There is no great mystery to the operation of a car engine. It is essentially an air pump. The pistons and valves work together to draw in and expel air into the combustion chambers as the engine assembly spins round on the crankshaft.
The faster this assembly spins, the more air the engine can draw through. Add fuel to this air pump in the right amount to spark at the correct moment and the internal combustion equation is complete. Power! With so much air being drawn into the engine from the outside, it is of utmost importance this air enters the engine as clean as possible.
It is also important that this flow of air is not restricted in any way. The first line of defence an engine has to fight dirty air with is the air filter. Every molecule of air entering the engine comes through the air filter.
Not only does the air filter scrub the incoming air of harmful particulates, it should also allow the incoming air to flow freely.
Since every bit of dirt in the air flowing into the engine stays in the filtration material the air filter is made from, the air filter must be replaced at regular intervals.
A dirty and clogged air filter not only loses its ability to clean incoming air, but also offers a restriction to incoming flow. This restriction can result in poor engine performance and loss of efficiency. The good news is that changing an air filter is easy and inexpensive.
Where is it located?
The first step to changing the air filter is to find it. Open the hood and look for either a bread-sized box or merely the most plastic assembly atop the engine. Note locations and types of fasteners, clips, and hold-downs before removing anything. Or simply ask your mechanic. When you pull out the air filter it is typically flat and/or elongated, and is made of a paper element with rubber edges to seal it against the casing. Make sure not to poke anything into the airflow sensor. Air filters are cheap. Replacement airflow sensors are not.
Also take it easy on older, high mileage vehicles. Hard handling can damage intake hoses and tubes made brittle by years of exposure to engine heat. Back in the days of carburetted engines, the air filter was a big doughnut-looking unit that usually sat in a housing on top of the carburettor itself. Changing out the air filter involved removing the housing lid itself and swapping out old for new. Automotive engineers were able to become more flexible with engine intake configurations as fuel systems moved away from carburettors and into fuel injection.
When to change it
So how do you, as a car owner, know when it is time to change the air filter? That all depends, as is often the case with car parts, on how hard the car is driven and under what conditions. If the car sees much use in dusty, harsh conditions (think dirt dusty roads), then more frequent air filter changes are in order. If, on the other hand, you happen to be the typical Kampala driver who only does on home-work-home routine, you can get away with less frequent air filter replacements.
While permanent damage is remote, it is possible if you really neglect the air filter for a long time. If an air filter were sufficiently dirty and damaged, it could allow contaminants into the combustion chamber. In any case, it is a smart and proactive policy to at least inspect the air filter every 10,000km. It costs nothing to look, and it could save you from expensive repairs down the road.