Should you ever change your air filter?

[TFB1]

Originally Posted By: heyu
Originally Posted By: Rolla07
I recently swapped out my reusable Spectre air filter and put in a fram paper element. Never noticed any difference before but the mileage on my last tank was much better and the reusable one never had that effect before. It was dirty on one side so clearly it filters well..but if less air is pulled into the engine wont it increase the fuel sent? Maybe im not understanding it right...


There ya go ,It don't take a rocket scientist to put 2 and 2 together that with a computer controlled engine you will lose gas mileage with a aftermarket reusable air filter ---more air flow signals MORE fuel---If you want fuel economy in your daily driver forget K&N


Yeah that makes sense --- NOT...

That free flowing air filter will possibly give better performance at WOT and make little if any difference at partial throttle opening... Assuming you drive the same, the throttle opening would be less(no doubt ever so slightly) to achieve same results... As far as gas mileage it would only decrease if one WOTs continually, in essence a restrictive filter in a MAF EFI system acts as a governor...

Now on a carbed vehicle all this goes out the window, any flow reduction that causes a vacuum increase between the filter and carb will increase the A/F ratio, causing a rich condition and loss of fuel mileage... A clean filter is required with a carb to maintain best performance...

 

[Shannow]

^+1

 

[Olas]

Originally Posted By: TFB1
Originally Posted By: heyu
Originally Posted By: Rolla07
I recently swapped out my reusable Spectre air filter and put in a fram paper element. Never noticed any difference before but the mileage on my last tank was much better and the reusable one never had that effect before. It was dirty on one side so clearly it filters well..but if less air is pulled into the engine wont it increase the fuel sent? Maybe im not understanding it right...


There ya go ,It don't take a rocket scientist to put 2 and 2 together that with a computer controlled engine you will lose gas mileage with a aftermarket reusable air filter ---more air flow signals MORE fuel---If you want fuel economy in your daily driver forget K&N


Re your carbs comment - it depends on the location of the float bowl vent.. if the vents are open to atmosphere but the fuel delivery is behind a dirty filter it will run overly rich..however, if the float bowl vent and the 'throat' or the carb are both behind the filter then how dirty it is shouldnt make any difference because a carb looks at pressure difference between the venturi and the atmosphere (weight of air pressing down on float bowl) to signal how much fuel to meter in..

Yeah that makes sense --- NOT...

That free flowing air filter will possibly give better performance at WOT and make little if any difference at partial throttle opening... Assuming you drive the same, the throttle opening would be less(no doubt ever so slightly) to achieve same results... As far as gas mileage it would only decrease if one WOTs continually, in essence a restrictive filter in a MAF EFI system acts as a governor...

Now on a carbed vehicle all this goes out the window, any flow reduction that causes a vacuum increase between the filter and carb will increase the A/F ratio, causing a rich condition and loss of fuel mileage... A clean filter is required with a carb to maintain best performance...

 

[Shannow]

Not many carbs in the last (say) 40 years vent to the atmosphere outside the confines of their emissions control system...

 

[Olas]

I dont mean PCV venting to atmosphere (which my car does) I'm talking about the float bowl vent. The float bowl is part of a carburettor, which has to 'see' outside air pressure to be able to meter fuel into the venturi in proportion with airflow.

With a clogged filter and a float bowl vent that sees air in the engine bay, it would run rich - if the float bowl vent is on the clean side of the filter and only sees the same air which has to come through the filter then they both reduce by the same amount over the same time so there would be no effect on mpg

 

[Shannow]

I'm not talking about the PCV valve, I'm talking about what you were talking, the float bowl vent...I've played with a couple...sometimes more than a couple on one engine...(also did my engineering thesis on fuel flow in inlet manifolds, as an aside)

My first couple of cars they vented outside the air cleaner...ain't anything this side of 1970 that vents the float bowl to anywhere other than inside the air cleaner.

Inside the air filter, they will still change the air fuel ratio, as you will be opening the throttle more for a given restriction into the engine...you will be more on the power circuit, less on the idle/off idle, and the density in the carb has changed...

 

[Olas]

I agree that you're opening the throttle more, but fuel is metered in relation to airflow - if less air is passing the idle or main, and you have reduced pressure acting on the surface of the fuel (both due to a plugged filter) then you'll still see enough pressure differential to make the fuel flow out of the jet but it is reduced, proportioonally, because of the reduction in airflow.
I haven't done a thesis on it, and I'm not saying I know more than you, but;
if a plugged filter reduces airflow and fuel is metered in proportion to airflow, surely the mpg would increase?

 

[Bamaro]

The premise is a bit extreme but many people change their air filters way too soon

 

[heyu]

Originally Posted By: Jim Allen
There is a direct connection between WOT power and the airflow capability of the intake system, of which the filter is a part. Many times, it's the plumbing that is the limiting factor, not the filter. Sometimes it's the filter but you don't know until you flowbench the system and dyno test. I did flow bench the system on my F150 and it picked up an inconsequential 12 CFM with the stock MC filter element removed from the stock system (633.99 vs 621.58 CFM). With the snorkel & silencer removed it picked up a more consequential 56 CFM (though dyno testing shows this does not increase power without further tuning). Most stock systems can make the airflow a stock engine needs to make rated power, plus a little extra airflow to account for dirt loading, but that isn't universally true. You have to test individually to know.

