth having a motor specialist inspect your vehicle as soon as possible to determine what the source of the issue is.

Reduced Horsepower

If your acceleration doesn’t seem quite as powerful as it once did, there is every chance that your horsepower could be suffering as a result of oxygen deprivation. And if your car doesn’t seem to be responding as normal, it may not be getting the air it needs to function. Otherwise, there may be a jerking movement when you put your foot down. If the engine is fighting harder to work with reduced oxygen levels due to a dirty air filter, it will not be operating at peak performance levels. In fact, replacing your old air filter can help to improve your acceleration and horsepower by as much as 11%.

Flames or Black Smoke from Exhaust Pipe

Any black smoke or flames being emitted from your exhaust pipe should raise red flags immediately. If fuel is not being burnt completely in the combustion cycle, it could start exiting the car from the exhaust pipe. A common sign that this is occurring is a popping sound, which occurs as the highly heated fuel is being expelled out of your exhaust system. And flames around your car are never a good sign! Not only does this waste fuel, but this can also end up being very dangerous to your vehicle and the environment. Any unusual exhaust problems need to be diagnosed as soon as possible by a motor specialist.

Strong Fuel Smell

We have already talked about the problem of gasoline being emitted from your exhaust pipe. We all know the smell of gas, and this could be a clear indication that it is time to replace your air filter. Of course, another issue which this could indicate is a fuel tank leakage. If you want to be sure, you can check for the signs of black smoke that we discussed in the previous section. But you shouldn’t continue to drive your car if the smell of gasoline lingers as this is never a good sign.

Rough Idle

Try turning the engine on and simply leaving it idle. Now, check the number of revolutions on your dashboard. It should appear somewhere between 900 and 1,100, which is considered normal for an idle engine. This normal range occurs as air and fuel are mixed together in the combustion chamber. However, if you have a bad air filter, this will cause the air in the chamber to be limited. In turn, this will throw the RPM range out of whack. So, if you notice that the range is much higher or lower than 1,000, there is likely to be a problem which needs addressing. And there is every chance that this is a dirty air filter.


Replacing your air filter when it is dirty is a simple job to do, but it makes such a big difference to the performance of your vehicle. Just a few of the issues which can arise if you don’t tackle this task quickly are an increase in harmful emissions, damaged spark plugs, engine build up, and wasted fuel. All you need to do is keep your filter clean and well-maintained to stop yourself from needing an expensive fix. This can also help to extend the life of your vehicle. The longer you drive a vehicle with a dirty air filter, the more you will be wasting fuel, and the greater the chance that a serious issue will occur. If you don’t think that you can replace the filter by yourself, you will need to visit your local mechanic to get a professional to do the job for you.


  1. How to Clean an Air Filter – wikiHow
  2. How long does a car’s air filter last? – howstuffworks
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