The foam pad that is attached to the air filter is called a pre-filter and it’s there as an added layer of protection for the filters of vehicles that are driven in severe conditions.
To some this might be a glaring observation, but others? Not so much. Spend a little time on the youtube.com DIYer channels and you’ll see what I mean. The purpose of a pre-filter is to stop larger pieces of debris from getting stuck in the filter’s pleats and prematurely restricting airflow. It’s a well-intentioned addition for certain makes and models, but has led to quite a bit of confusion, particularly in the DIY community.
Part of the reason for so much confusion is because of discrepancies in the way OE and aftermarket suppliers’ catalog certain applications. Sometimes you might find that the OE manufacturer has a part number cataloged for a certain application, but an aftermarket competitor has 2 different part numbers cataloged for the same application.
Let’s take the vehicle from the Youtube video link above for example– for the 2011 to 2018 Volkswagen Beetle 2.0L, there is only one recommended original equipment filter, VW part number 5C0129620; an air filter that does not feature a pre-filter. Yet, if we search the same application using another popular European supplier such as Mann, we’ll find two part numbers available: C 35 154 (without pre-filter) and C 35 154/1 (with pre-filter).
In that situation there is the potential for someone to remove an air filter that does not have a pre-filter, then remove the new filter from the box to find that it has a pre-filter, and immediately begin questioning whether they’ve purchased the right filter.
Should the Pre-Filter on a Car Air Filter Be Removed?
If a new air filter has a pre-filter attached to the pleats, there is no reason to remove it. Yes, as we mentioned above, it is possible that the dirty filter that was removed did not have a pre-filter, but that doesn’t mean the new filter with pre-filter is wrong. It simply means that there are filter suppliers out there that are offering both options to cater to vehicles that may be driven in a variety of conditions and regions with harsh road conditions or seasonally fluctuating climates. Someone who drives the above-mentioned Volkswagen beetle in normal conditions, which is to say mild weather, well-kept roads, clean environment, etc., will do just fine without a pre-filter. Someone who drives that same vehicle in more severe conditions where it’s always hot and dry or extremely cold, or both with fluctuating seasonal climates, will benefit from the pre-filter option because larger debris such as leaves, and pine needles won’t clog the filter pleats so quickly.
What if My Air Filter Has a Pre-Filter but I Don’t Drive in Severe Conditions?
If you’ve purchased an air filter for your car and it has a pre-filter, but you don’t drive in severe conditions, you’ve got nothing to worry about. But first, are you sure you don’t drive in severe conditions? In reality “normal” driving conditions are very rare. Most people drive in what is considered “severe” conditions and don’t realize it. So, if you buy an air filter that has a pre-filter attached, but the one you’ve removed from your car does not – there is nothing to worry about. The pre-filter will not impact airflow in anyway and certainly won’t impact the performance of the car in any noticeable way. Leave it in place.