MPG "myths"
- Thread starter ericthepig
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Intesting article, but if you actually read the article, you'll find that some of the things they list as "misconceptions" they actually admit will technically improve gas mileage (although not greatly)... like overinflating your tires and not using the A/C.
Total horse [censored]. Dirty air filter isn't bad for fuel mileage? Whiskey Tango Foxtrot...
So don't bother with a clean air filter let your car work at higher RPMS. And don't follow the owners' manual recommends for premium gas in turbo charged engines. Engine knocking and misfire from running regular gas in turbos isn't a problem? Those toyota, ford, and gm engineers that designed the engines don't know what their talking about.
They forgot to mention you should always aim for 100 MPH on the highway to save time and gas. Try to red line you engine all the time.
Most people already run their cars that way so its not a problem.
Who wrote this article?
They forgot to mention you should always aim for 100 MPH on the highway to save time and gas. Try to red line you engine all the time.
Most people already run their cars that way so its not a problem.
Who wrote this article?
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JHZR2
Staff member
you know it is interesting going to some of the hypermiling websites. Some of their techniques are penny smart and pound foolish to the point of being ridiculous.
Sounds same in the article. One busted turbo engine sure eats away a lot of fuel savings... then again, most folks only keep their cars for 3 years, right?
JMH
Sounds same in the article. One busted turbo engine sure eats away a lot of fuel savings... then again, most folks only keep their cars for 3 years, right?
JMH
I just don't get the air filter comment. I'm sure someone out their will never change their air filter again, because "it doesn't save gas".
It seems like these kinds of articles now appear regularly; and each one is just a rehash of the previous one.
It seems like these kinds of articles now appear regularly; and each one is just a rehash of the previous one.
BTW - I put "myths" in quotes for a reason in the thread title. That one on the airfilter clogging was a choice one. This is likely one of those articles where they just needed something to write about on mpg since it's the topic of the day w/ fuel prices. Yesterday they were probably posting an article on "increasing mpg" - which included - clean air filter, slightly over inflate tires, etc.
Kestas
Staff member
I read what the journalists write on automotive maintenance for entertainment. I remember 20 years ago where they wrote about the dangers of removing your catalytic converter - that it can ruin the engine!
Once I saw CNN my expectations were drastically lowered...
Originally Posted By: Drew99GT
Total horse [censored]. Dirty air filter isn't bad for fuel mileage? Whiskey Tango Foxtrot...
How would it be bad for mileage, assuming it isn't so plugged that the fuel injection system can't maintain the proper mixture?
Total horse [censored]. Dirty air filter isn't bad for fuel mileage? Whiskey Tango Foxtrot...
How would it be bad for mileage, assuming it isn't so plugged that the fuel injection system can't maintain the proper mixture?
re the air filter thing, according to a friend who is a filtration engineer, the vast majority are replaced far too frequently when they still have a long service life left in them.
Of course a lot comes down to the basic design and it's dust holding capacity.
He performed filtration tests to compare various media's, and one of the filters tested was out of one of my vehicles with 20,000km of use.
At the time I lived out in the sticks and drove on dirt roads every day. This filter had significant service life left in it before pressure drop become a factor.
I've also pulled a pre-cleaner out of a mechanically injected diesel farm ute that was so blocked the EPA would've had coniptions if they'd seen the smoke......
Of course a lot comes down to the basic design and it's dust holding capacity.
He performed filtration tests to compare various media's, and one of the filters tested was out of one of my vehicles with 20,000km of use.
At the time I lived out in the sticks and drove on dirt roads every day. This filter had significant service life left in it before pressure drop become a factor.
I've also pulled a pre-cleaner out of a mechanically injected diesel farm ute that was so blocked the EPA would've had coniptions if they'd seen the smoke......
Quote:
While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.
No wonder their information is screwed up, look at their source!
While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.
No wonder their information is screwed up, look at their source!
I'd like to pose a question:
In a modern fuel injected, electronically controlled vehicle. If you take your foot off the gas pedal, the throttle plate closes, there is a higher restriction in the induction system, and therefore less air gets in the engine. The computer compensates by injecting less fuel, in order to maintain a target air-fuel ratio.
This would result in using less gas, yes? Be gentle with the gas pedal, and get more mileage right?
....so, when the air filter is a little bit clogged, isn't that a little bit like driving around with a block of wood under the gas pedal?
...so why would this result in a drop in fuel economy, if you are driving around with a higher restriction in the intake? (kinda like restricting your car to running at 95% throttle or whatever)
Seriously -- why does a clogged filter give LESS mileage??
In a modern fuel injected, electronically controlled vehicle. If you take your foot off the gas pedal, the throttle plate closes, there is a higher restriction in the induction system, and therefore less air gets in the engine. The computer compensates by injecting less fuel, in order to maintain a target air-fuel ratio.
This would result in using less gas, yes? Be gentle with the gas pedal, and get more mileage right?
....so, when the air filter is a little bit clogged, isn't that a little bit like driving around with a block of wood under the gas pedal?