As to fuel economy, within-the-limits restriction makes little difference in everyday driving. I would refer you to the air filter vs fuel economy test referenced by nickolas84 above at Air Filters vs Fuel Economy. A restrictive filter makes a substantial difference for WOT fuel economy (open loop operation for EFI systems at WOT) but that only matters to race teams. For the average engine operated in everyday "commuter mode" (closed loop) ... the referenced tests, and other information, shows any MPG differences would be inconsequential, if they existed at all.


I don't need a dyno or a air flow bench for any theories , I did my own testing on a very fuel efficient vehicle and came up 2 miles a gallon less with a reusable air filter ,So ANY MPG differences exist very well in my in the vehicle testing

 

[Jim Allen]

Originally Posted By: heyu


I don't need a dyno or a air flow bench for any theories , I did my own testing on a very fuel efficient vehicle and came up 2 miles a gallon less with a reusable air filter ,So ANY MPG differences exist very well in my in the vehicle testing


MPG measured how and over what period of time? If you did it the way most people do, it doesn't mean much because there are so many variables.

 

[Garak]

Agreed. 2 mpg calculated during normal usage of a vehicle could be well within the error bars, let alone throwing in things like winter versus summer blends.

 

[widman]

The best thing is the restriction gauge. Put the small hole normally 18mm, with the drill bit turning backwards in the plastic intake. It should not be in a curve, doesn't matter what angle.

 

[Ken2]

The filter may deteriorate with heat and age and come apart. Bad problem.

Dirt particles do work their way through filters over a long time. I've changed many that are dirty on the downstream side.

Restriction gauges work best on a diesel due to their lack of a throttle, and even then the engine needs to be running hard with the turbocharger pulling a lot of air in. On a gasoline engine you'd need to watch the gauge during a full throttle, high rpm run.

 

[artificialist]

The gaskets have a limited life, decay, and let unfiltered air through. I encounter it often.

 

[MuzzleFlash40]

I change mine once a year, They cost $6 at walmart. I know they could go longer but I feel better doing it my way.

 

[afoulk]

what about the newer style filters that are made out of a compressed cotton guaze looking material that use the actual filter material to seal the filter to the housing? Do you guys think these can be run longer? I can't imagine the seal would break down over time as long as you don't keep opening up the air cleaner housing to check it.

 

[JOD]

Originally Posted By: Ken2
The filter may deteriorate with heat and age and come apart. Bad problem.

Dirt particles do work their way through filters over a long time. I've changed many that are dirty on the downstream side.

Restriction gauges work best on a diesel due to their lack of a throttle, and even then the engine needs to be running hard with the turbocharger pulling a lot of air in. On a gasoline engine you'd need to watch the gauge during a full throttle, high rpm run.


I think you may be unfamiliar with how restriction gauges actually work. They don't reset themselves, they stay at the highest level of restriction encountered, unless you manually reset that gauge. So, all you have to do to check max restriction is to look at it.

My own experience certainly runs counter to yours. After roughly 60K miles, the clean side on my filter looked like new, and the dirty side was, well, dirty. I do think if you're doing a long filter change interval, it should be appropriate to your conditions and one should use a good-quality filter with good construction. The gasket on mine after 3.5 years was practically like new--but my weather conditions probably play a part.

 

[y_p_w]

Originally Posted By: Voltmaster
It is true that most of these air filters last much longer than we imagine, but really if one drives alot it makes sense to grab a reuseble one. Alot of them offer better filteration from day one because of the oil material.

Not the gauze type. Even K&N claims that the efficience gets better as the load up, with the trapped particles becoming an extension of the filtering surface as the oil transfers.

An oiled paper filter might be about as efficient new as when loaded up. I think another issue is that the oil does inevitably vaporize off. The ones I've removed look like they've dried up.

 

[y_p_w]

I've probably changed the OEM oiled paper filters on my WRX more often than needed. Because of the oiling, the dirt loading pattern is very apparent. The dirt tends to clump on the edges and close to the edges. You can see exactly where the airflow is by this pattern. Only maybe a third of the filter ever gets any substantial dirt.

I think there's probably been a lot of life left when I changed it, but sometimes I just like doing something rather than just leaving it in there.

 

[SteveSRT8]

My car in my sig is kin to a Hoover vacuum. The factory cold air intake is right down perilously close to the road. This results in a lot of crud in the airbox in certain conditions.

The filter still needs little attention as it is carefully located at the highest point and has a substantially sized plenum area beneath it. Notably, without tuning an aftermarket air intake does nuttin' for a 6.1 except make more racket...