Q: During my car's last routine service, the workshop replaced the air filter. It was the first time the air filter had been replaced. What does this filter do and is it necessary to replace it? Also, what other filters does a car have?

A: The air filter is part of the engine's intake. It cleans the air that is drawn into the engine so as to prevent any contaminants, such as fine sand or debris, which can damage the cylinder walls.

Over time, the filter gets choked, airflow becomes restricted and engine performance dips.

Air filters usually cost between $15 and $100. They should be replaced at least after every 25,000km. Some are washable, but you will have to be somewhat of a handyman to gain access to the filter, remove and reinstall it after cleaning.

Most original air filters are not washable. These are much cheaper than after-market washable types.

Also often overlooked is the air- conditioning system's filter. Located inside the cabin and in the fan section of the air-con blower, it filters out particles or pollutants in either the incoming fresh air or recirculated air.

It is important to have the filter periodically cleaned or replaced to maintain a clean and healthy cabin environment.

The most commonly replaced filter on an internal-combustion engine is the oil filter.

It is replaced whenever you do an oil change.

All petrol and diesel engines also have fuel filters, which prevent contaminants from flowing into the carburettor, injection pump or injectors. Inline fuel filters easily last up to 120,000km, while in-tank filters found on most fuel-injection cars last twice as long.

More often than not, the fuel pump requires replacement before that and as these filters are part of the fuel module, they would be included in the new unit.