Better check now: How dirty is your car’s air filter?

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Tim
Update by Tim Suddard to the Porsche 911 Carrera project car
Jan 20, 2023 | Porsche, 997, 911, Porsche 911, Porsche 997, K&N, Air Filter

Our Porsche 997 had covered less than 25,000 miles and came to us looking clean. But was it all that clean?

Not the air filter.

We ordered a replacement filter directly from K&N’s website. It cost us about $85 shipped to our door. (We figure this car is a keeper.)

Installation is straight forward. You just carefully remove the airbox but watch out for hoses that attach at the bottom. A Torx bit is used to disassemble the box. Then just pop the filter in and reassemble everything.

Now the car is ready to head back to the FIRM so we can test our new tires and brakes.

[The Grassroots Motorsports ultimate guide to track car lap times]

Have you checked your air filter lately? It’s time, isn’t it?

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Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
1/19/23 5:03 p.m.

queue arguments on whether cloth/oil filters are better or worse than paper!!

Peabody
Peabody MegaDork
1/19/23 5:40 p.m.

On PW's last car, which usually got timely service, I somehow forgot to replace the air filter and only realized it at 7 years and 160k.

It was dirty.

Changing it made no perceptible improvement in fuel economy or performance.

gearheadE30
gearheadE30 Dork
1/19/23 5:43 p.m.
Peabody said:

On PW's last car, which usually got timely service, I somehow forgot to replace the air filter and only realized it at 7 years and 160k.

It was dirty.

It made no perceptible improvement in fuel economy or performance.

This is how my GMT400 air filters are. Ran one about that long on the K1500 not realizing it, it was visibly dirty but never tripped the restriction indicator and no change in performance.

The 8.1 on the other hand moves a lot more air and has about half the air filter surface area. I've got something like 15K miles on that filter and it already looks bad enough to replace. Unfortunately, not a lot of good options for airboxes with more filter capacity on this one.

WillG80
WillG80 GRM+ Memberand Reader
1/19/23 5:55 p.m.

I like the visual indicators some trucks have on the intake. I have a suspicion most people change their air filters way too often, or not nearly enough. I previously did 10k mile intervals but go much longer these days. 

outasite
outasite HalfDork
1/19/23 7:25 p.m.

Back in the 70s working in a Mopar dealership. Customer pulled in from the interstate concerned about the performance of a slant 6 automatic Valiant. Pulling it into the shop I noticed rough idle and poor brake performance. Opened hood, removed air cleaner housing cover and idle smoothed out. Removed a very clogged air filter, installed new air filter and happy customer was on their way.

Toyman!
Toyman! GRM+ Memberand MegaDork
1/19/23 8:06 p.m.

The one in the Touareg must have been original. I assumed since it had been inspected and service the dealer had at least checked it. 

Wrong. It collapsed a month after I bought the car and ended up in the turbocharger. 

I checked the Bentley the day I bought it. It may have been original as well as it was almost black. 

spitfirebill
spitfirebill MegaDork
1/19/23 8:26 p.m.

I've never changed an air filter where I could tell a difference.  

rslifkin
rslifkin UberDork
1/20/23 8:51 a.m.

On EFI cars, a dirty filter won't make it run badly, hurt mpg, or anything else, as the ECU knows how much air it's getting.  It's not like a carb where a dirty filter can skew the throttle position vs airflow relationship and cause issues. 

The worst thing that'll happen with a dirty filter on anything even remotely modern is that it'll lose some power when the filter can no longer flow enough. 

outasite
outasite HalfDork
1/20/23 10:08 a.m.

Another reason for regular inspection: Air filter housings are great for critters to set up house/store food/use air filter material for bedding.

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
1/20/23 1:10 p.m.
Robbie (Forum Supporter) said:

queue arguments on whether cloth/oil filters are better or worse than paper!!

3rd option: AEM Dryflow FTW!

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