Oh, the humble air filter. Destined to toil away in darkness, it's often ignored when performing regular maintenance. That's a shame, because a clogged air filter can have dire consequences. In the short term, the additional restriction can dramatically decrease fuel economy and increase emissions-- a dirty element can increase fuel consumption by 10% or more. Should the filter pass dirt through to the delicate inner workings of the engine, severe damage can occur. Fortunately, it's usually quite straightforward to service the filter element.
[Click through to walk through the task of air-filter R&R...]
In this case, we'll be taking a look at what's involved in cleaning the K&N reusable air filter in a 1996 GMC K2500. As sharp-eyed readers have already figured out, this vehicle sees quite a bit of use in dusty conditions, and as such should receive filter maintenance on a frequent and regular basis. Of course, I'm a bit ashamed to admit that the airbox lid hasn't been removed since the K&N filter element went in about 40,000 miles ago, and according to the Donaldson filter condition indicator, it's about time that something is done. You'll want to check your owner's manual for the proper air filter service interval, but typically it should be performed every 15,000 miles or so.
In the case of this vehicle, removing the airbox lid is as easy as unsnapped two latches. Trucks are typically designed for easy service in the field due to the large number of professional users; most passenger cars will require some simple tools (often just a screwdriver) to remove the lid. It's a good idea to wipe the lid clean before removing it to reduce the amount of dirt that allowed into the airbox.
Upon removing the lid, we see the filter element. Yep, it's dirty.
In this particular case, the filter element is clamped to the induction system, so a screwdriver is used to loosen the clamp and remove the element. Many vehicles have a "drop-in" cartridge that will require no tools to remove.
For those that live in colder climates, it's highly likely that mice have attempted to make a home somewhere in your vehicle (its warmth makes for an attractive building site). Here, we see that the critters have tried to set up shop in the airbox. A shop vacuum is carefully used to remove this sort of debris.
For those using a non-serviceable disposable element, you'll be skipping past this part and will be moving on to the step of installing a fresh filter.
We start off our K&N cleaning process by promptly ignoring the manufacturer's warning not to use compressed air. We're careful not to cause filter damage and turn down the regulator on our compressor to about 40 PSI. The goal here is simply to remove any loose dirt or debris (such as, say, a mouse nest).
Next, we use a soft-bristled brush to remove any addition loose dirt. Discarded toothbrushes work great for this task; just make sure it doesn't end up back in the bathroom when you're done.
Cleaning and re-oiling the element is the next step. While we've used ordinary dish detergent and automatic transmission fluid for this part of the job in the past, we decided to try K&N's Recharger kit this time around. It was approximately $10 at the local parts store, and we're guessing that there is enough cleaner and oil to clean the filter perhaps 15-20 times.
We spray down the filter with the cleaner, and wait five minutes or so. Repeat this routine a few times, and then take the filter to a sink and rise it with hot water. We elected not to take pictures of us performing this task in the kitchen sink, as we're smart enough not to present our significant others with photographic evidence of such offenses. Running the filter through the dishwasher would probably be ideal, but we've been banned from using that appliance due to a previous parts-cleaning experiment.
When the filter is properly cleaned, the cotton gauze element should have no remaining signs of dirt or the reddish-colored oil. Now we wait for it to dry. Once again, K&N warns against using compressed air, and once again, we tend to ignore such warnings. We would suggest heading the manufacturer's recommendation not to use a heat gun to accelerate the drying process, as we've found the metal screen of the filter does a great job of transferring that heat directly to our skin. If you choose to let the filter air-dry, expect it to sit overnight.
We then apply the oil according to the manufacturer's recommendations. Use several light coats, and let the oil wick into the element between applications.
The goal is to have an evenly oiled element using the bare minimum amount of oil. Excessive oil can get drawn into the engine and cause a variety of problems, especially on vehicles with mass airflow sensors (the oil tends to foul them and can cause a Service Engine Soon light and a variety of drivability problems).
Reinstall the filter, close up the airbox lid, reset the filter condition indicator (if your vehicle is equipped with one), and mark the task as completed in your maintenance logbook. Plan on performing this job every few oil changes, and you'll be well ahead of most car owners.