Mileage Experiments

[hyuan]

Before I begin, I just wanted to state that I know very little about how cars operate. I'm a software engineer who doesn't do "hardware."

Having said that, I've always noticed that the car seemed "smoother" on a full tank of gas. I wasn't sure if this was because the car was heavier or perhaps with a full tank the car was somehow more efficient.

Thus I began a series of gas mileage experiments.

For the last 3 fillups, I've been filling up after 7-8 gallons have been consumed:

Here's the data:
<pre>
Miles Gallons Miles/Gallon
187.4 8.06 23.25
175.4 7.87 22.28
159.3 6.675 23.87
</pre>

My historical data excluding these three runs is (this is the average of the last 23 data points):

<pre>
Miles Gallons Miles/Gallon
304.4 14.04 21.67
</pre>

I need to take more data for this to be a statistically significant sample. However, the numbers surprise me.

I would think that hauling around more weight would decrease my gas mileage so the trend would be just the opposite?

Do engines operate more efficiently with a full tank?

[This message has been edited by hyuan (edited 11 August 2002).]

 

[Jimbo]

Engines should not operate more efficiently with a full tank. Your assumption that gas mileage should be less with a full tank (or more weight) is correct.

There must be another explanation.

-Jim

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1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
http://homepage.mac.com/jimanders/PhotoAlbum1.html

 

[milz50]

Could the explanation simply be that you are driving more conservatively (consciously or subconsciously) because of your knowledge of the experiment?

 

[hyuan]

Originally posted by milz50:
Could the explanation simply be that you are driving more conservatively (consciously or subconsciously) because of your knowledge of the experiment?

I don't really think so. Although, it is a possibility. My routes are also fairly routine. I've not done anything out of the ordinary as the car is my primary.

 

[Lud]

You need a much larger data set.

 

[gheba_nsx]

I never said this publicly but I also noticed my NSX (no, to be precise both my NSXs) run "better" with a full tank.
The car was more responsive IMO...

 

[nsxtasy]

I've noticed that I get 2 more mpg whenever I fill up at my local Placebo brand gas station.

 

[Ojas]

Originally posted by nsxtasy:
I've noticed that I get 2 more mpg whenever I fill up at my local Placebo brand gas station.

------------------
ojaspatel.com/nsx

 

[nsx4fun]

Everytime you fill up, the amount of gas in your tank when the pump auto-stops can vary. Depending on the flowrate and the temperature. So comparing one fill up to the next, even if you got the exact same mileage on both fills, you could end up with some variation. And the more you empty your tank, the less varation you should see in your calculations. Then there is also variation in the gas and depending on where you get gas (does it vary), then the amount of energy per gallon can vary. I know that in Sacramento they put more MTBE in the gas than in lower populated counties in Ca and in Oregon. Why do i know this? Because one, it is available info, and 2, on a long trip of virtually all freeway driving with cruise control set. I got 24.5mpg with Sacto gas and 28 to 28.5 mpg with Yreka gas and Oregon gas. The high MTBE content in Sacramento County is robbing me of about 20% fuel economy so the air can be less polluted and the water more polluted. That is, if you believe the government when they say MTBE makes for less air pollution.

Fritz

 

[gheba_nsx]

I knew it sounded strange but after hearing I was not alone I confessed. I really have the feeling (sometime, not always) that after filling up the car is more responsive...

 

[steveny]

Is there any chance of increased evaporation when the tank is less than full?