Increasing fuel savings

ANova said:
I got to admit I thought the AC made a bigger difference but it surely can be felt in loss of power.
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That may depend upon the car. I don't notice a difference in mine. But just bear in mind that opening the windows ruins the aerodynamics, and at freeway speeds, aerodynamics are your primary cause of fuel economy loss.
 
RussSchultz said:
Actually, I've found that coasting with the car out of gear improves my gas mileage (ever so slightly). When the transmission isn't engaged, the friction of the engine isn't 'slowing' the car down. Soooo...when I've got a big hill to go down, I take it out of gear and coast.

On my normal commute, it adds about 1mpg for the tank.
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:)

That is exactly what I was saying Russ

In otherwords I thought their gentle braking comment (edmunds) really had to do with having an automatic and it being in 5th gear while you are traveling 20mph so it is essentially as though you are coasting.

What I said was if you take it out of gear coast and press your brakes hard at the end your fuel economy will be the same as if you coasted and gently pressed your brakes...

Anyway you are 100% right I find that coasting does increase fuel economy, but it is not so often that I can do it where I live due to the spacing between lights and the flat ground etc.

edit:
I think that Diesel also has a higher energy release upon combustion, obviously that is the case from a molar standpoint, but I believe from a mass standpoint it is as well due the the fuel being more dense (longer hydrocarbons).
 
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The tests they ran regarding the AC reminds me of that episode of "Mythbusters" where they tested two similar SUV's on a test track to determine whether or not using or not using AC was the most cost efficient.
 
Jim Norton said:
The tests they ran regarding the AC reminds me of that episode of "Mythbusters" where they tested two similar SUV's on a test track to determine whether or not using or not using AC was the most cost efficient.
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Yes, I seem to remember that the car with AC on ran a little bit further, but I think the difference was within the experimental error.
 
Chalnoth said:
Yes, I seem to remember that the car with AC on ran a little bit further, but I think the difference was within the experimental error.
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Indeed. We can now thank them for proving all our parents utterly wrong.
 
Heh, as long as we were in a car that had working AC, my parents always drove with the AC on as temperature demanded.
 
Chalnoth said:
T
Of course, at very high rpm's (set by the size of the valve and cylinder), there will never be enough time to start to fill the cylinder, and the amount of air that makes it into the cylinder will be approximately linear with time allowed (which decreases at higher rpms).
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And at very high RPMs the valves/springs start to oscillate and can crash back into the upward moving piston. Ouch.:devilish:
 
Yes, I seem to remember that the car with AC on ran a little bit further, but I think the difference was within the experimental error.
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If you're referring to the Mythbusters episode, the test was done at 40 mph, and the car without the A/C on ran more than 20% further than the car with A/C on. There was a prior test that involved a computer model that measured the intake vacuum pressure and estimated fuel consumption rate from that which said that the AC did slightly better, but the difference was within experimental error.

When they did it the brute force way -- draining to a set number of gallons and driving at 40 mph until the tank drained, it wasn't even a contest. A/C hurt mileage significantly worse than the drag of having the windows open at that speed.
 
This demands a link:
http://www.tvsquad.com/2005/10/17/mythbusters-mythbusters-revisited/
Last time around, in "AC vs. Windows Down", the MythBusters concluded that using AC was more efficient than opening your windows to cool down. However, they quickly admit that they were wrong to make such a hasty confirmation. In fact, they find that over 50 mph, you're better off with your AC on, but slower than that, open your windows.
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(edited to preserve writer's intent: writer used strikethroughs to indicate a mistake)
 
on my car without A/C, I may open the window but I also may move that slider instead to bring air from the outside :). I guess that plain old aeration is the most fuel efficient, even though it's not the most effective when it's hot.
and when it's 35°C outside and the car was parked under the sun, sure you can think A/C is nice, but driving a few minutes with open windows cools the car considerably.
 
It takes a while for the A/C to really cool the car in hot weather because the amount of air moving isn't that much, so you need to use both -- the open windows while moving in order clear out the hot air and the A/C would only be necessary if further cooling is necessary as the open windows can only be as cool as the outside air.

In fact, they find that over 50 mph, you're better off with your AC on, but slower than that, open your windows.
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I'd also wager that the 50 mph figure is due in part to the fact that they were testing on large SUVs. If the test was done on something smaller and better power:weight ratio, but still much lower total power, and still with a pretty effective A/C, I wouldn't be surprised if that threshold speed is higher.
 
ShootMyMonkey said:
I'd also wager that the 50 mph figure is due in part to the fact that they were testing on large SUVs. If the test was done on something smaller and better power:weight ratio, but still much lower total power, and still with a pretty effective A/C, I wouldn't be surprised if that threshold speed is higher.
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I would typically expect SUV's to have about the highest threshold speed, since their aerodynamics aren't good to begin with. I'd wager that there's going to be much more of a difference to the aerodynamics of a Camaro at 50mph than a Suburban if each opened their windows.
 
RussSchultz said:
Hey! My subaru is pretty sleek. :p
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Well, Subaru SUV's are some of the better ones as far as fuel economy is concerned, and I'm willing to bet that this is largely due to their somewhat better aerodynamics. But the high profile still cannot compare to the aerodynamics of a sedan, or even moreso a sports car.
 
Subaru SUVs are not typical in that they do not have a true frame.


They are like the Rav4, Escape, CRV etc... in that they are really more akin to minivans in construction than trucks. So it is unsuprising that they have better fuel economy.
 
In fact, they find that over 50 mph, you're better off with your AC on, but slower than that, open your windows.
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Whoever told you that should drive a Kia Picanto for the rest of his life. You're never better off with AC, it always draws its power from the engine.
 
_xxx_ said:
Whoever told you that should drive a Kia Picanto for the rest of his life. You're never better off with AC, it always draws its power from the engine.
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Of course it does. But putting the windows down degrades the aerodynamics, which also effectively draws power from the engine. It only stands to reason that as aerodynamics become a more and more dominant factor in fuel consumption (higher speeds), opening the windows becomes worse compared to turning on the AC.
 
Chalnoth said:
Of course it does. But putting the windows down degrades the aerodynamics, which also effectively draws power from the engine. It only stands to reason that as aerodynamics become a more and more dominant factor in fuel consumption (higher speeds), opening the windows becomes worse compared to turning on the AC.
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Oh, ok. I thought it was meant differently, as of AC saving fuel when >50.
 
well I have a question:
if one has to drive several kms with speed which is "a bit fast" for 3rd gear, but a bit low for 4th gear (ie lets say i switch from3rd to 4th at ~ 60km/h), which is the more economic ? 3rd or 4th ? reading previous posts my guess is that driving on 3rd will give more power and ability to accelerate faster, but on 4th less fuel will be used, is this correct ?
 
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