Dirty Air Filters Save Gas
 

Fuel injection apportions fuel based on the amount of air ingested by the engine. The amount that can be ingested is reduced by a dirty air filter, therefore, so is the amount of fuel that will be supplied.

Obama 0 Logic & Reason 1

You need to run for office.

Mileage per fuel unit used would remain unchanged, but due to a decrease in overall total power output potential (aka less total fuel consumption capability) WOT mileage would certainly be improved on a vehicle with a dirty filter.

Me at NAPA Autoparts (Sorry, I meant Pelican Parts)

Me: I need an air filter for my car

Pelican: You want a new or used one?

Me: What's the diff?

Pelican: New are $10/each, used are $12/each

Me: Why would I want a used one for more money?

Pelican: Used ones give you better mileage than new

Me: .....K....

You're not the first one to tell me that!

Move drivers seat way back, then remove shoes and socks, trim toe nails. Same effect?

Optional: Install aforementioned sock over air filter.

Sherwood

Try filling the trunk with dirt and see how that affects mileage. Dirt weighs more than zero, so the added weight in the air filter would cause the car to get poorer mileage (albeit miniscule).

If you want to simulate a dirty air filter, cover 3/4 of it with duct tape, and report back to us in a week with your mileage.

So basically, if you don't put air into the car, you won't use gas. Just think how much you'd save if you didn't put gas in the car......

Yup. that's exactly what they did and mileage is unchanged.

I have a friend who runs a fleet maintenance shop. Pretty high volume. Lots of cars, and LOTS of heavy equipment. He has reviewed the research and is completely convinced that dirty air filters protect engines better than clean ones. Clean ones let larger particles pass through. Dirty ones catch more of the larger particles. Air filters have so much surface area that they can be mostly plugged with dust, and still allow plenty of air though for good engine operation. They keep a close eye on engine operation, intake vacuums, yadda yadda. Dirty filters are better.

So we agree that Obama is a liar and a fool?

Now hold on just a darned minute.
This morning on the radio a jiffy-lube ad said I'd get a 10% increase in mileage if I let them change my air filter.
They also said that if I paid them to change my oil and check the pressure in my tires, along with a new filter I'd get a 15% increase in mileage.
jiffy-lube would never lie to a customer.

Actually the efficiency of an air filter does go up as it get dirtier. I know this from my air pollution control days, but the energy usage to draw air through the filter goes up as well.

ummm what about pumping efficiency?

more restriction on intake = decreased pumping efficiency = decreased thermodynamic efficiency = decreased fuel mileage

Speedy:)

So I guess I should breath through my dirty underwear in order to live longer. Yup, sounds bout right...

Doesn't matter because the AFR stays the same regardless. A clogged filter allows the motor to pump less air, but the puter simply compensates by squirting less fuel.

They've done tests you know. ;)

Why it is true the AFR stays the same (I am not debating that) the pumping efficiency decreases. This in turn decreases the thermodynamic efficiency which in turn decreases the efficiency of the engine (mass flow being equal for "dirty" filter vs. "clean" filter)

Take a garden hose and suck on one end of it while the other end is free of obstruction. Then take your sock, coat it with dirt and mud, tie it on the end of the garden hose and suck on the free end. You will have to "work" harder sucking on the garden hose in scenario II to get the same amount of mass flow. The increased "work" or energy exerted for the same effect will reduce your "sucking" efficiency.

Oh boy this is getting too detailed :)

Speedy:)

Apparently the thermodynamic efficiency doesn't make enough difference to matter. Also, with the intake restricted, the maximum gas usage is reduced.

If the filter is causing restriction at a given throttle position the throttle plate simply opens and negates it. This of course can't happen at WOT which is why maximum potential IS affected.

Take your garden hose example, you error is in assuming there is only one restriction (the sock). The reality is that there would be another valve right by your mouth. Without the sock on the other end you may be able to suck Xcuft of air per second with the mouth valve open 10%. But...with the sock on the other end you need to open the mouth valve to 30% to have the same restriction free flow of Xcuft per second.

Make sense?