With my philosphy of "If it Ain't Broke, Don't Fix It" I was wondering if I was replacing my air filter when it wasn't needed. So I thought of a test that might give me the answer.

So I made 3 runs each of about a mile up hill with the old filter, no filter and a new filter. I started at 50 MPH and ended up at about 57 MPH and also timed the runs with a stop watch.

Without listing all the data there was virtually no difference in either the top speed or the elapsed time of any of the conditions that would would show any difference.

Checking the mileage for the last 1200 miles, I got 30 MPG.

Conclusion: Air filter did not have to be replced. So I gave it a good blow job with an air hose nozzle and reinstalled the used air filter. I'll check it again in about 25,000 miles. The test car is rarely driven on dirt or dusty roads so your results may differ if you drive in dirty or dusty conditions.

P E H

The airfilter in our Jetta is on a 20,000 replacement by VW spec's and they could probably easy do 30,000 miles in our driving. I don't know about the 240D, but it could probably go 20,000 in our driving conditions fairly easy.

__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

Maybe I should just weld the hood shut. My friend gained a few mpg when he changed his old airfilter, on his E300D. Remember these are turbo charged engines so the filter would have to be very bad to affect performance. But if the turbo has to work harder mileage will go down. I will change mine every 2 years with one cleaning in between.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Oldnavy,

How can anyone write a spec for air filter replacement if that person doesn't know the conditions in which the filter is used.

So they probably specify replacement for worse case conditions. They also make more money if you replace your filter more than necessary by selling you more filters.

However, even their worse case conditions would not apply to an OK duststorm where a fiter could be plugged in a few miles.

P E H

I change mine every oil change (or every other, depending on my mood), and these days that either four or two times a year. I live in an agricultural area, and right now everyone is taking advantage of the nice dry weather to combine soybeans and corn -- dust EVERYWHERE. I washed the cars last weekend and they are yellow now.

Air filters are cheap, change often. On the turbos, you will notice more than normal turbo lag and higher idling tubo "whine" (if you can hear it -- the Volvo sounds like a police siren a block or so behind you!). More dirt will make it thorugh a dirty filter than a clean one, reguardless of blockage, they are "depth" filters.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I'm going with PEH on this one. Too many filters , spark plugs, distributer caps, and many other things are replaced needlessly, because there is a dollar to be made. When I ran my shop I never replaced these items unless they were due for replacing. I'd rather spend my client's money on preventive maintenance where it was really needed. The commercials tell you to get your car tuned up to improve fuel mileage and performance. Years ago I had a 79 Toyota that hauled ass and sipped the fuel. One day it started to die on me and was hard to start. I decided to check the plugs which was something I had not done in years. The gap was about 95 thousanths. It was time to replace the plugs. Now I'm not suggesting you run your car til it dies, but I'm saying that a good mechanic knows when it is time. Remember wax on wax off.

Peter

__________________
Auto Zentral Ltd.

I thought that's what I said. The spec is just a figure the engineers came up with some way. I just visually check mine an on ocassion and replace if I deem it needs replacing. Car has 42,000 miles and is on 3rd filter and 4th oil change. If I changed by oil sample report I would still be on third oil change for another 8,000 miles. But if I go too long at my age I might forget how to change the oil & filters.

__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

Here's an idea for the experimenters in this forum.

Install a vacuum gauge between the air filter and the turbo inlet.

I expect the vacuum level to be too low low, in the "inches of water" category, for a regular gauge to be effective, but have no other guess.

Atmospheric pressure = 1 Bar = 30 inches of mercury = 14.7 psi = 33.9 feet of water

So, 1 psi = 27.7 inches of water. A water column makes a very sensitive gauge.

I expect pressure fluctuations, so a mechanical gauge might not be the best, unless properly damped.

(I just pictured someone driving around with a water bong on their hood.. )

Record the vacuum with a new filter. I would expect to find a range of vacuum readings, depending on RPM and load and boost.

Put the 'dirty' filter back in and record again. I expect the dirtier filter to result in higher vacuum readings under all conditions.

