What filters are in the car and why are they needed: a complete guide

A car is a complex system where each element plays an important role. Filters occupy a special place: they protect the engine, transmission and interior from pollution, extending the life of key components. But many drivers don’t even know how many filters are installed in their car and how they affect the car’s performance.

In this article we will analyze in detail all types of filters that are found in modern cars: from the usual oil and air filters to the lesser known fuel and particulate filters. You'll learn where they are located, how they work, and what signs indicate the need for replacement. And also - let's debunk the myths about “eternal” filters and tell you why saving on their maintenance can result in expensive repairs.

The material will be useful both for beginners who are just learning the basics of car ownership, and for experienced drivers who want to systematize their knowledge. We will not go into technical details, but we will give clear practical recommendations that can be applied today.

1. Oil filter: protecting the heart of the car

The oil filter is one of the most critical elements in the engine lubrication system. His task is capture metal shavings, wear debris and other contaminants, which are formed during engine operation. Without it, the oil would quickly turn into an abrasive slurry that would destroy bearings and cylinders.

Most modern cars use full flow filters — they pass through themselves the entire volume of oil circulating in the system. Less common partial-flow, which clean only part of the oil, but more thoroughly. The latter are often installed on diesel engines or premium cars.

• 🔧 Where is: usually at the bottom of the engine, near the sump (sometimes integrated into the oil pump).
• ⚙️ Types of designs: non-separable (disposable), collapsible (with a replaceable filter element).
• ⏳ Service life: coincides with the oil change interval - usually 10,000–15,000 km or once a year.

⚠️ Attention: If the oil pressure light on the dashboard stays on for more than 5-7 seconds after changing the oil, this may indicate a faulty or incorrectly installed filter. Immediately turn off the engine and check the connection for leaks!

When choosing an oil filter, pay attention to:

• 📋 Oil brand compatibility (synthetics, semi-synthetics, mineral water).
• 🔍 Quality of filter material (optimally - cellulose with synthetic fibers).
• 🛡️ Presence of a check valve (prevents oil from draining from the filter when the engine is stopped).

2. Air filter: the lungs of your engine

An internal combustion engine consumes up to 10–15 m³ air - about the same as a person in 2 weeks. The air filter cleans this flow of dust, sand, insects and even small stones that could damage the cylinders and pistons.

Depending on the engine type and operating conditions, filters are divided into:

• 🌿 Paper - the most common, disposable, impregnated to trap small particles.
• 🧹 Inertia-oil — used in old carburetor cars, require periodic washing.
• 🔥 Zero resistance filters (for example, K&N) - reusable, improve dynamics, but require regular maintenance.

Signs of a clogged air filter:

• ⚠️ Increased fuel consumption (up to +10–15%).
• 🐢 Reduced engine power, especially on climbs.
• 🔊 Unusual sound when the engine is running (whistle, wheezing).

Filter type	Service life	Replacement features
Paper standard	15–30 thousand km	Change along with the oil filter or more often when driving on dusty roads
Inertia-oil	50 thousand km	Wash every 10 thousand km with a special composition
Zero resistance	100 thousand km+	Clean and impregnate every 5–10 thousand km

⚠️ Attention: If you have installed a zero resistance filter, never wash it with regular shampoo or gasoline! This destroys the special impregnation. Only use cleaners intended for this purpose (e.g. K&N Cleaner).

3. Fuel filter: barrier to dirt in the gas tank

The fuel filter removes impurities, water and rust from gasoline or diesel that can damage the injectors, pump or the entire fuel system. In modern cars they are often installed two-stage filtration system:

1. Coarse filter — a mesh in the gas tank or on the fuel pump.
2. Fine filter - the main element that captures particles up to size 5–10 microns.

Diesel engines have higher filtration requirements, so they often add:

• 💧 Separators - to separate water from fuel.
• ❄️ Heaters — prevent fuel freezing in the filter in winter.

Where to look for a fuel filter?

• 🚗 Gasoline cars: often built into the fuel pump (in the tank) or under the hood/underbody.
• 🛻 Diesel cars: usually under the hood, near the injection pump, or on the fuel line.

What happens if you don't change the fuel filter?

