When you take your Toyota Surf for a routine service, such as a tune-up or oil change, the mechanic will probably also take a look at the air filter. The air filter, although a small and seemingly unimportant part, is crucial for ensuring your engine has all the clean and cool air it needs to operate optimally. There are many reasons why the air filter might need to be replaced, but one thing is for sure - it does need to be replaced regularly, on average every 50.000kms or so. This is just a rough estimate, and the type of driving you typically do is what really matters. But before I talk about how often you should do it and what the signs of a faulty Toyota Surf air filter are, let's see what air filters do, and what type of aftermarket air filters you can find when looking for a replacement.