In general. the average life of a car is around 3,00,000 km. For a moderate driver who travels 100 kms a day it will take 8 years to travel this distance. During this time, there will be a need to replace some of the parts for a better functioning, as not all parts are made to last for the entire life time of a car. These parts are present in various systems like fuel delivery system, transmission system, starting and charging system, braking system, cooling system, lighting system, steering and suspension system, etc. Among the above mentioned systems, parts in fuel delivery system, starting and charging system and braking system are commonly replaced. Based on the age of vehicle, some of the system parts are replaced more than thrice in its life time.
Air filter
Air filter is present in the fuel delivery system of the car, which filters the air entering the into the combustion chambers of the engine. If the air filter is not replaced, it can reduce the efficiency of the car and create friction between piston and cylinder. Air filter is replaced when cleaning of air filter does not yield any improvement.
Fuel filter
It is another part in the fuel delivery system, which removes contaminant particles from the fuel. It is present between the fuel tank and fuel pump in a car. In case of a petrol powered engine, sediment bowl along with fuel filter is used. Fuel filter is replaced every 3 years for better functioning of a car.
Oil filter
Engine oil used in cars lubricate parts of the engine and with time engine oil gets more viscous by gaining small metal particles or any other dust particles. Oil filter is used to separate these contaminants from the oil. Oil filter must be cleaned or replaced for every 5000 km.
Fuel pump
Fuel pump is the most important part in fuel delivery system of a car. It supplies the required amount of fuel to the engine. In cars, fuel pump is operated continuously and it suffers from wear and tear. Many manufacturers suggest changing fuel pump for every 5 to 6 years.
Brake pads and components
Brake pads are present in braking system of a car and they are the main source of stopping a car. 
When brake pedal is pressed, pads hold the rotating disc with a high pressure, and sometimes this may result in wear of material.
It is recommended to change brake pads every 80,000 Km. Other components in braking system like wheel cylinder, calipers, master cylinder are changed for every 1,50,000 Km.
Tyres
Many car tires are subjected to wear with time. As the tyres indirectly impact the mileage, many manufacturers recommend replacement every 1,00,000 km. A car with insufficient air pressure capacity inside the tyre will result in higher inertia while moving.
Clutch
Clutch is present in the transmission system of a car. They transmit the required amount of motion to the gears from the crank shaft. As they operate under the action of friction between the plates, it also results in wear after some time. So, it is recommended that clutch needs to be changed for every 1,50,000 Km.
Alternator
This is an electrical part present in the starting and charging system, which supplies required amount of electrical energy to the various parts in a car. In case of any problem with alternator one must test wiring and connections, and then go for a alternator change.
Just like humans, cars also require more attention with age, especially to the most critical parts that are needed for ongoing survival. As the vehicle accumulates mileage and wear, replacing these critical parts at required time ensures better functionality and steady performance.