# Saving millions of gallons of oil

Posted By webbie, Jul 3, 2006 at 9:30 PM

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1. #1

### webbie Seasoned Moderator 2. NULL Staff Member

Nov 17, 2005
12,185
1,087
Loc:
Western Mass.
Here's one for the engineers!

While filling the car today, I pondered what the effect would be if every driver only filled their tank 1/2 way instead of full. This would mean each car would be relatively lighter over the road.

Now, this is a difficult calculation, because first someone has to figure out the effect of weight on MPG. Then, they have to figure out how this changes as the car eats gas EITHER from 1/2 to empty, or from full to empty.

But the average might be that the car was 50 lbs lighter during it's daily travels?

2. #2

### HarryBack New Member 2. NULL

Dec 27, 2005
990
1
Loc:
Western Massachusetts
here's another.....everyone loses 20 lbs......how much do they save?

3. #3

### webbie Seasoned Moderator 2. NULL Staff Member

Nov 17, 2005
12,185
1,087
Loc:
Western Mass.
I already thought of that one - it would save a LOT because of all the food saved (produced and transported with oil), let alone the extra weight. However, my idea would be possible to some extent....like asking people to turn off the lights. I have a feeling that my idea would save more than turning off a few light bulbs.

While it might not be good for drivers who do a lot of distance, for me it make no difference whether I fill once every two weeks or fill 1/2 way once a week.

Another advantage - you can do reasonable "fill-ups", so it looks good at the pump to spend only \$20.

As far as doing this with Harrys trucks that haul 10 tons of pellets - well, suffice it to say the savings would be meager.

4. #4

### HarryBack New Member 2. NULL

Dec 27, 2005
990
1
Loc:
Western Massachusetts
14 tons per load....and Ive got two of them.....I could stick with the half tank idea.....tho id have to curtail some of the more distant deliveries, or charge even more exhorbitant delivery charges than i already do!

5. #5

### elkimmeg Guest 2. NULL

the rational is to save fuel and money If fuel cost desend then craig's method works if they rise you loose money
Example being 2 days ago \$2.89 per gallon .If you filled up you are way ahead of the game. Today \$3.03 per gallon
Craig's theory is correct to haul aroung less weight taskes less fuel. The question becomes is it practicle or cost effecient?

6. #6

### saichele Minister of Fire 2. NULL

Nov 18, 2005
542
6
There may be some small savings, but riding with 10 fewer gallons = about 70# savings. out of the 3000+ most cars weigh, it's pretty small.

You also start to run into problems with the tank 'breathing' particularly when you ahve large diurnal temperature swings. The gas expands and contracts a little, but the air does much more so. Leave a car parked with half a tank for too long and you'll get water at the bottom.

Steve

7. #7

### webbie Seasoned Moderator 2. NULL Staff Member

Nov 17, 2005
12,185
1,087
Loc:
Western Mass.
Really rough calcs.
150 million cars in North America
About 60 lbs lighter each = 8 billion lbs lighter.

Assuming 3,000 lbs per car, that would be the equiv. of taking the weight of 2.7 million cars off the road. Assuming these cars used 50 BBls each per year, that is savings of 135 million barrels or about 500+ million gallons.

That is 10 days worth of oil imports....

If nothing else, this shows the wisdom of hybrids and lighter cars with smaller gas tanks. A hybrid with a 10 gallon tank is fine if it gets 50MPG.

8. #8

### saichele Minister of Fire 2. NULL

Nov 18, 2005
542
6
Every generation of a vehicle more gets more bloated -

1996 A4 sedan - 2976
2005 A4 sed - 3252

1992 Explorer 4046
2005 Explorer 4469

1994 civic 4dr 2213
2006 civic 4dr 2690

1994 miata 2264
2006 miata 3078

Let's start by putting less crap in the cars (airbags, power seats, AC, pwr windows, full size spares, IRS, heated seats, etc). Not that they aren't all nice to have, but it makes 60lbs on a half tank scheme kind of minor. Would people be willingto ride in a 1st gen explorer to get 10% better mileage?

Steve

9. #9

### webbie Seasoned Moderator 2. NULL Staff Member

Nov 17, 2005
12,185
1,087
Loc:
Western Mass.
Welll, airbags already saved my son TWICE, so I'm for keeping them!

But your point is well taken. This is where legislation comes in. Manufacturers should pay a penalty or get a credit for each pound above or below what is considered a reasonable weight (say 3,000 lbs).

The government could also limit the size of fuel tanks. This would also lighten the load as well as get manufacturers to up the MPG.

The stuff is actually quite easy - if only they would apply the same rules to cars that they do to many other products.

Stoves, for instance, had to meet a standard called BET - Best Available Technology. Cars should also.

Happy 4th.

10. #10

### cbrodsky Member 2. NULL

Jan 19, 2006
517
0
Loc:
Millbrook, NY
A rough rule-of-thumb is you pick up ~1-2% in gas mileage for each 100 lbs saved. So, you might argue that running 50 lbs lighter on average would give you ~0.75% more fuel efficiency on each tank of gas. For a 15 gallon tank, that's about 33 cents at 3 miles/gallon. If you get 30 miles per gallon, you get about 3.4 miles of extra driving for free on each tank.

That being said, unless you zip right in and out of a gas station, any extra driving you do to refuel midway through that tank eats into the little bit you saved. And even in the simplest in-and-out fuel stop, you still come to a stop, restart, idle a few secs, reaccelarate and get back into traffic which burns some amount of fuel compared to just crusing by and waiting to fill up until you have a full tank. Given the fairly small savings with the lighter load, you may not even come out ahead. A hybrid will do a little better in this regard. (but it's not going to come close to paying for itself

The other big problem is that when you open your tank to fuel, you release quite a bit of unburned fuel into the atmosphere that is often under pressure. This is why many states have vapor recovery systems on the fuel pumps. Every time you build up that pressure in your tank and then crack it to fuel, you're venting off unburned vapors. If you've ever lived in an area with ozone days, one of the actions they take is to avoid fueling during the day because this is a significant pollution source. So I think this would be a serious environmental downside and yet another source of fuel loss.

-Colin