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Old 05-20-2009, 10:04 AM   #1
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Question Air filters and fuel economy

I am a fleet manager for a car sharing company and our director is suggesting that we change out our air filters more often than recommended to increase our fuel economy. I have talked to several mechanics who say it will make no difference if I switch out before 15,000 miles. Does anyone know if new air filters more often can actually make a difference? Also, any difference in economy between paper aftermarket filters and the dealer specified ones?
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Old 05-20-2009, 10:20 AM   #2
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generally speaking, I would go with manufacturer and mechanic recommendations. that being said, if these vehicles are driven down dirt roads where they ingest large amounts of dirt that cloggs the air filters then you may benefit from a change sooner (I assume this isn't the case).

I would say to see what the air filter looks like just before it is replaced. usually the one being replaced doesn't even look that bad when it is thrown away.

also, on your question about aftermarket filters. these generally help with less restriction which logically makes sense to give you better fuel economy but people that drive with FE in mind hardly ever open the throttle to it's potential anyway. theoretically, you could see a gain from this but I have yet to see anyone that will say that they have gained XX amount of miles per gallon with that change.

I would say to save the $50 or so that you were going to spend on the filter and look into other options. one of which is to purchase a scangauge. the $50 won't buy you this scangauge but it would go towards the price. $170 or there abouts. you can find them here www.scangauge.com or on ebay or just do a search for it. it is a computer that (among other things) has a real time MPG meter built into it. there is a calibration procedure and then you are off.

awareness of your fuel efficiency is the first step in bettering it.

(others may tell you differently but these are my opinions)
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Old 05-20-2009, 10:54 AM   #3
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I would recommend you have the drivers keep mileage logs, distance travelled per gallon of fuel used. Then you can compared them and see who is getting the best mileage, and let that driver treach the others how to drive economically. You could even start a contest between drivers to see who could improve their mileage the most.

When you drive a car for maximum mileage, the air filter would have to be in really bad shape to affect mileage. High mileage driving seldom requires any full throttle high speed operation. I am not saying neglect the air filter, and any off paved road operation will greatly reduce the life expectancy.

Personally I vacuum mine out if they show any signs of contamination, and replace them at the manufacturers recommended interval.

regards
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Old 05-20-2009, 11:55 AM   #4
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I agree with your mechanics. You will not see an increase in fuel economy by replacing filters that aren't clogged.

An easy way to get a slight increase in fuel economy might be to add 5 psi to the tires.
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Old 05-20-2009, 12:11 PM   #5
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i would go ahead and do the sidewall max on the tires, and somehow govner out the speed limit to no higher than 65mph, or tell them not to go over say 63mph
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Old 05-20-2009, 12:25 PM   #6
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If this is a car share company like he says it is they aren't driven by employees and if you tell someone with a rental that they can't drive over 65 they'll come by later in the day and drive by at 85.

These are normal people sharing time with a car. I agree that you won't get increased mileage from changing the filters out. The quoted improvement from changing out an air filter is assuming the filter in the car is completely stuffed, so much that you pull a vacuum in the intake pipe at WOT. This causes higher shifts making less power and wasting fuel having the engine out of its powerband.
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Old 05-20-2009, 01:03 PM   #7
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"theoretically, you could see a gain from this"

Nope, not even theoretically.

The guy is barking up the wrong tree. Tell him to look at this: http://www.fueleconomy.gov/feg/maintain.shtml
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Old 05-20-2009, 01:21 PM   #8
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Quote:
Originally Posted by theclencher View Post
"theoretically, you could see a gain from this"

Nope, not even theoretically.

The guy is barking up the wrong tree. Tell him to look at this: http://www.fueleconomy.gov/feg/maintain.shtml
Nice find. That should be posted as a thread in the "Articles" section. I would have expected a clogged filter to affect MPG, but I can see how it wouldn't, too.
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Old 05-20-2009, 01:41 PM   #9
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I hate it when people say I am wrong


A new study shows that replacing a clogged air filter on cars with fuel-injected, computer-controlled gasoline engines does not improve fuel economy but it can improve acceleration time by around 6 to 11 percent. This kind of engine is prevalent on most gasoline cars manufactured from the early 1980s onward.

Tests suggest that replacing a clogged air filter on an older car with a carbureted engine may improve fuel economy 2 to 6 percent under normal replacement conditions or up to 14 percent if the filter is so clogged that it significantly affects drivability.
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Old 05-20-2009, 01:56 PM   #10
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MAkes sense between EFI and carb. Any vaccum at all in the intake before the carb will cause more fuel to get sucked into the intake.
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