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mikenmar

Effect of full tank on MPG?

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Can anyone out there come up with an estimate of how much it affects mileage to drive with a full tank of gas, versus a near-empty tank?

 

There must be some effect, but is it totally negligible? Physics majors, where are you?

 

Input data: Say one gallon weighs 2.8 kg. A full tank is 17.5 gallons. Let's compare it with driving with one gallon, so the difference is 16.5 gallons, or about 46 kg.

 

So the question is, what is the effect on mileage of hauling around an extra 46 kg?

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Can anyone out there come up with an estimate of how much it affects mileage to drive with a full tank of gas, versus a near-empty tank?

 

There must be some effect, but is it totally negligible? Physics majors, where are you?

 

Input data: Say one gallon weighs 2.8 kg. A full tank is 17.5 gallons. Let's compare it with driving with one gallon, so the difference is 16.5 gallons, or about 46 kg.

 

So the question is, what is the effect on mileage of hauling around an extra 46 kg?

 

Simple guess: you and your car and full tank of gas ~4,000lbs. With about 100lbs less, you have 2.5% less weight. My guess, 2% (+/- .5%) difference.

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Simple guess: you and your car and full tank of gas ~4,000lbs. With about 100lbs less, you have 2.5% less weight. My guess, 2% (+/- .5%) difference.

 

I thought about that too, but this assumes mileage is in inverse proportion to the mass of the vehicle in a simple linear fashion. That's a good assumption if mileage is inversely proportional to the work done to move the vehicle (since work is proportional to mass), but I don't know enough about the mechanics of the engine to say that's accurate.

 

I guess we really need an engineer here.

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They have to do something with weight. That car is still too heavy.

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They have to do something with weight. That car is still too heavy.

 

Gas weighs about 7lbs per gallon. Or full, would be 120lbs.

Your teenager in the back seat has more effect.

 

Do people really think the car is too heavy for it's size?

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Gas weighs about 7lbs per gallon. Or full, would be 120lbs.

Your teenager in the back seat has more effect.

 

Do people really think the car is too heavy for it's size?

 

I love the fact the car seems to have a heavy feel to it. It feels solid. It holds the road well. I rented a 2009 Fusion last winter and our 2010 FFH feels even more solid.

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I love the fact the car seems to have a heavy feel to it. It feels solid. It holds the road well. I rented a 2009 Fusion last winter and our 2010 FFH feels even more solid.

 

I do too, I understand that lighter cars get better gas mileage, and are better for racing and beating the next to you. But the ride is so much better in a heavier car. There are always trade-offs, but I like the balance achieved in the FFH.

 

But back to topic, I have thought about the effect of a full tank on my overall mpg, so my philosophy is to take advantage of the whole tank for the best overall average mpg. I could operate in the 1/4 tank region if I really wanted to squeak out every .1 of a mpg improvement, but that would be way to inconvenient.

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Reply to smr2112:

 

I was doing a comparison the other week between a 1956 Ford Fairlane and this FFH. The '56 weighed in at 3,600 pounds, and I believe (if I'm not mistaken) that the FFH weighs in at approximately 3,750 pounds, depending on equipment. Also, the FFH is only about 4 inches shorter than the old Taurus, and the '56 Ford is about 4 inches longer... You can check the accuracy (on inaccuracy) of my data, but it's still interesting to compare. The car rides better than the 2009 Lincoln MKS (a VERY disappointing car) that I traded in (from a lease). I am buying this FFH; it's so much better... and only weighs a few hundred pounds less than the MKS.

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Good topic however I'm on the convenience side of things (full tank of gas = weight of one passenger) plus lots of gas keeps the fuel pump fully submerged (thus cool) ((fuel pump is in the gas tank like most other cars?)

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The Owners Guide says 300 lbs. costs 1 mpg. so the effect of 100 lbs. of gas is about 1/3 mpg.

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The Owners Guide says 300 lbs. costs 1 mpg. so the effect of 100 lbs. of gas is about 1/3 mpg.

This I completely disagree with. I drive the same route to work every day. If I drive alone, I get 43-44mpg each way. If I carpool with my two friends (~550lbs total), I get 38-39mpg. That's about 5mpg decrease. Using the thumbrule in the owner's guide, I should have less than a 2mpg drop overall. I've repeated this experiment several times and these numbers are pretty consistent. So, I'd say it's more like 1mpg for every 100lbs.

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Interesting. Do your friends ride with you when it's colder? Do you go a different route to pick them up and stop more times? Fuel flows are so low at 40 mpg. that little things have big effects. Keep us informed.

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Interesting. Do your friends ride with you when it's colder? Do you go a different route to pick them up and stop more times? Fuel flows are so low at 40 mpg. that little things have big effects. Keep us informed.

I take the same route every day and the temperature change between rides is negligible. No changes other than maybe my radio being louder when I'm alone. We all live about 200ft from each other, so there's no stops on the ride.

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They must be fibbing about how much they weigh or maybe you have found the missing "Dark Matter" in the universe.

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They must be fibbing about how much they weigh or maybe you have found the missing "Dark Matter" in the universe.

No...I'm sure of their weight. We're in the Navy and we get weighed all the time to make sure we meet standards.

 

I'd be rich if I had discovered dark matter though :)

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