pump errors on small fill-ups

[Matt Timion]

We've all seen it here before. People fill up 1 gallon, or even 2 gallons and they suddenly have 10 more MPG then they've ever had before. Some peope have filled up less than a gallon and have experienced great fuel economy...

Over time the law of averages evens out people's gaslogs, so it isn't much to worry about.

I would like to discuss however how and why this happens. How many gallons must you fill up in order to eliminate this bizarre occurance?

At the suggestion of ThisIsntJared I'm going to make a regression plot to see if there is in fact a correlation between number of gallons filled and gas mileage. I suspect that there will not be one, but it's worth a shot.

[Compaq888]

Filling up less than a gallon is inaccurate. I've tested this diligently.

I think the minimum fill up should be 150 miles.

[kickflipjr]

Yeah I got 50mpg on a 2 gallon fill up. I don't have a scangauge, but i belive it was true or near true. It was straight highway with some drafting. and I had a warm engine to start out.

I have had a few other small fills with accurate (well, not out of the norm)results.
36/39.5/36.7/39.5/33.7

[JanGeo]

gas pump calibration checks are done with a 5 gallon tank so the stations ripping people off have maps on the pumps that pump 5 gallons accurately but more and less gallons short according to a 20/20 show years ago. That's another reason I try to pump 10 gallons.

[GasSavers_DaX]

The only gaslog entries I post are complete fillups. The smallest fillup I have posted is slightly more than 7 US Gallons. Most of mine are 10 to 11 gallons.

[zpiloto]

It would be interesting to see where the cut off is. I had several 3-4 gallon fills when I was testing the affects of weight and vapors on FE with minimun fuel and the MPG's were stable compared to those with 10-12 gallon fills. I think that the biggest problem is there is a lot of short fills after a highway or test run which will give a big increase in the FE over normal anticipated FE.

[rh77]

Originally Posted by zpiloto

It would be interesting to see where the cut off is. I had several 3-4 gallon fills when I was testing the affects of weight and vapors on FE with minimun fuel and the MPG's were stable compared to those with 10-12 gallon fills. I think that the biggest problem is there is a lot of short fills after a highway or test run which will give a big increase in the FE over normal anticipated FE.

I don't usually fuel-up unless theres at least a half-tank gone (6-8 gallons).

With respect to experiments, the last tank was killed by experiments as it was done mid-tank to preserve the "1/2-tank" rule. All in the name of Science! (I guess )

RH77

[ketel0ne]

Full tank fill ups for me and every mile as well, no skips.

[LxMike]

I put in $20 at a time when my low fuel light comes on. $20 gives me about 8-9 gallons of gas. i use that fuel number and the miles i've driven till the next time the low fuel light comes on. i don't do alot of driving and if i did fillup would be a month before i'd need gas again!

[LxMike]

Originally Posted by theclencher

My suggestion would be to request that everyone only submit fill data on 10+ gallon fill-ups. That will help accuracy for any one particular fill-up. Of course over time with fill-up averaging this becomes less critical.

no data from me then... might as well not even be here


guess i'll just lurk here now....