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What dP for my air filter change #5164900 07/19/19 05:41 AM
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dnewton3 Offline OP
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I installed a Wix 24801 air filter dP gauge on my new 3.5L Duratec Taurus. My (reasonably) new filter exhibits a vacuum of 11" after a couple of WOT runs.
https://www.amazon.com/WIX-Filters-24801-Filter-Service/dp/B0014BI1KA
The product is actually made by Donaldson; the little paper of install instructions references Donaldson by name.
The gauge goes up to 25" and then would indicate a change is due. I'm not sure if the 25" value is sane or not; these are generic and not specific to any application.

I am also considering installing one on my 6.2L F250 gas truck as well.

I'm open to suggestions; at what vacuum would I consider an air filter change, and why? State your value and reason behind the suggestion, please. Would it be the same for each engine, or different?



Last edited by dnewton3; 07/19/19 05:43 AM.

The act of preventative maintenance, in and of itself, is FAR MORE important than brand/grade/base choices among lubes and filters.
- under maintaining something is akin to abuse/neglect; that can kill equipment by shortening the lifespan
- over maintaining something has never been proven to be anything but a waste of time and money
Re: What dP for my air filter change [Re: dnewton3] #5164990 07/19/19 07:28 AM
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MParr Offline
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dnewton3
I don’t know a whole lot about those things. Our maintenance shop had them installed on all our diesel powered trucks. They didn’t change the air filter until it reached the RED range or required maintenance intervals. They would just reset it after the filter change and monitor it at every oil change. On average, the air filters were changed at 15,000 miles whether the meter hit the RED range or not.


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Re: What dP for my air filter change [Re: dnewton3] #5165035 07/19/19 08:08 AM
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FlyNavyP3 Offline
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I would probably change at or about 10" of restriction over a new filter tested at WOT. I've never been able to perceive a difference in performance with an additional 10" of restriction. In your case that would be 21" so once the gauge trips the 20" notch but before 25" is tripped. In my experience it takes a really long time to build up that much restriction and the filter looks really disgusting at that point.


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Re: What dP for my air filter change [Re: dnewton3] #5165109 07/19/19 09:14 AM
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My mazda has one installed. I emailed wix and they told me on a small gas engine to go to 15 or 16" of HG. My baseline is at about 8" on a fresh flter. I am currently sitting at 11" and has been for a while. The filter has been in place for 45K miles. Ill probably change it when it hits 20" on the gauge.


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Re: What dP for my air filter change [Re: E150GT] #5165238 07/19/19 11:26 AM
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Originally Posted by E150GT
My mazda has one installed. I emailed wix and they told me on a small gas engine to go to 15 or 16" of HG. My baseline is at about 8" on a fresh flter. I am currently sitting at 11" and has been for a while. The filter has been in place for 45K miles. Ill probably change it when it hits 20" on the gauge.


Would be nice if that info were on the box. But I guess it's "proprietary"??

Doesn't the MAP sensor report similar mmHg readings??

Last edited by Mad_Hatter; 07/19/19 11:38 AM.
Re: What dP for my air filter change [Re: Mad_Hatter] #5165286 07/19/19 12:14 PM
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CR94 Offline
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Originally Posted by Mad_Hatter
... Doesn't the MAP sensor report similar mmHg readings??
It's farther downstream, beyond the throttle, where the absolute pressure can be much farther below atmospheric.


2011 Toyota Prius now at 102K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: What dP for my air filter change [Re: CR94] #5165294 07/19/19 12:25 PM
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Originally Posted by CR94
Originally Posted by Mad_Hatter
... Doesn't the MAP sensor report similar mmHg readings??
It's farther downstream, beyond the throttle, where the absolute pressure can be much farther below atmospheric.

Ok, but at WOT is there really that much of a difference between the MAP sensor reading and this gauge? I understand that the pcv vents to the intake but like a small vacuum leak, at WOT a vacuum leak, crankcase gasses or the EGR should have little to no effect on absolute manifold pressure, no?? (I can't think of anything else south of the air filter)

Seems to me that this gauge is more of a convenience item (and there's nothing inherently wrong with that), whereas a trucker wouldn't need to plug in an OBD2 to see if air is being restricted below acceptable levels (mmHg)... they can just pop the hood and get a quick looksie.

Last edited by Mad_Hatter; 07/19/19 12:42 PM.
Re: What dP for my air filter change [Re: dnewton3] #5165592 07/19/19 05:33 PM
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ZeeOSix Offline
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Originally Posted by dnewton3
I installed a Wix 24801 air filter dP gauge on my new 3.5L Duratec Taurus. My (reasonably) new filter exhibits a vacuum of 11" after a couple of WOT runs.
https://www.amazon.com/WIX-Filters-24801-Filter-Service/dp/B0014BI1KA
The product is actually made by Donaldson; the little paper of install instructions references Donaldson by name.
The gauge goes up to 25" and then would indicate a change is due. I'm not sure if the 25" value is sane or not; these are generic and not specific to any application.