P.E. Haiges, you would then be able to decide, based on a vacuum reading, that the filter is dirty. Also, you could see if cleaning is as good, for practical purposes, as a new replacement.

Ultimately, replace the gauge with a vacuum switch and warning light.

Best regards,
Jim

Air filter intervals really depend on conditions where you drive. In some areas, with a good amount of rain, air filters are probably changed more often than necessary.
If you do much driving in areas like west Texas it becomes more critical. They use an extremely hard caliche clay to surface dirt roads there. When it breaks down it is like talcum powder and gets into everything. Most of this damaging "grit" cannot be seen very well.
I have heard from several Powerstroke mechanics of "sanded" turbos due to owners not changing air filters because they did not appear dirty.
If you have been driving in dusty conditions, it really makes more sense to me, to change the air filters even more often. Air filters are much cheaper.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

OK, P E H, you hit another hot button, nothing personal....
I have no issue with how or if ever you change filters, it is your car.
I do have an issue with people who try to create their own pseudoscience.

This is not a test; it is a placebo with an opinion.
Air filter testing generally costs $3 - 7 million dollars and consumes 18 - 20 vehicles on three continents.
Do you have a calibrated flow stand?
Do you have calibrated particle detectors?
Can you give me the particle density incoming to the filter housing?
What is the particle density entering the intake manifold?
Do you have a mechanically - electrically perfect, thoroughly instrumented, calibrated, blueprinted and wind tunnel tested vehicle?
I have built them and run a durability fleet; there are many professional durability drivers in the Detroit metro area because of the OEM durability fleets running 24 X 7 X 365.
The specification for replacing air filters is a compromise, based on the theoretical average driver and geographic location.
The OEM's count on people not following the listed maintenance to void warranties.
I will not go into the 1200 to 3000 data points needed to certify just air filters and set durability change intervals.
I could arrange for your car to be instrumented properly for the type of data you seem to want, cost would be $185,000.00 - $268,000.00 and would cover only one hundred twenty eight channels with no video, UV or thermal imaging.
For minimum data to be valid, you would need 900,000 miles or nine duplicate vehicles run to 100,000 miles.
Data acquisition and record keeping must be Legal court ready at every moment, with no breaks in the evidence chain.



FYI:
For those who may not know the term pseudoscience.

http://skepdic.com/pseudosc.html
pseudoscience
A pseudoscience is set of ideas based on theories put forth as scientific when they are not scientific.

Scientific theories are characterized by such things as (a) being based upon empirical observation rather than the authority of some sacred text; (b) explaining a range of empirical phenomena; (c) being empirically tested in some meaningful way, usually involving testing specific predictions deduced from the theory; (d) being confirmed rather than falsified by empirical tests or with the discovery of new facts; (e) being impersonal and therefore testable by anyone regardless of personal religious or metaphysical beliefs; (f) being dynamic and fecund, leading investigators to new knowledge and understanding of the interrelatedness of the natural world rather than being static and stagnant leading to no research or development of a better understanding of anything in the natural world; and (g) being approached with skepticism rather than gullibility, especially regarding paranormal forces or supernatural powers, and being fallible and put forth tentatively rather than being put forth dogmatically as infallible.

Some pseudoscientific theories are based upon an authoritative text rather than observation or empirical investigation. Creationists, for example, make observations only to confirm infallible dogmas, not to discover the truth about the natural world. Such theories are static and lead to no new scientific discoveries or enhancement of our understanding of the natural world.

Some pseudoscientific theories explain what non-believers cannot even observe, e.g. orgone energy.

Some can't be tested because they are consistent with every imaginable state of affairs in the empirical world, e.g., L. Ron Hubbard's engram theory.

Some pseudoscientific theories can't be tested because they are so vague and malleable that anything relevant can be shoehorned to fit the theory, e.g., the enneagram, iridology, the theory of multiple personality disorder, the Myers-Briggs Type Indicator®, the theories behind many New Age psychotherapies, and reflexology.