A clogged filter causes a drop in pressure in the fuel system. The engine begins to “trouble”, loses power, and in critical cases may not start at all. In diesel cars, a dirty filter in winter can cause waxing of the fuel - its crystallization, which completely blocks the supply of diesel fuel to the engine.

Replacement periods depend on the type of fuel and operating conditions:

• ⛽ Gasoline: every 40–60 thousand km (or once every 2-3 years).
• ⚙️ Diesel: every 20–30 thousand km (or before winter).

4. Cabin filter: clean air for driver and passengers

The cabin filter is the only one on the list that directly affects comfort, and not the technical condition of the car. It cleans the air entering the cabin through the ventilation system from:

• 🌫️ Dust and soot (especially important in the city).
• 🌿 Plant pollen (important for allergy sufferers).
• 🚗 Exhaust gases and unpleasant odors (in filters with a carbon layer).

There are two main types of cabin filters:

1. Regular (dusty) - only retains solid particles.
2. Coal - additionally absorb gases and odors (for example, from Mann Filter CU or Bosch Active Carbon).

Where is the cabin filter located?

• 🚗 Standard place: behind the glove compartment (passenger side) or under the hood near the windshield.
• 🔧 Rare options: under the dashboard or at the driver's feet (for example, in some models Volkswagen or Renault).

⚠️ Attention: If, after turning on the stove or air conditioner, a moldy smell appears in the cabin, this is a sure sign that the cabin filter is not only clogged, but has also become a breeding ground for bacteria. In this case it needs to be replaced immediately, and treat the ventilation system with an antiseptic (for example, Liqui Moly Klima-Anlagen-Reiniger).

5. Diesel Particulate Filter (DPF) and Catalyst Filter

These filters are found only in diesel and some gasoline cars with an exhaust gas aftertreatment system. Their task is reduce harmful emissions into the atmosphere, trapping soot and toxic compounds.

Diesel Particulate Filter (DPF) installed on all modern diesel cars (Euro 5 and higher). He delays until 99% soot particles, but over time it becomes clogged and requires:

• 🔥 Passive regeneration — combustion of soot at high temperatures (occurs automatically on the highway).
• ⚙️ Active regeneration — forced heating of the filter by the control system (can increase fuel consumption).
• 🔧 Mechanical cleaning — washing with special liquids (for example, Liqui Moly Pro-Line DPF Cleaner) or ultrasound.

Catalytic converter transforms harmful CO, NOx, CH to harmless CO₂, N₂, H₂O. It does not require regular maintenance, but may fail due to:

• 🛢️ Bad fuel (additives or high sulfur content).
• 🔥 Overheating (for example, if the ignition system is faulty).
• 💥 Mechanical damage (impacts to the exhaust system).

Filter type	Service life	Symptoms of a problem
Diesel Particulate Filter (DPF)	150–200 thousand km	Frequent regeneration, loss of power, error P2463 on the panel
Catalyst	100–150 thousand km	Deterioration in dynamics, metallic ringing when hitting the body, error P0420

6. Automatic transmission filter: why is it often forgotten

Automatic transmissions also have a filter - it cleans the transmission fluid (ATF) from metal shavings, friction dust and wear products. Unlike the engine oil filter, this element is replaced much less often, which often leads to premature wear of the automatic transmission.

There are three types of automatic transmission filters:

• 🧻 Paper - disposable, require replacement at every oil change.
• 🧲 Magnetic — catch metal particles, often installed additionally.
• 🔄 Reusable - metal mesh that can be washed (found in some models Toyota or Honda).

Where is the automatic transmission filter located?

• 🔧 In a box pallet - in most cases (requires removal of the pallet).
• 🔄 Inside the box - in some models (for example, ZF 6HP), which makes replacement difficult.

Signs of a clogged automatic transmission filter:

• ⚠️ Jerks or delays when changing gears.
• 🔥 Overheating of the box (can be checked using a diagnostic scanner).
• 🛢️ Darkening or burning smell in transmission fluid.

⚠️ Attention: If the filter in your automatic transmission has never been changed (for example, you bought a used car with mileage >100 thousand km), do not rush to do it yourself! In some cases, a clogged filter “holds” the remains of the clutches, and replacing it can lead to complete failure of the box. Contact a specialist for diagnosis!

