Air filter interval

One more vote for air intake location.

I forgot to mention that the same car which dirties filters fast also
dirties oil fast. Although it is low mileage, oil turns dark in a few
thousand miles. My other, high mileage car, keeps both oil and filters
clean for a long time.

I don’t know. I change filters between ten and twenty thousand and oil at three and five thousand depending on the car. Some have said the new oils darken quickly but that has not been my experience. Might be you have environmental issues, driving pattern with short trips, or something.often my cabin filter is filled with bugs and fuzz though.

Other than for warranty maintenance mileage intervals, I refuse to push air filter replacement unless it is starting to turn black or looks like a rats nest… I have ran 75K on a van with the OE air filter, 124K on one car, 78K on another car and when I changed them was cause I was doing a major mileage “tune up” or one was for a recall and they said I had to replace the filter, but didn’t changed the MPG at all on any vehicle…

Years and years ago I read an article about old school air filters like you would find on any hotrod just about…
They took a $1.99 Purolator, K&N, IIRC Accel & Holley (but 3 performance and 1 cheapy air filters 14 in. Diameter, 2 in. Tall, Each), and put them on the flow bench, non of them even registered (too many CFM’s), so they duct taped half the filters off (so 1/2 clogged/stopped up) and they still Flowed over 3,000 CFM’s each including the cheapo one… At 3K CFM’s that is still over 3X what the 1970 LS6 450 HP engine used… So meaning that a 14" X 2" round air filter 3/4 clogged was still more then the 450 HP engine could use…

Obviously some vehicles air filters depending on inlet to filter routing and or climate you are in will differ, but I very rarely change engine air filters or sold them…

With all the sensors on the intake side, how hard would it be to measure pressure drop and light a ‘replace air filter’ signal on the dash when needed?

I actually keep one or two air filters on the shelf for when I need them. Then just order replacements. Oem are not readily available and saves time if you are checking the filter anyway. Might as well just put a new one in.

I will say though that years ago I used a fram filter on my olds instead of an ac. I had a noticeable increase in noise so just stick with oem.

How leaky are the air handling systems? I ask because rather than ever increasing pressure drop across the filter the air might leak out at some higher pressure. leveling pressure drop might be an indication to replace the filter, but the leaks might occur well before air flow through the filter becomes problematic.

It would be easy.

Just need a differential pressure switch.