HowTo: Maximize Fuel Economy

[3-Wheeler]

I've been thinking about my average fuel consumption graphic here at EcoModder for some time now, and contemplating why the Average is closer to the minimum values, rather than between the Minimum and Maximum values.

You can see in the graphic below that the peak fuel consumption has quite a large gap (blue dots) compared to the much smaller gap for the minimum values (red dots).

I've also emphasized the Average values, and one can easily see that it hugs the lower values.



This got me thinking.... how does one calculate the effective mean data from max and min values?

Let's say that a car gets 70 mpg on one tank and then 130 mpg on the next. Is the average mpg 100?

Let's see.

Using the equation below, one can find out what the effective mpg is when combining 70 mpg and 130 mpg.

The equation is another way of looking at the total fuel consumption similar to grams per hour, rather than miles per gallon. The higher fuel consumption for the 70 mpg tank swamps out the higher mpg tank. This is the jest of the equation when summing fuel consumption.



The equation can be simplified below.



If I did the math correctly, the effective mean fuel consumption is equivalent to 91 mpg, not 100 as I first thought.

This surprised me. And points to an interesting fact.

The easiest way to increase the mean, is to concentrate on the Low values, not the High. For me, this means looking for ways to get better mileage in the Winter, rather than looking for super high numbers in the summer (even though it's fun).

So, if Winter driving is to be maximized, several items float to the top of the list.

Cold air is denser, so this means Aero is large concern. This may seem obvious here at EcoModder, but cold air is about 15% more dense than summer, so a good body shape is important.

Maintaining engine heat is also a big factor. And this includes engine heatup and maintaining heat once the engine is shut off.

An Automatic Radiator Block would almost be a must, as well as a some sort of Engine Blanket or thermal barrier to maintain engine heat.

A Block Heater is also on my ToDo list this summer. I would like to add a 120VAC hookup on the front facia when I do the Auto Grill Block to make plugging-in easier.

Once I get the motorcycle back on the road this year, the topics above will be considered this summer, while it's relatively easy to work on.

Jim.

[mikeyjd]

A block heater improves summer averages too

[ecoTex]

I never looked at it that way. It always surprised me how a bad trip average would seem to exponentially affect my tank average. My brain is overheating.

[ecoTex]

I started messing with the equation to help myself wrap my head around it. We, who use MPG, would like to think a 100 mile trip at 50mpg and a 100 mile trip at 100mpg would net you a 75mpg average. But that is averaging the MILES not the gallons. It should be an average of a 100 mile trip that used 2 gallons and 100 mile trip that used 1 gallon. Which nets a 200 mile trip with 3 gallons used, or 66mpg. Thanks Three wheeler, now I am really going to be upset about bad tanks.

[MetroMPG]

You can see in the graphic below that the peak fuel consumption has quite a large gap (blue dots) compared to the much smaller gap for the minimum values (red dots).

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.

Using L/100 km or gal/100 mi would reveal a much less extreme graph.

[serialk11r]

Harmonic mean. (what you typed)

[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.
If you tank the same amount every time, say 10 galllons, then 130 MPG will get you 1300 miles on a 10 gallon tank and 70 MPG will get you 700 miles on 10 gallon.
That is 2000 miles on 20 gallon so 100 mpg average...

It is actually quite easy to keep tank volume constant; if you have a 15 gallon tank, dirve till it is nearly empty then you can add exactly 10 gallon every time (even though it is not really full).

Or you can just fill it up, enter the receipts in your tank log and not worry about these details...

[101Volts]

So does this mean in a smaller scale that if I put engine heaters in the 1984 Caprice (To have warm starts instead of cold starts,) That will put the MPGs up a noticeable amount? Maybe I should start using the block heater in the Caravan, I found there is one in it that I didn't know about.

[user removed]

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.

[sheepdog 44]

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.

When you have consistent tank fills, everything adds up nicely, but it works that way in only that instance of exact same tank refills. It gets wonky when you try to add two different mpg readings for the same distance (or different distances).

The most common will be trip A to work, and trip B home: Both will be the same distance more or less but averaging the two will get you an inaccurate mpg number. For the same distance, The best you can do is double your worst trip. And even if you got 40mpg trip A uphill, and 1,000mpg trip B downhill, You'd get less than 80mpg combined. Which is why the lowest mpg you get matters so much. Trip B in this case is more or less a ratio between 0 and Infinite mpg of how much you can double trip A.

You need to think this way if your going to mentally calculate average section mpg. Say pulse 10meters(25mpg), coast 10meters(50mpg), coast 10meters coast 10 meters(75mpg).