Results anomaly (MPG effects when not on level ground at the gas pump)

[aerohead]

I wanted to share something which came up on my latest trip.
Last year,pulling the trailer,I registered the highest-ever mpg for the T-100 between Colorado Springs,and Trinindad,Colorado.
This trip,I duplicated the same run,and hit basically the same anomaly.
It turns out that the T-100 is sensitive to the levelness of pads at filling stations.The likes of which I could never have imagined.
This year,I indicated 46.5 mpg vs 47.9 mpg for last year.I wasn't suspect so far.
I determined to isolate Raton Pass from the more level portions of travel.
When I topped-off in Raton,after crossing the mountains,I was indicating 63-mpg for that 25-mile portion.I knew that this could only be utter horse----,and looking where I was parked,I could see a definite sideways slope to the pad at the pump.Maybe from frost-heave.Don't know.
Anyway,I pulled the truck out and pulled back in on the opposite side of the pump,where the pad sloped away from the pump,and the tank took another 0.914-gallons to actually fill.
So it appears that the pad at Trinidad sloped toward the pump there,and prevented a complete fill,giving a bogus mpg.
It will be next year at the soonest before I can check things out at Trinidad.
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For future trips I'm going to take along a 4-foot spirit level for the cab of the truck with which to check level.
When I fill,I insert the stem of a 6-inch stainless steel thermometer through the filler neck door and dispense fuel until it comes up the neck to form a meniscus,just short of spilling.I presumed that this would be sufficient to get an accurate top-off.Wrong Phil!
Anyway,I wanted to mention it,as you all may want to check for this on your own vehicle.
Short of wind tunnel data,we're almost totally reliant on mpg data from which to reverse-engineer drag coefficients.It doesn't help when reality doesn't jive with intentions.

[ecomodded]

For a closer to true reading factor the .914 gallon difference

[2000neon]

That is interesting, I have always wondered what kind of effect that might have, and whether or not it's measurable, apparently so. Was this is a really slight slope that you had to look to see? Or something obvious and immediately noticeable? Just trying to get an idea of how much slope makes a difference.

[aerohead]

Originally Posted by ecomodded

For a closer to true reading factor the .914 gallon difference

Yeah,had the tank been full at Trinidad,the 24 miles over the mountain would have worked out at around 18 mpg with the additional 0.914 gallons.But it will require a return trip to the Shell station in Trinidad to figure the discrepancy.
This is why auto makers abandoned road testing in favor of wind tunnels,where they have total control over parameters.

[aerohead]

Originally Posted by 2000neon

That is interesting, I have always wondered what kind of effect that might have, and whether or not it's measurable, apparently so. Was this is a really slight slope that you had to look to see? Or something obvious and immediately noticeable? Just trying to get an idea of how much slope makes a difference.

At Raton it was pretty obvious.Like they had had a killer winter,and entrapped moisture below the concrete froze and heaved up the slab.
None of the other stations were apparently tilted,but that's not to say that they weren't to some degree.
Having a level handy will help reveal some of this funny business.Things are hard enough as it is,without discovering that you can't trust your hard-earned quanta!

[2000neon]

I suppose this would be tough to do, and probably a major pain, but it would probably be interesting to try if you have a gas pump that you consistently use. To try and do one fill up with the vehicle sitting level (both front to back and side to side), and if a certain level of consistency was found, you could use some 2 x 4 wood blocks under one side at a time, with increasing height. It would be tough to get exact data, but based on what you observed, a trend/ correlation would probably appear based on "tilt" (camber?) of the vehicle. Then you could even play with it angled front to back to see if there is some difference.

Or maybe I'm over thinking it.

Also, I'm impressed to see a guy from Texas that understands freeze-thaw It seems most people here in Canada don't get the idea! But they are always the ones who notice the same potholes every year...

[ecomodded]

If you are on the road and need gas , add a measured amount 1-2 or 5 ? gallons with that you can factor the added gallons into your final mpg total once filled at your regular filling pump. Mind you, you have to wait for your average mpg not road specific as aerohead wanted.

[Weather Spotter]

that is why when I want to get a read of a mod based on tank to tank fill, I use the same pump for the before and after tanks.

to be totally sure, you could get out a jack and level the vehicle before filling.

[MetroMPG]

Phil - any desire to put a MPGuino in your Toyota to digitally measure fuel use?

Opens up more testing options when you can get reliable consumption results from much shorter runs.

[redyaris]

What we all may need to do is use the statastitions way out and say that the FE is 97% accurate 19 times out of 20...