I looks like that device measures the pressure drop across the air filter in units of inches of water (in-H2O). This graph shows that these tested filters seem to be pretty loaded and restrictive around the 16-18 in-H20 realm with 350 CFM airflow. If your engine has less max air flow than 350 CFM then the same debris loaded filter will have less restriction. You can calculate the estimated CFM using your engine displacement, max RPM and use a VE of say 85%.

Seem like changing the filter when you see about 18 in-H2O might be better if you're doing a lot of WOT action. If your calculated max engine CFM is less than 350 CFM then it migh be more like a sign of an approaching air filter change required when your delta-p gauge shows around 15 in-H2O.

Air Filter Restriction Delta-P in Inches of Water.JPG
Re: What dP for my air filter change [Re: dnewton3] #5165657 07/19/19 06:24 PM
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Forgot to add ... keep in mind that there will be some slight pressure drop in the intake system even without an air filter installed in the system. It might be a couple of in-H2O. The only way to get a good indication of the air filter's actual pressure drop would be to compare the drop in a brand new filter of the same make to mask what the intake system drop factor is.

Example:
Pressure drop is 2 in-H2O with no filter in the system.
Pressure drop is 4 in-H2O with a new air filter.
Pressure drop is 12 in-H2O with a dirty filter.

The actual pressure drop of the new filter is 4 - 2 = 2 in-H2O.
The actual pressure drop of the dirty filter is 12 - 2 = 10 in-H2O.
The increase in pressure drop due to debris loading is 10 - 2 = 8 in-H2O.

Re: What dP for my air filter change [Re: ZeeOSix] #5165708 07/19/19 07:11 PM
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CR94 Offline
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Originally Posted by ZeeOSix
... You can calculate the estimated CFM using your engine displacement, max RPM and use a VE of say 85%. ...
Except for forced-induction engines. Don't forget to divide by two.


2011 Toyota Prius now at 102K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: What dP for my air filter change [Re: CR94] #5166530 07/20/19 05:52 PM
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Originally Posted by CR94
Originally Posted by ZeeOSix
... You can calculate the estimated CFM using your engine displacement, max RPM and use a VE of say 85%. ...
Except for forced-induction engines. Don't forget to divide by two.
Most OBDII cars will give you a load value. 100% should equal the displacement or close to it. There is an absolute load value too for forced induction and it will go over 100%


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Re: What dP for my air filter change [Re: dnewton3] #5166540 07/20/19 06:04 PM
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dnewton3 Offline OP
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Well my calculated flow would be around 315 cfm at 6k rpm.
I think I'll watch for 15 or 16" vacuum and at least start paying closer attention at that point. Might go as high as 20", but that would be a call I'd have to make as I got closer.
The point of me getting the gauge is to not blindly FCI the air filter at some "30,000 miles" OEM interval. I've always felt that those are wildly indeterminate and a swag on the part of the OEM.
I had 8k miles on the filter (new car) when I installed the gauge; wish I had done it when new, just for the sake of knowing the true OE full flow condition as a base starting point.

Thanks all!


The act of preventative maintenance, in and of itself, is FAR MORE important than brand/grade/base choices among lubes and filters.
- under maintaining something is akin to abuse/neglect; that can kill equipment by shortening the lifespan
- over maintaining something has never been proven to be anything but a waste of time and money
Re: What dP for my air filter change [Re: dnewton3] #5166616 07/20/19 07:21 PM
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CR94 Offline
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Originally Posted by dnewton3
... some "30,000 miles" OEM interval. I've always felt that those are wildly indeterminate and a swag on the part of the OEM. ...
Of course! At best, I suspect they assume near worst-case conditions, 95th percentile or some such.


2011 Toyota Prius now at 102K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: What dP for my air filter change [Re: dnewton3] #5168344 07/22/19 05:45 PM
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I don't think CFM of that particular test is a concern because the size (surface area) of a filter will vary with the size of the engine it's designed for.
I had a restriction gauge on my previous Toyota Matrix.
I'm sure the CFM was way less than 350, and the filter was sized accordingly.
With a new filter the restriction was 7" H2O.
When the restriction reached 11" I changed the filter after 43,000 miles.
I could have gone farther (17"?), but that was far enough for me.


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Re: What dP for my air filter change [Re: circuitsmith] #5179097 08/04/19 08:29 PM
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Just goes to show how far an air filter can really go. With my conditions and mileage I can probably do 4 years. Will make sure though that the filter is holding up physically due to environmental factors. Keeping in mind that the more you play around with the airbox the more contaminants can potentially leech into the engine.

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