Is aftermarket air filter a problem? Jury’s out

Is it true that an aftermarket high-performance air filter can cause problems with how a car runs? I recently had a surging condition, and my mechanic fixed it but insisted I go back to the original air filter. What do you think? — Adam B.

This is a controversial subject! There is considerable discussion and misinformation circulating regarding possible mass airflow (MAF) and intake air temperature (IAT) sensor contamination due to cotton gauze air filter oil causing problems. A contaminated MAF sensor can cause both irregular engine and transmission performance. It’s also understandable that car makers aren’t fond of after market modifications, and some service facilities aren’t thrilled with lifetime air filters as they reduce revenue. On the other hand they could include a fee to clean and re-oil them!

A properly maintained washable cotton/oiled air filter is claimed to increase airflow, trap more dirt before requiring service and reduce waste.

For what it’s worth I researched this topic fairly deeply, speaking with technicians, searching for technical service bulletins and digesting K&N’s (leading washable air filter company) test results. The techs seem about evenly split; the general consensus being that a consumermaintained product is a wild card for proper functionality! Over-oiling a filter is believed to be a problem, backed up by service bulletins such as GM’s #04-07-30-013D stating that it can cause the performance problems above, as well as a possible illuminated MIL (malfunction indicator or “check engine” light).

K&N disputes implications that their filters can cause problems, backed up with what I believe are compelling test results. They studied “damaged” MAFs returned for inspection and found only a portion were contaminated, and the contamination was either silicon (leaked potting material from within the sensor) or dirt and not oil. The environment the MAF lives in is subject to PCV (positive crankcase ventilation) fumes which contain sticky carbon particles. It’s one reason why someMAF systems employ a burnoff function to maintain cleanliness. K&N also over-oiled a filter by 30 percent and subjected it to very high airflow rates for some time and couldn’t detect any loss of oil from the filter. I wonder if there may be some consumers who don’t clean their filter properly, then add perhaps much more oil than this? A final study done by K&N was to submerge aMAF sensor element in their oil and performance test it afterwards. The sensor readings were skewed at first, but after airflow removed the oil, the readings became identical to the original clean values.

I’mon board with a washable air filter, as long as it’s properly maintained. Thismeans never using a brush or compressed air to remove deposits and following the appropriate procedures for cleaning and re-oiling on schedule. I’mthinking aboutmine as I write this— I know it’s not overoiled but withmy dusty environment it’s got to be ready for cleaning!

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.