Is af­ter­mar­ket air fil­ter a prob­lem? Jury’s out

The Mercury News Weekend - - DRIVE - By Brad Bergholdt

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 brad­[email protected]; he can­not make per­sonal replies.

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