Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - is it true that a full tank gives better mileage?

trebuchet03 · 09-11-2008, 02:15 PM

1. Bonk - ground temps are very consistent. Yes, it matters moreso to the people selling as their tanks aren't always insulated by the earth

2. Bonk - Fuel tanks pump from the bottom anyway - the place you're fueling from will have a fuel filter (I mean, there's a pump in there - they don't want crap in there).
3. Bonk - fuel is going to evaporate... but 1) Not as fast as you're thinking, 2) If you pump fuel into a 5L space of air, you're displacing 5L. If you displace 2.5L twice as often, you're still displacing the same amount of potential fuel vapors. AND weather or not it goes into a vapor recovery system (fuel pump nozzles with the corrugated plastic thinger) - that same volume of potential fuel vapor is being displaced.

The funny thing about the third myth is that it says you should especially do so when it's warm outside... But that contradicts the first point about only filling up when it's cold

4. Catch22 - mostly bonk. Fill up fast and there's less time for fuel to vaporize. Remember, that the amount that actually vaporizes isn't much to begin with. Personally, I fill up a little slower for pump consistency, it's not that it's metering differently, but the way it determines cutoff is more reliable (as someone else already mentioned)

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Extra weight.... I'm going to say close to, if not already, insignificant.

13 gallon tank (15 gallons, but you fuel up when the low fuel light comes on when there's 2 gallons left)... Lets say 7lb/gal.... So that's 84lbs of fuel... 84 pounds of a 3500lb car + 500 pounds of people (you aren't traveling by yourself are you?) is 1.7% of the gross vehicle weight. So if you only keep a half tank max, that's about 1% of total vehicle weight....

For fuel, Meh, I say. Fuel isn't something you're unnecessarily hauling, like the two bowling balls and assortment of diving weight belts in your trunk.... Spend that extra time to track fuel trends and figure out when it's better to fill up and what fuel economy you need to reach that goal

I mean, we could empty our coolant systems a little to save on weight... Run without washer fluid during bug season, add only the minimum amount of oil and gear lube necessary... Drive without shoes (there's some guy in Japan that does that with his Prius)... Light weight lug nuts anyone?

09-11-2008, 02:15 PM	#24 (permalink)
trebuchet03 MechE Join Date: Dec 2007 Location: Bay Area Posts: 1,151 The Miata - '01 Mazda MX-5 Miata Thanks: 0 Thanked 21 Times in 18 Posts	1. Bonk - ground temps are very consistent. Yes, it matters moreso to the people selling as their tanks aren't always insulated by the earth 2. Bonk - Fuel tanks pump from the bottom anyway - the place you're fueling from will have a fuel filter (I mean, there's a pump in there - they don't want crap in there). 3. Bonk - fuel is going to evaporate... but 1) Not as fast as you're thinking, 2) If you pump fuel into a 5L space of air, you're displacing 5L. If you displace 2.5L twice as often, you're still displacing the same amount of potential fuel vapors. AND weather or not it goes into a vapor recovery system (fuel pump nozzles with the corrugated plastic thinger) - that same volume of potential fuel vapor is being displaced. The funny thing about the third myth is that it says you should especially do so when it's warm outside... But that contradicts the first point about only filling up when it's cold 4. Catch22 - mostly bonk. Fill up fast and there's less time for fuel to vaporize. Remember, that the amount that actually vaporizes isn't much to begin with. Personally, I fill up a little slower for pump consistency, it's not that it's metering differently, but the way it determines cutoff is more reliable (as someone else already mentioned) ------ Extra weight.... I'm going to say close to, if not already, insignificant. 13 gallon tank (15 gallons, but you fuel up when the low fuel light comes on when there's 2 gallons left)... Lets say 7lb/gal.... So that's 84lbs of fuel... 84 pounds of a 3500lb car + 500 pounds of people (you aren't traveling by yourself are you?) is 1.7% of the gross vehicle weight. So if you only keep a half tank max, that's about 1% of total vehicle weight.... For fuel, Meh, I say. Fuel isn't something you're unnecessarily hauling, like the two bowling balls and assortment of diving weight belts in your trunk.... Spend that extra time to track fuel trends and figure out when it's better to fill up and what fuel economy you need to reach that goal I mean, we could empty our coolant systems a little to save on weight... Run without washer fluid during bug season, add only the minimum amount of oil and gear lube necessary... Drive without shoes (there's some guy in Japan that does that with his Prius)... Light weight lug nuts anyone? __________________ Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.