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Old 01-02-2011, 01:21 AM   #1
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Just a quick question about how fuelly calculates my mpg

Just a quick question about how fuelly calculates my mpg

Just a quick question about how fuelly calculates my mpg, with my current car i only ever fill it up with 20l at a time and then refill once the fuel light starts flashing at me and always have now would fuelly be calculated my mpg correctly this way if i dont enter it as a partial refil?

dont really want to chuck a full tank in to work it out as it seems too costly
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Old 01-02-2011, 08:16 AM   #2
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Based on how you're adding fuel I don't think Fuelly is going to work for you. Here's more info in the FAQ: Why do I have to fill the tank all the way up every time I buy fuel? and a recent discussion we had about filling up: Why fill my tank?
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Old 01-02-2011, 05:24 PM   #3
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ok thanks funny how shedding weight aids mpg but you all drive around with a full tank
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Old 01-04-2011, 10:43 PM   #4
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If weight was such a direct issue to MPG, then people who are large vs people that are small would have way different MPG ratings.

Honestly I doubt the weight of the fuel has that much of an impact. Up here, especially in winter, you don't want to be running around on a half tank - near empty tank. If you go in the ditch on a late night, you may be there for a while with the engine running to keep warm. Not to mention, if you kept it full, but refilled it at say half tank, it would be the same system you are on now, only this way you would have a buffer for emergencies.

Just my 2 cents. I just think all this filling partway and running it dry is plain, well, stupid to be honest. Don't hate me, but that's how I see it. But to each his/her own I guess.
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Old 01-06-2011, 10:25 AM   #5
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From what I understand reading various automotive magazines and forums, running the fuel that low also doesn't do the fuel injectors any favors. Contaminants that settle to the bottom of the tank are much more likely to get pulled into the system and clog the injectors. Not worth the risk for the little you save on fuel by filling that way. Repairing the fuel injection system on a car will cost more than you saved on fuel.

Better idea might be to put your limited amount of fuel in when the tank hits 1/4 instead of running it as low as you do. You'd still not be carrying the weight of a full tank but it would be better for the car.
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Old 01-06-2011, 08:29 PM   #6
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Think about it logically, the fuel must be drawn off from the bottom of the tank, otehrwise you would run out with gallons left in it !
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Old 01-07-2011, 04:18 AM   #7
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And here we go with the dirt at the bottom of the tank myth again. Nearly all late model cars pull the gas from the bottom of the tank anyway guys, that's how the pump works. And, unless you are fueling during a dust storm, your dirt in the tank is going to be minimal. I recently changed the 212 thousand mile gas tank on my 17yr old Z and guess what? It was practically spotless and dirt free on the inside. I changed it due to bad outer rust, but it had not contaminated the inside. SO, that excuse is not really valid, especially for newer vehicles.

Moral to the story? Just fill it up, and soldier on. Its a lot less painful... LOL
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Old 01-07-2011, 04:23 AM   #8
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I will admit there are some arguments about keeping some fuel in the tank to keep the pump covered and cool. There are some notes about people that ran their tank mostly empty all the time shortening the life of their fuel pump... So there is that to think about too.

Anyways.
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Old 01-07-2011, 07:26 AM   #9
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While all fuel is pulled from the bottom of the tank, overall agitation of the sediment is more likely to occur and be picked up by the system when the fuel level is so low it increases said agitation. Same way as when you pull the plug on a bathtub. Dirt laying at the perimeter of the tub begin moving and increased levels of dirt go down the drain at the end of the draining.

You are absolutely right about the fuel pump cooling and failure.

From http://www.2carpros.com/articles/how-fuel-pump-works

"Some causes of fuel pump failure can include rust or dirt because they can get past the inlet filter sock, which is designed to filter these sediments. When this occurs the fuel pump will break down because of contaminants that have infiltrated the pump and cause it to jam. This will result in having the motor overheat and burn out. Sometimes a fuel pump will not work properly if it is not given the proper amount of fuel needed to run adequately. Your vehicle’s fuel pump relies on fuel running through it to cool and lubricate it. Starving your fuel pump for fuel can cause your vehicle's fuel pump to fail prematurely. Mechanical fuel pumps usually rupture the diaphragm that is used as the pump, and will leak a small amount of fuel externally (from the weep hole) or just not have pressure."
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Old 01-09-2011, 11:38 AM   #10
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Still, said dirt is not going to be happening with a car less than 10 years old, let alone those that are older. Those with cars less than 5 years should NOT be having dirt in the fuel, unless they are leaving their gas caps off all the time and the lid open... I will admit there are some of you out there...

Yeah you, the lady with the big SUV. Stop talking on your cell phone while filling up and make sure you close your tank up properly. (seriously, I watched some woman do exactly that one day. And she got mad at me when I said something about it, imagine that)

Anyway, for those of us that fill up properly, there shouldn't be any dirt issues.

But I still stand by my original statement. Just fill up your tank (if you can afford to) or keep it half-full, rather than empty to half. Its better for you and your car.

Peace and good MPGs!
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