Filling Up Full Tank Adds Unnecessary Weight Thus Reduces Mpg.

[The Atomic Ass]

Originally Posted by hal9999

I don’t know if this tip was already suggested but I recommend filling up you gasoline tank only half full. This decreases the weight of your car.

This makes off course only sense if you live near to a fuel station.

Not that good of an idea this time of year in the northern hemisphere. The air contains a lot of moisture, which can lead to water in the gas tank. The savings from the weight lost are not high enough to offset the losses incurred if you get enough water in the tank to make the car undriveable.

[hal9999]

You are correct, but:
1. When is your fuel tank always full ? Moisture will anyway always create after its level sinks.
2. There are additives that, at least depending the brand, claim to bind the water and burn it and also clean the injectors. You can use these once at the spring.

[hal9999]

Sorry, I just discovered that this tip was already suggested.
Read:
http://ecomodder.com/forum/showthrea...thus-2487.html
http://ecomodder.com/forum/showthrea...eage-5052.html

[gascort]

the real question is, does the payoff from mpg offset the vapor, mileage, and time losses at the pump when you have to go twice as often? Probably only if you have a big tank. My tank (~44.5 liters) holds less than 45 kg of fuel (see density of gasoline) when absolutely full, so approx. 20 kg average mass reduction by only filling it halfway full doesn't make a huge difference.

[The Atomic Ass]

Originally Posted by hal9999

You are correct, but:
1. When is your fuel tank always full ? Moisture will anyway always create after its level sinks.
2. There are additives that, at least depending the brand, claim to bind the water and burn it and also clean the injectors. You can use these once at the spring.

True, but you condense a disproportionate amount of water from moist air with an empty tank as opposed to a full tank.

Claim, and do, are 2 different things. The additives I've used here have never done anything but ruin fuel economy while leaving water in my tank, and for the most part, are redundant when using good quality gasoline.

[hal9999]

I admit, I don’t know if these additives really work (My mechanic swears that one brand works very well. I tried it but of course couldn’t take a look inside my tank) but the moisture problem mainly appears in the winter and you anyway will have it as soon as your tank level sinks, regardless if you fully filled your tank. But I understand your point that you increase this problem with a half full tank. :-)

To gascort:
I just did a fast calculation for my diesel engine car supposing it would have a lifespan of 150'000 Km and came with a rough result of 4500 Kg. of total mass reduction.
If I didn’t made a mistake I came to ca. 175 Lt. (with my cars fuel consumption values) of fuel economy. Multiply this by millions of cars…

Regarding the problem that you need to go twice as often to the gas station this is correct. In my case I pass every day several gas stations so the extra gas and time consumption is sub-minimal but of course it’s not the same for everyone.

BTW in the << 108 hypermiling / ecodriving tips ...>> of this site it’s stated:

<<4) Clean junk from your trunk
The additional weight you carry in your vehicle doesn't ride for free. It takes energy to move it around. Removing unnecessary stuff from your vehicle saves fuel.>>


But it’s just my 2-cent opinion. :-)

[taco]

yeah that dont work , when u have to fill up every 3 days to work anyways.......
i use about 4.5 gallons of gas a day on my 130ish round trip.

[dichotomous]

Originally Posted by hal9999

You are correct, but:
1. When is your fuel tank always full ? Moisture will anyway always create after its level sinks.
2. There are additives that, at least depending the brand, claim to bind the water and burn it and also clean the injectors. You can use these once at the spring.

1. ever hear your gas tank suck air in when you go to fill up? that's cause there is a vacume, which helps to also reduce the possibility of explosion, it also makes for much less water in the air, if any.

2.the additives cost more than a gallon of gas, and are only about 5-10oz, of isobutyl or methyl alcohal, which is poor to burn in a gasoline engine. basically, since alcohal is hygrophilic, it absorbs water, since the water is now diluted alcohal, it doesnt freeze as well, which allows it to still flow, doesnt burn to well though

trust me, its much better to top off a bunch in the winter than dump a lot of crap in the tank.

[RH77]

I've almost always filled when there is about 1/8 of a tank and have had good results (check my fuel-log). There's a study by Daox floating around here that demonstated optimum FE at different tank levels. The weight could provide more momentum on coasting, while a lighter tank reduces acceleration load. At the least, I prefer the accuracy of filling when near-empty.

Modern vehicles have an on-board vapor recovery system to prevent fuel vapor from evaporating into the atmosphere and creating "Ozone Alert Days" from the fuel creating inhalation hazards. This may be the "sucking sound" experienced. Some municipalities require the same through the fuel pump itself -- basically a return line at the end the spout returns vapor to the station's supply tank. Between fills, fuel-injected vehicles have a return line to send excess fuel back to the fuel tank from the fuel rail. This is over-simplified, but you get the idea.

In conclusion, I would like to see some hard data (at least 3 tests, repeatable) on the water vapor theory. I admit it would be difficult, but possible to establish significance.

RH77

[hal9999]

In conclusion, I would like to see some hard data (at least 3 tests, repeatable) on the water vapor theory. I admit it would be difficult, but possible to establish significance. RH77

I can only agree.