HowTo: Maximize Fuel Economy

[mikeyjd]

Originally Posted by Old Mechanic

For the equasion to be correct the gallons used for each fill must be included, or you can use total miles and total gallons combined.

10 gallons 1300 miles @130 MPG
10 gallons 700 miles @ 70 MPG

2000 miles and 20 gallons is 100 MPG.

Am I missing something?

regards
Mech

edit, oops sorry red devil already covered it, long day today.

32 of you 57 fills are at or above your 47 average, and they further above the average mark than your low tanks are below it.

[3-Wheeler]

Originally Posted by RedDevil

Forgive me if I'm wrong, but what really matters when adding up the MPG's is the number of gallons you put in......

Hey, good point RedDevil. I completely forgot the effect of Miles Run per MPG, and it's affect on the calculation is significant.

Allow me to take another try at this, with appropriate units included for clarity.

Trip #1:

35miles/(70 miles/gallon) = 0.500 gallon used

Trip #2:

35miles/(130 miles/gallon) = 0.269 gallon used

Effective Consumption:

(35miles + 35miles)/(0.500gal + 0.269gal) = 91.03miles/gallon

One can see that the lower MPG reading over an equal or greater distance, predominates higher MPG readings. So it's important to improve lower MPG readings.

It's funny, but I have been focusing on improving mileage when it's warmer outside, rather than colder temps. From the above, one can see that it's more important to improve cold weather driving to save fuel.

My equation in post #1 is a little misleading because it does not consider miles driven as RedDevil pointed out.

_______________

Sometimes it's useful to look at a situation in the extreme, so another example:

Trip 3:

98miles/(18miles/gallon) = 5.44 gallons

Trip 4:
44miles/(130miles/gallon) = 0.338 gallons

Effective Consumption:

(98miles+44miles)/(5.44gal+0.338gal) = 24.58miles/gallon

Originally Posted by MetroMPG

Are we not just seeing the effect of using "MPG" as the measurement? Another example of why it's not an ideal way to talk about fuel consumption.

Good point. The MPG notifier just considers the "final" energy efficiency, and not the number of miles driven in the calculation process.

Jim

[3-Wheeler]

Originally Posted by Old Mechanic

.......
10 gallons 1300 miles @130 MPG
10 gallons 700 miles @ 70 MPG

2000 miles and 20 gallons is 100 MPG.

Am I missing something?......

Hi Mech,

Actually no.

However, the example above shows that to make a 70mpg tank + 130mpg tank = 100mpg overall, it takes almost 2X the number of miles from the 130mpg tank to average 100mpg.

If one considers trips of the same distance, then 70mpg + 130mpg does not equal 100mpg.

This example again emphasizes my point. The lower MPG reading predominates, and it's hard to recover from lower MPG readings by adding in higher MPG readings.

It may not be easy, but it's better to take the lowest MPG readings, and find ways to improve them first.

So the question is: "how do we improve cold weather driving?"

Block heaters?
Engine blankets?
Filling in holes in wheel wells?
Insulation under the hood?
Others?

Jim.

[RedDevil]

Yes, you cannot compare MPG per distance (miles), just per gallon. That's where the PG stands for.
You cannot add up by trip MPG. You can add up per tank MPG, if you keep filling more or less the same amount.

Likewise, if you try to add up the l/100 km readings, you cannot work by the tank fills; then you need constant distance.

Both notations have a dividing part. It comes down to this:
You can only ignore the dividing part if that part is the same for all readings.

What works every time is total all the miles and divide by the total of all gallons, etc.