7. Power steering filter: little known but important

Power steering (power steering) systems also have a filter - it cleans the hydraulic fluid from wear products of the pump, rack and hoses. Its availability depends on the design:

• 🚗 External filter - installed in a hose rupture (found in Mercedes, BMW).
• 🔧 Built-in filter - located in the power steering reservoir (for example, in Toyota Corolla or Volkswagen Passat).
• ❌ Missing - in some budget cars (for example, Lada Granta) there is no filter, which reduces the service life of the system.

Signs of a clogged power steering filter:

• 🔊 Whistle or hum of the pump when turning the steering wheel.
• ⚙️ Tight steering wheel rotation, especially at low speeds.
• 🛢️ Darkening or cloudiness of the liquid in the tank.

How often to change?

• 📅 With external filter: every 60–80 thousand km or when replacing power steering fluid.
• 📅 With built-in filter: only when replacing the tank (usually once every 100 thousand km).

8. When and how to change filters: universal rules

Each filter has its own resource, but there are general recommendations that will help avoid breakdowns:

1. Follow the manufacturer's instructions — replacement intervals are indicated in the service book. For Russian conditions it is better to reduce them by 20–30% (due to dust, bad fuel, temperature changes).
2. Consider your driving style:
   • 🏙️ City mode (frequent traffic jams) - filters clog faster.
   • 🛣️ The track means less dust, but higher load on the oil filter.
   • 🏜️ Off-road - air and cabin filters wear out 2-3 times faster.

Use quality spare parts — cheap filters can crumble, let dirt through, or cannot withstand pressure. Optimal brands: Mann, Bosch, Mahle, Framm.

Check filters when buying a used car — their condition will tell you how the car was used. For example, a clogged diesel particulate filter may indicate frequent short-distance driving (it does not have time to warm up).

Is it possible to clean the filter instead of replacing it?

• ✅ Yes: zero resistance filters, some cabin filters (washing), automatic transmission metal meshes.
• ❌ No: paper oil, fuel, air - they can only be replaced.

FAQ: Frequently asked questions about car filters

Is it possible to drive without an air filter if it is clogged?

For a short time (for example, to get to a service station) - yes, but no more than 100–200 km. Driving for a long time without a filter will lead to dust getting into the cylinders and accelerated wear of the piston group. In some cases (for example, after a water hammer), the engine may fail after just a few kilometers.

How to check if the fuel filter is clogged?

The most reliable way is to measure the pressure in the fuel rail with a pressure gauge. Normal values:

• ⛽ Gasoline: 2.5–4 bar (depending on the model).
• ⚙️ Diesel: 200–300 bar in Common Rail.

If the pressure is below normal, the filter is most likely clogged. Indirect signs: jerks during acceleration, long engine starts, loss of power.

What is the difference between a carbon cabin filter and a regular one?

The carbon filter has an additional layer of activated carbon that absorbs gases and odors (for example, from exhaust or chemicals). A conventional filter filters only solid particles (dust, soot). A carbon filter is more expensive, but indispensable for allergy sufferers or residents of big cities. However, its absorption capacity decreases over time - even if it is apparently clean, the coal becomes “saturated” and stops working.

Do I need to change the automatic transmission filter when changing the oil?

Yes, in 90% of cases. An exception is that if the filter is reusable (metal mesh), it can be washed. In most automatic transmissions, the filter is paper and is designed for one service life. If it is not replaced, old dirt will quickly contaminate the new oil, and the procedure will lose its meaning. In some boxes (eg. Aisin or Jatco) the filter is built into the pan and can only be replaced as an assembly.

Why does the oil pressure light come on after replacing the oil filter?

There may be several reasons:

1. The filter is leaking - check the O-ring (it may be left on the engine block from the old filter).
2. The filter is defective - the internal valve does not open, blocking the flow of oil.
3. The wrong type of oil is too thick for your engine (especially important in winter).
4. Oil pressure sensor is faulty - diagnostics required.

Actions: Stop the engine immediately and check the oil level. If the light blinks for more than 10 seconds after starting, do not operate the car until the cause is eliminated!