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dsq 05-22-2008 04:09 PM

Filling Up Full Tank Adds Unnecessary Weight Thus Reduces Mpg.
 
GAS weighs 8lbs a gallon.
Weight reduces gas mileage.
So i would think it is best to drive with as little gas in the tank as possible.
LEts say you have a 12 gallon tank and fill up to full tank.That fuel weighs 96lbs...If you fill up with only 4 gallons youve just reduced your weight by 64lbs.
Thoughts?

ihatejoefitz 05-22-2008 04:22 PM

There is a point of diminishing returns because of the increased trips to the gas station.

MetroMPG 05-22-2008 04:52 PM

You could fill up, then siphon most of it out and keep it in jerry cans, adding it back to the tank as needed. :)

Sure, weight savings are good. The impact of removing 64 lbs will be very, very small (too small to detect in your fuel consumption log), but it's real.

Also, I thought gas was closer to 6 lbs per US gallon...

PaleMelanesian 05-22-2008 05:06 PM

1 Attachment(s)
Some of you have seen this before, or an earlier copy of it.

This is my daily commute, over the last 1.5 years. 500+ data points.

125% (above full on the gauge) and 1% (empty / low fuel light) both have 1/3 as many data points as the others.

My car stumbles / sputters a bit when it gets low, but still has fuel. I haven't run it dry yet. I may need to fix something there.

I have an 11 gallon tank.

Q3 is the 75th percentile, or halfway from average to max.
Q1 is the 25th, or halfway from average to min.

The linear portion (25%-125%) of the mean chart calculates out to about 0.5% decrease per gallon added.

http://forum.ecomodder.com/attachmen...0&d=1211486767
Attachment 780

dsq 05-22-2008 05:10 PM

yes you are right...it does weigh aprox 6lbs.
I thought it was the same as water.

http://www.santacruzpl.org/readyref/...gasoline.shtml

igo 05-22-2008 05:25 PM

That is a really interesting graph. You average over a 2 mpg increase riding with a 1/4 tank vs. a full tank. It makes sense but, it is cool to see a graph of the mpg.

Just seeing that graph makes me want to do some weight reduction.

ihatejoefitz 05-22-2008 06:03 PM

What can account for the drop from 25% -> 1% ?

PaleMelanesian 05-22-2008 06:15 PM

Updated the post above, but:
My car sputters and really doesn't want to start/restart when it's low. I do a lot more engine-on coasting and leave it running at stops instead of shutting down. There's still fuel available, but there's something it doesn't like. It's probably an issue with my car.

MetroMPG 05-22-2008 10:17 PM

Quote:

Originally Posted by PaleMelanesian (Post 27765)
Some of you have seen this before, or an earlier copy of it.

I hadn't - thanks for reposting.

Quote:

The linear portion (25%-125%) of the mean chart calculates out to about 0.5% decrease per gallon added.
Any theory on why you're seeing such a large gain for such a small weight difference?

PaleMelanesian 05-23-2008 12:06 AM

I don't know. It shouldn't be that large a difference, but there it is. My strategy now is to run it low, but not quite to empty.

I did notice after filling up this morning, my glide points were off - rolling farther from the same starting speed. I do LOTS of P&G, so maybe the weight difference is more relevant there.

I like your idea of siphoning out gallons and then adding them back later. :D


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