...so why would this result in a drop in fuel economy, if you are driving around with a higher restriction in the intake? (kinda like restricting your car to running at 95% throttle or whatever)
Seriously -- why does a clogged filter give LESS mileage??
Originally Posted By: exranger06
Quote:
While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.
No wonder their information is screwed up, look at their source!
I agree.
Quote:
While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.
No wonder their information is screwed up, look at their source!
I agree.
You can use 87 octane and drive off-boost. Volumetrics depend on amount of charge present. 89 works well in these cars.
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
However, I'm with those questioning the questioners here. I've said before that air filters do NOT need to be replaced as often as most people think. They are designed to provide far in excess of the flow required for normal operation, even after having been used for the appropriate interval. Pressure drop (and consequent changes in volumetric efficiency) will not be a factor of any consequence for fuel efficiency until the filter is well past its manufacturer-recommended lifespan, and in the meantime, actual filtration is improving with every mile.
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
However, I'm with those questioning the questioners here. I've said before that air filters do NOT need to be replaced as often as most people think. They are designed to provide far in excess of the flow required for normal operation, even after having been used for the appropriate interval. Pressure drop (and consequent changes in volumetric efficiency) will not be a factor of any consequence for fuel efficiency until the filter is well past its manufacturer-recommended lifespan, and in the meantime, actual filtration is improving with every mile.
I typically chg my Sienna's OEM air filter every year - it's time for my annual chg, but after reading about air filters here, I think I'll push it out to 1 1/2 to 2 years (we're rarely in dusty conditions, except for the incredible oak pollen season that just ended - have to see it to believe it - you can wash your car, and an hour later it's dusted with green).
The Sienna OEM air filter looks like a pleated blanket - thick plush fabric of some sort. Looks high quality - I hope it is.
Thanks for the info!
The Sienna OEM air filter looks like a pleated blanket - thick plush fabric of some sort. Looks high quality - I hope it is.
Thanks for the info!
Originally Posted By: glennc
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
An extremely plugged filter that the fuel system can't compensate for is another problem, but that is a very dirty filter.
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
An extremely plugged filter that the fuel system can't compensate for is another problem, but that is a very dirty filter.
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Originally Posted By: XS650
Originally Posted By: glennc
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
An extremely plugged filter that the fuel system can't compensate for is another problem, but that is a very dirty filter.
The fuel system isn't meant to "compensate" for a blocked intake tract. Whilst air demands are their lowest at cruise, and your throttle is mostly closed during this time, a VERY plugged filter CAN cause a loss of fuel economy.
The ECM makes a number of assumptions based on things like throttle position and EXPECTS a certain quantity of airflow at a given throttle position depending on engine load. IF the blockage in the air tract is severe enough to actually affect the engine's ability to breathe, then it WILL require more pedal to get the vehicle to sustain the same speed. It WILL require more pedal to accelerate, and in open-loop situations where the values the ECM are using are mostly out of base-table, you WILL go through more fuel.
But, as you've surmised, it would have to be VERY blocked to affect the actual A/F ratio, especially during cruise, since the most air consumption (and fuel consumption) obviously occurs at WOT.
Originally Posted By: glennc
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
An extremely plugged filter that the fuel system can't compensate for is another problem, but that is a very dirty filter.
The fuel system isn't meant to "compensate" for a blocked intake tract. Whilst air demands are their lowest at cruise, and your throttle is mostly closed during this time, a VERY plugged filter CAN cause a loss of fuel economy.
The ECM makes a number of assumptions based on things like throttle position and EXPECTS a certain quantity of airflow at a given throttle position depending on engine load. IF the blockage in the air tract is severe enough to actually affect the engine's ability to breathe, then it WILL require more pedal to get the vehicle to sustain the same speed. It WILL require more pedal to accelerate, and in open-loop situations where the values the ECM are using are mostly out of base-table, you WILL go through more fuel.
But, as you've surmised, it would have to be VERY blocked to affect the actual A/F ratio, especially during cruise, since the most air consumption (and fuel consumption) obviously occurs at WOT.
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Originally Posted By: XS650
Originally Posted By: glennc
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
There is still a pumping loss. You're right, that if it weren't for that loss everything would adjust to compensate, with the throttle at a slightly wider setting. However, any restriction in flow will cause some difference in efficiency, all else equal. The question to me is at what point does that curve approach significance.
Originally Posted By: glennc
Originally Posted By: Test_Drive
Seriously -- why does a clogged filter give LESS mileage??
Because you press the throttle slightly more to compensate.
That doesn't matter. It's still the same amount of air flowing through the engine to deliver the needed power and the closed loop fuel system provides the correct amount of fuel for the air whether the restriction is at the air filter or at the throttle plate.
There is still a pumping loss. You're right, that if it weren't for that loss everything would adjust to compensate, with the throttle at a slightly wider setting. However, any restriction in flow will cause some difference in efficiency, all else equal. The question to me is at what point does that curve approach significance.
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