Full or Half Full Gas Tank

I really don't notice much if any mileage difference running empty or full on either of my Jeeps. I recently checked my CJ7 fully loaded for camping and got as good as any time I have ever checked, 11 L/100 km. Now running at different speeds....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

M>

IMO, If there was a measurable decrease in fuel used transporting the lesser weight, it would easily be consumed when you slow, stop, restart and accelerate to cruising speed for the additional fuel stop. Steve g.

Here's another economic nugget to chew on. If your rig has fuel injection, every time it sloshes air it shortens the life of the pump. Thats why it's better to keep at least a quarter tank in there. People who always run near empty seem to eat fuel pumps more often, but that's just my experience as a mechanic. Fuel pumps are not cheap.

I consider the weight of fuel when I fill my VW diesel, it gets nearly 50 MPG, and holds 25 gallons with an aux tank. I would spend more hauling fuel in these mountains than I would save buying it at a cheaper station in the valley, 80 miles away. On long trips in flatlands, I fill it up at the cheapest stop, but at home, I only put about ten bucks in it at a time. The

1600 cc engine is a little piss-ant, and I can feel the extra weight.

You guys think too much it just hurts my little brain so my math is easy. Time and measure the distance between home and the gas stop, time and measure the distance between your destination and return, time and measure the distance between your last gas stop. It all equals fun and that is what it's about, so don't sweat the small shit just have fun and it won't give you a headache.

Einstein's equation states that the amount of energy you have is equal to the mass involved times the square of the speed of light. If 1 gram of mass is converted into energy, then to determine how much energy is involved in ergs, you just multiply 1 gram by the speed of light squared, in units of centimeters per second.

Energy in ergs = 1 gram x ( 30,000,000,000.0 cm/sec) x (30,000,000,000.0 cm/sec).

This equals 900,000,000,000,000,000,000.0 ergs of energy.

Now, to convert this into other physical units is a bit awkward but doable. For instance, this is equal to the energy emitted by a 100 watt bulb (producing 100 x 10 million ergs/sec) for:

900,000,000,000,000,000,000.0/(100 x 10,000,000) = 900,000,000,000.0 seconds. Since there are about 30,000,000.0 seconds in a year, this means that a 100 watt bulb running for 30,000 years produces as much energy as 1 gram of matter converted into energy. Or you can think of it as 30,000 hundred-watt bulbs burning for one year - the output from a small town lighting system.

There are other physical units you could use as well. If you don't like watts, you could use horse power. 1 HP = 745 watts, so 1 gram of matter converted into energy equals 1 HP expended for about 30,000/7.45 = 3500 years. If you don't like grams, you could use pounds. 1 pound = 453 grams so

1 pound converted to energy gives you 453 x ( 900,000,000,000,000,000,000.0 ) ergs. If you like BTUs, however, 1 BTU = 1055 Joules or 10.55 billion ergs per second over one second of time. 1 BTU = 100 watts ( 100 joules/sec) x 10.55 seconds. 1 gram converted to energy would then equal an expenditure of 1 BTU for:

900,000,000,000.0 / 10.55 = 9,000,000,000.0 seconds or about 300 years.

You need to get skinney-er friends.

-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51

I've suddenly developed a migraine!!

It's really irrelevant, since IMHO you should always head out into the boonies with a full tank for safety's sake. It will also lower your CG slightly.

John

John Davies TLCA 14732

'96 Lexus LX450 '00 Audi A4 1.8T quattro Spokane WA USA

Logic says the best mileage will come from an empty tank because Empty weighs less. But, Empty has other overhead that makes you want to be sure this state is never reached.

I would fill the tank at every opportunity, and not worry about what the mileage will be as a result of the extra few pounds. If you were gonna worry about this kind of stuff, you would take all of your suitcases out of the back, and buy new clothes at WalMart along the way.

It depends upon the specific gravity of the particular gasoline blend. In general, you can figure on around 6.2 to 6.3 lbs/gallon. If you kept 10 gallons out of the tank you would save around 62 pounds. Not enough to even worry about. You will also be stopping twice as often for fuel. Much better to fill the tank every time.

Dick