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Air Filter

Will changing to a K % N air filter improve my gas mileage at all? See them in ROAD AND TRACK magazine with great claims, and high prices…


I’ve tried K&N filters on 3 vehicles (95 Dakota, 93 Caprice, and 2000 Blazer) and haven’t noticed any increase in mpg.

Ed B.

What many used oil analyses show, though, is an increase in silicon (dirt/dust) getting into the oil, thru the filter. Not good. I am convinced OEM style air filters is best. If anything, change more frequently.

There are a few vehicles with silencers designed in to the air boxes that are somewhat restrictive and do limit air flow at high RPM. On the rare occasion that people see a performance gain from aftermarket air filters, it is because they took off the silencer when they put on the new filter. They get a little more power, little to no effect on gas mileage, and a lot more engine noise (whoop sound).

Absolutely avoid oiled filters unless you will really keep them oiled as recommended. Most people don’t. I once was looking at buying a clean low mileage 3-series BMW, but I ended the inspection and walked away the moment I saw that the air box was gone and an oiled air filter had put on its place.

In the words of Click and Clack, claims made by aftermarket air filter vendors are booooogus.

All the above, and here’s why: your mpg has nothing to do with how easily air gets through the filter, unless you drive with your foot on the floor at all times! At all other times, reducing (slightly) the air resisitance of the filter is compenstated by increasing (slightly) the air resistance at the throttle plate. So those filters are a waste of money unless you’re after absolute maximum wide-open-throttle horsepower.

The best thing about the oiled filters is a slight improvement in power. For MPG, it really isn’t the way to go. You’d make much better gains by just easing out of and into the throttle with your foot. In order to get the best performance, you usually have to replace the silencer as already mentioned. But then, the gain is power, not MPG typically.

Do a google search for “miata air filter test” and you’ll find a pretty careful study that concluded: 1. Most aftermarket high performance air filters let more dirt into the engine and 2. On the Miata at least, the stock air intake plumbing is more restrictive than the stock filter.

I would post the link to the study, but I don’t want to get censored again.

I like your point #2 - the filter may not be the ‘weak link in the chain’. When I was modifying my GTI I remember a similar article regarding flow testing modified intake manifolds. They kept trying to improve things, and found they could saw off the majority of the manifold with no effect - it was the intake runners and valve areas that were controlling flow!

Very little gain in power, maybe even a little loss, no gain in mileage. While there is some evidence of possible engine damage, I also believe that is also very small and unlikely, except for cars with MAFs Just a little too much oil on the filter and by by MAF.

Check out:

In short, don't bother

Strange that you identified the magazine but not the vehicle. This is called Car Talk not… If it’s an 05 Ford E-150 Van with a 4.6 engine and power options with automatic transmission, the original filter looks almost like a K&N. I think it wouldn’t help on that van. The 02 GMC Sierra with a 4.8 has a huge filter and doesn’t need help either. If you make a paper airplane from the page with the filter on it and it flies farther than a page without the filter, I would want to try the filter.

Another major caution for K&N style oiled air filters ( truck in our shop today for this reason ). Watch the placement of your air flow sensor in relation to the air filter, If the filter is first in line and the air flow sensor is after, The oily residue is sucked toward the engine getting onto , and affecting the performance of, the air flow sensor.
Only use a K&N style filter AFTER an air flow sensor.

Only use a K&N style filter AFTER an air flow sensor.

Would that then allow all the dust etc to damage the air flow sensor?

Perhaps, but have seen many with bugs in them. 10/22/08 in our ford dealer shop I gave out a ziplok bag to a tech to …save the bug for the customer to see !!:slight_smile:

The issue I would like to comment on is that the OP says he has "seen them in R+T

Now I would like to think every product that appears in the back section of a major automotive mag has been tested by the Editors, but that is not the case.

There are some very questionable non-automotive products advertised in the back of these mags.

The vast majority of the time MAF’s burn up because when cleaning an oil-gauze air filter many people over oil them. The excess oil builds up on the sensor and it burns out.

I agree with Jay-, they have less restance but allow more dirt to get into the engine