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Fuel Considerations

After reading some posts on high mileage Toyotas, I wanted to write this, and it just got longer and longer.

Let us play with some math, by defining the following definitions:

mpg = miles per gallon (m/g) c = cost per gallon (c/g) m = miles g = gallons t = total cost in fuel

Then the total cost in fuel is: t = m / mpg * c

A vehicle's gas mileage is: mpg = m / g

Let's assume Truck A gets 15 MPG, has been driven for 300,000 miles, and gasoline is a *very* conservative $2 per gallon. Then the total cost of fuel is: t = m / mpg * c = (300,000 miles / 15 MPG * $2 per gallon) = 2 * 300,000 / 15 dollars = $40,000

Now let's do the same with Truck B. Truck B gets 30 MPG, and everything else is the same - it is driven for 300,000 miles and gas is still only $2 per gallon. Now, the total cost of fuel is: t = m / mpg * c = (300,000 miles / 30 MPG * $2 per gallon) = 2 * 300,000 / 30 dollars = $20,000

So, how would a person calculate the fuel mileage for a vehicle? The key is in noticing that fuel mileage is noted in "miles per gallon," or m/g. Start by filling the vehicle's gas tank to the top, drive until the tank is empty, and take note of the miles driven on that trip.

If the vehicle starts at 110,234 miles on the odometer and reads 110,492 miles at the next fill-up, the vehicle has traveled (110,492 miles) - (110,234 miles) = (258 miles).

If the vehicle took 8 gallons of fuel to fill, then the fuel mileage is roughly (258 miles) / (8 gallons) = 32 MPG.

This is not very precise, because people will stop to fill the fuel tank at different levels of "tank emptiness" and the tank is not always filled to the same level of "tank fullness." But, if a log of the fuel mileage calculations is kept every time there is a fuel fill-up, the average MPG can be calculated.

Further, by keeping a MPG log, when the MPG suddenly drops for no known reason, the vehicle is having problems (or the math was wrong)!

A lot of people think they are going to save money by buying a motorcycle, which (on average) get about 40 MPG. Keep in mind that a new motorcycle will cost $10,000 or more (not counting the monthly insurance of $75 or so). If that person's daily driven vehicle gets 15 MPG, then their miles per gallon savings is (40 MPG - 15 MPG = 25 MPG).

How far would someone need to ride a motorcycle getting 25 MPG better to pay off just the cost of the motorcycle?

The calculation for total cost can be worked from the same equation as before, by using Algebra to flip some of the numbers around: (t = m / mpg * c) is the same equation as (m = t * mpg / c)

Using the MPG savings of 25 MPG, we see: m = t * mpg / c = ($10,000 * 25 MPG / $2 per gallon) = 125,000 miles

What does this mean? It says that someone will have to drive a motorcycle for 125,000 miles just to break even with the $10,000 they paid for it. To actually save money, the would have to drive that motorcycle further. Again, that does not include the price of insurance on a motorcycle, which will just add to the pot.

Sometimes, it is interesting to look at the math to see the reality.

So, if someone tells you they bought a motorcycle to save money, look back at them and just laugh, because they probably have not done the math.

Regards, Joe Software Engineer BS in Physics BS in Mathematics

Reply to
jp2express
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OK, so in 2002 I bought an 86 2WD for $1000 with a rebuilt engine, new radiator and water pump from a family member who had an auto repair shop and loved Toyota pickups. In the last four years driving 32,000 miles, I've put four tires on and had a clutch job for a total of another $1000 or so. Then about $250 a year insurance.

So my total "hardware" investment has been $3000 over four years.

I get between 24 and 28 mpg. The truck has 360,000 miles on it. Starts after about a half second. Burns a quart in about

1000 miles.

Hard to get rid of this truck, but I got a Prerunner and am very happy with that.

But the 86 has been just incredible. We use it now just to haul trash to the dump.

This does qualify as a money-saver, correct?

- Bob

Reply to
Bob Lema

I kinda look at it a different way thiese days for bussness usage. I break it down to cost in fuel per mile driven or hour of operation since my commercail use I am more concerned with actual costs rather than just MPG.

----------------- TheSnoMan.com

Reply to
SnoMan

(snipped all the boring stuff)

Why not use a very simple method.

Fill the tank to the top. Drive for whatever amount of miles. Fill up to the top again. See how many gallons you have used and devide the amount of 100Miles you have travelled. This will give you a measurment of Gallons/100Miles.

As long as you refill to the top each time its easy math. This is the way mopst countries are going for OE fuel consumption figures. Here in Australia we use litre per 100kms. I fill up the pickup (We call em Utes!) to the top, drive for 450kms and refill. I fill with 68 litres so therefore:

64 divided by 4.50 gives me 14.22 Litres/100kms.
Reply to
Scotty

Keeping track of MPG is easy. just fill up, let the valve on the pump shut off when filled, write the mileage on the ticket, reset the tripmeter to zero, throw the ticket in the console, every so often, put them in a spread sheet set up to do the calcs.

Mine are as follows, 2007 double cab pre runner:

Tank no.miles gals mpg %highway highway miles city miles

1 253 12.4 20.5 50% 126.5 126.5 2 194.8 8.9 21.8 100% 194.8 0 3 293.3 15.5 18.9 0% 0 293.3 4 145.8 8.0 18.2 0% 0 145.8 5 194.6 10.3 18.9 10% 19.46 175.14 6 187.1 8.6 21.6 90% 168.39 18.71 7 312.1 15.9 19.7 66% 205.986106.114 8 231.7 11.7 19.8 40% 92.68 139.02 9 355.9 18.3 19.4 100% 355.9 0 10 308.2 16.4 18.7 20% 61.64 246.56 11 226.7 11.9 19.0 10% 22.67 204.03 12 303.3 13.7 22.1 90% 272.97 30.33 13 300.2 15.7 19.1 0% 0 300.2 14 300 15.0 20.0 50% 150 150 15 295.3 14.7 20.1 66% 194.898100.402with toneau with air 16 325.6 15.4 21.1 90% 293.04 32.56 with toneau with air 17 368.7 17.6 21.0 90% 331.83 36.87 with toneau with air 18 261.6 11.3 23.2 70% 183.12 78.48 with toneau with air 19 296 15.7 18.8 0% 0 296 with toneau with air 5153.9 257.0 20.1 2673.884 2480.016 52% 48%

Frank

Reply to
Frank Boettcher

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