Filling Up Full Tank Adds Unnecessary Weight Thus Reduces Mpg.

[MetroMPG]

You may be on to something with the P&G angle.

After seeing what you've seen, are you motivated to do further weight reduction?

Believe me, if I could easily do the siphon trick on my car, I would. (I've tried, but the filler pipe has a bend in it that confounded my attempts.)

[Dust]

remember that fuel pumps are cooled by fuel. If there isn’t anything to cool it off, it may burn up. Also, if your car has a return fuel line, the fuel being sent back will be heated too.

[bennelson]

Next thing you know, people will be swapping out for SMALLER gas tanks!!!

Seriously though, if you have a car that gets 100 MPG, who needs anything bigger than, say, a three gallon tank?

Motorcycles only carry a couple gallons, and many don't even have a fuel gauge.

[IndyIan]

I'm not arguing about your results but isn't there some benefit to extra mass for pulse and gliding?
Or really mass vs. wind resistance, especially if you have a rolling hills commute? or a powerful engine?
I guess what I'm trying to say is that you could use your cars mass plus a hill to create a flywheel effect. You are storing gravitational energy going up and releasing it going down increasing your glide distance and velocity.

For my commute I haven't really changed my average speed very much hypermiling, but by pulse and gliding with the hills I have improved my mileage by 1/6th.

I would try adding weight to my Neon but it rides near the bumpstops as is. My tracker is so underpowered that adding weight would force me to downshift on many hills probably erasing any benefits of better gliding.
Ian

[PaleMelanesian]

I do notice longer glides when it's full compared to empty. But I think the losses along the way more than equal the gliding gains. It takes more engine output to accelerate the higher mass, and the engine, as we know, is nothing close to efficient.

I think....

[RH77]

I'm generally concerned about evaporate pollution from filling-up too often. We get quite a few "Ozone Alert" days in the Summer, so we know it's a problem. I let it get close to E and completely refill. Better for FE tracking too.

On my last tank (a near best 41.6) I had a passenger for 50 of those miles. For my car, the average adult weighs more than a full tank, so there has to be something to momentum with my driving style (it was mostly highway driving, which, from what I've observed, is benefited by extra weight).

RH77

[chrislk1986]

I think by the time you start getting lower on gas, you try and milk it for whatever you can. I know when I get to 1/2 tank I'll put a lot more effort into driving efficient.

But I've also heard there may be something to do with surface tension or the surface area of the gas. I'll ask my friend where he got that info. Anyone else heard of that?

Chris

[slopemeno]

Competiton sailplanes use water ballast to improve their penetration, however the L/D (lift-vs-drag) remains more or less fixed. In sailplanes the main reason you now see uber-slick planes is that the cleaner planes can escape sink faster than the "gas-bag" floater.

I agree the coast-down angle should be investigated, but I would think in any practical use, the reality of start-stop driving would negate any advantage to increased weight.

And yeah, if you got 100 mpg, you could go with a 2-3 gallon tank, and then you could carry less fuel, then you could use that space for more storage, or reduce the overall size of the car, thus reducing more weight, etc.

[trikkonceptz]

Theoretically I agree with your results, but I have a question. How can you keep accurate mileage by not filing it up? Sure you can control the amount of fuel you put in, but unless you have a digital gauge that displays remaining fuel accurately how can you consistently measure the amount of fuel you used to calculate mpg's?

[jjackstone]

Trik..,
As long as you keep track of how much gas you put in the tank and how many miles you have driven, you can get a relatively accurate mpg reading over time. Say maybe 1000-2000 miles. I agree it would be more difficult for each "tankful". That is what the ScanGuage can be used for.
JJ