Some theories have been empirically tested and rather than being confirmed they seem either to have been falsified or to require numerous ad hoc hypotheses to sustain them, e.g., astrology, biorhythms, facilitated communication, plant perception, and ESP. Yet, despite seemingly insurmountable evidence contrary to the theories, adherents won't give them up.

Some pseudoscientific theories rely on ancient myths and legends rather than on physical evidence, even when their interpretations of those legends either requires a belief contrary to the known laws of nature or to established facts, e.g., Velikovsky's, von Däniken's, and Sitchen's theories.

Some pseudoscientific theories are supported mainly by selective use of anecdotes, intuition, and examples of confirming instances, e.g., anthropometry, aromatherapy, craniometry, graphology, metoposcopy, personology, and physiognomy.

Some pseudoscientific theories confuse metaphysical claims with empirical claims, e.g., the theories of acupuncture, alchemy, cellular memory, Lysenkoism, naturopathy, reiki, rolfing, therapeutic touch, and Ayurvedic medicine.

Some pseudoscientific theories not only confuse metaphysical claims with empirical claims, but they also maintain views that contradict known scientific laws and use ad hoc hypotheses to explain their belief, e.g., homeopathy.

Pseudoscientists claim to base their theories on empirical evidence, and they may even use some scientific methods, though often their understanding of a controlled experiment is inadequate. Many pseudoscientists relish being able to point out the consistency of their theories with known facts or with predicted consequences, but they do not recognize that such consistency is not proof of anything. It is a necessary condition but not a sufficient condition that a good scientific theory be consistent with the facts. A theory which is contradicted by the facts is obviously not a very good scientific theory, but a theory which is consistent with the facts is not necessarily a good theory. For example, "the truth of the hypothesis that plague is due to evil spirits is not established by the correctness of the deduction that you can avoid the disease by keeping out of the reach of the evil spirits" (Beveridge 1957, 118).

See related entries on ad hoc hypothesis, cold reading, communal reinforcement, confirmation bias, control study, Occam's razor, pathological science, the placebo effect, the post hoc fallacy, pseudohistory, science, selective thinking, self-deception, subjective validation, and testimonials.

further reading

Dawes, Robyn M. House of Cards - Psychology and Psychotherapy Built on Myth, (New York: The Free Press, 1994).

Gardner, Martin. Fads and Fallacies in the Name of Science (New York: Dover Publications, Inc., 1957).

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Prototype R&D/testing:
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Um... politely speaking, the vacuum gauge is a tried and true indicator for the equipment operator, and a good investment if your diesel is high value (trucks have them on the dash). Then call the filter manufacturer and talk to the folks that designed the thing, not the salesman. They've already spent the coin to do the testing and know at what differential pressure the filter should be changed. This all assumes the filter doesn't leak or get crapped up with oil (not an issue with daBenz's oil bath filter).

__________________
daBenz - 1970 220D

last time i replaced mine my daughter said "gee dad, that's like REALLY GROSS"

and it was....

not exactly a scientific test but nonetheless the truth!

__________________
1984 300D Turbo - 231k....totalled 11/30/07 RIP

Vacuum gages for air filters are supplied on Freightliner MT-35, MT-45, MT-55 chassis, they are also now on Dodge Cummins diesel trucks and are used by many turck company's for monitoring the air filters.

__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

Anyone seen those things on some newer autos, heavy trucks, etc? Perhaps the vac gauges everyone is talking about, I have never taken a close look at them. They have some colored plastic in them and say when your filter should be changed, vehicle specific I assume. They seem to be pretty inexpensive looking (hah) and could probably easily be added to a stock air cleaner setup if someone was truely afriad of clean, easy flowing air problems.
When mine (air cleaner) changes color...I replace it. SImple enough.
(shug)

Thanks for the enlightenment on vacuum gages, maybe not such a wild idea after all.

Now, aren't diesels an "excess air" combustion, where there is always more air than needed to combust the fuel injected? If so, how dirty would the filter have to be to drop airflow until performance loss was noticeable?

I guess I'll just change mine at suggested intervals.

Best to all,
Jim