Does filling gas tank when still half full save money? - Mercedes-Benz Forum

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post #1 of 11 (permalink) Old 01-03-2011, 04:08 PM Thread Starter
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Does filling gas tank when still half full save money?


I am hearing different things on this matter.
If I gas up any car all the time when the tank is half full (Or half empty), am I saving money in the long run opposed to if I let it go down to a 1/4 of a tank or less?

Somebody here has to know for sure.


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post #2 of 11 (permalink) Old 01-03-2011, 04:42 PM
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It depends on if the price of gas is going up or down. The only thing you can count on is that you are wasting time at the gas station.
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post #3 of 11 (permalink) Old 01-03-2011, 04:45 PM
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All other things being equal (including gas prices), you'd save money if you only filled it half-way when it was nearly empty. More gas = more weight, more weight = lower fuel economy.

For the same reason, if you let the car get to near empty before you refill, you'll get better overall fuel economy than if you refill at 1/2 tank.

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post #4 of 11 (permalink) Old 01-03-2011, 05:19 PM
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If you think carrying 1/2 of unused fuel makes sense, why don't you load few bags of sand, or concrete to the trunk?
I am always testing my new cars for the reserve range. My MB diesel makes 70 miles with reserve light on, so I don't hesitate to drive 50 on it. Not only that save me fuel by not carrying unnecessary weight, but allows me to avoid desert stations charging arm and leg, while filling up at discount stations or truck stops.
Quite often on long trips I carry an extra can just to extend the reserve.
The only disadvantage on diesel running dry is long bleeding of air from the fuel line.
W210 with tank mounted high is pretty good on priming the fuel.
ML on other hand has fuel pump higher than the tank bottom and complicated venturi system to suck the fuel from the bottom. When you run it dry -you need over 5 gallons to prime the pump.
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post #5 of 11 (permalink) Old 01-03-2011, 06:10 PM
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Fuel saving

is miniscule based on weight reduction.

But ... It is a lot less expensive to fill from half. Makes a difference to me since I pay cash for fuel. It also offers the freedom to "shop" for fuel if you wish.

You minimize condensation in the tank.
You are also always ready without needing to fuel before a drive.

Those last two points don't have a lot to do with cost but factor into my personal protocol.
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post #6 of 11 (permalink) Old 01-03-2011, 10:52 PM
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There are two half ways to save money.
1. You save some money if you drive with half the seats i.e. remove the back seat, it's putting weight on the car unnecessarily.
2. You save a lot more if you drive half way then walk the second half.
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post #7 of 11 (permalink) Old 01-04-2011, 11:44 AM
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Driving style would make a far bigger difference in fuel economy than any such procedure and is a hell of a lot easier to control. For example by simply timing your stops and slowing rather than having to come to a full stop will save you a noticeable amount of fuel. Do this only at lights, etc., not at stop signs or otherwise where a full stop is required. Avoid sudden jump starts, avoid flooring the gas pedal, or basically drive like there is an egg under the pedal is what I've always heard.


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post #8 of 11 (permalink) Old 01-04-2011, 04:34 PM Thread Starter
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Thanks everyone, I appreciate all the answers.

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post #9 of 11 (permalink) Old 01-04-2011, 05:49 PM
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rocky, mbvis, LA, etc...please note that I was not necessarily saying anyone should do that. I said "all other things being equal". If someone doesn't drive a lot and does all the other things, s/he will get better mileage if they only put in a half tank and refill at a gallon left. It's still nonsensical, but for some they might do it, and the more power to them.

Half a tank of gas is about 75 lbs. Several years back one of the car magazines did an article where they had folks open up their trunks and most were carrying around 50-150 lbs of junk back there, and cleaning out their trunks netted them another small but measurable percentage increase in fuel economy. For most people it's easier to clean out their trunks and drive on properly-inflated tires than to never fill the tank beyond half, but again, if you're looking to maximize...practicality may mean something less.

Weight costs gas, period. (All other things being equal.)
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post #10 of 11 (permalink) Old 01-05-2011, 06:23 AM
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i agree with gregs210, i just recently emptied the trunk of my w123, here are the items a blaupunkt subwoofer , 2 amplifiers, 1 damaged alternator, an extra jack, socket wrench set with metal casing, a container with 5liters of water, im not sure of the weight of all of these but the mpg on my 300d has increased from 5kms to 5.5kms per liter, i also inlfated my tires 32psi, i changed my spare tire from 205 60 14 into a much smaller tire a 185 70 14, and most importantly i never accelerated rapidly, i speed up gradually and top speed is only 40mph
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