Every time you need to change oils, look for the bright light through the air filter. Automotive air filters like the Purolator Automotive air cleaners typically have visible lights you can see upon opening the engine. If you can't see any light, that means your filter is dirty and you need to take it out. You can have someone do it for you or you can do it yourself. After you remove it, apply the cleanser on the dirty side of the filter and leave it for about ten minutes. This is for the cleanser to loosen all the dirt and for you to be able to rinse it easier. After ten minutes, make sure you rinse it out thoroughly and leave it to dry for 20 minutes. Absolutely don't oil it if it's not yet completely dry.