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BIG discrepancy between tank and MFD - which should I post?

BIG discrepancy between tank and MFD - which should I post?

  #1  
Old 12-01-2006, 01:08 PM
SoopahMan's Avatar
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Default BIG discrepancy between tank and MFD - which should I post?

So, since I always fill up to full I decided it would be worth at least recording the gas put into the Prius each time I fill up instead of being so lazy and using the MFD every time.

What's surprising is that the Prius took in 7.098 gallons of fuel, the Trip Odo showed 423.3mi, and the MFD showed 55.7mpg. 423.3mi/7.098gal is 59.6mpg - a very taunting number since I was shooting for 60mpg with this tank.

I thought MFD numbers were typically overestimating? Is it possible it actually underestimated in this case?

I had 2 notches left on my fuel meter when I filled up with the 7.098gal.
 
  #2  
Old 12-01-2006, 05:08 PM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

Originally Posted by SoopahMan View Post
So, since I always fill up to full I decided it would be worth at least recording the gas put into the Prius each time I fill up instead of being so lazy and using the MFD every time.

What's surprising is that the Prius took in 7.098 gallons of fuel, the Trip Odo showed 423.3mi, and the MFD showed 55.7mpg. 423.3mi/7.098gal is 59.6mpg - a very taunting number since I was shooting for 60mpg with this tank.

I thought MFD numbers were typically overestimating? Is it possible it actually underestimated in this case?

I had 2 notches left on my fuel meter when I filled up with the 7.098gal.
It is the curse of the bladder tank. It turns out that over the long-haul, the tank and pump numbers are the 'gold standard' but any one tank is likely to be off. The MFD is better used for 'testing' and since one clumsy push, it is reset to zero . . .

It really becomes a personal choice. In my case, I write my mileage from one of the trip meters on the receipt and post them all in the database. No individual tank can be treated as 'the answer' but the average turns out to be very nice. I use the MFD for "A" vs "B" tests.

GOOD LUCK!
Bob Wilson
 
  #3  
Old 12-01-2006, 07:06 PM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

SoophahMan,

I use the gallons I pump for the database as that is what I pay for gas. I keep track of the MFD values for comparison. Since my car is new and I was shortfilled by the dealer on my first tank, there is a 8% difference between MFD and hand calcs (in favor of the MFD). It will work itself out. I think others report a 4% or so difference over time.
 
  #4  
Old 12-03-2006, 02:29 AM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

Hmmm - well, I'm sure the tank I'm on now will be abysmal, but I'm gonna switch to the tank method and just keep my own log in my phone of the MFD readings. I originally wanted to avoid that because that's kind of the purpose of the GreenHybrid db, but I find myself writing it down so I can remember it for home anyway.

Thanks for the advice! I also managed to get 80mpg (MFD) over 48 miles of highway yesterday - because they were almost all downhill. Fun to see the number though. Down to 60 now that I climbed back up that highway - so it will be interesting to see how the tank reads out when I fill up.
 
  #5  
Old 12-03-2006, 05:10 PM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

SoopahMan,

80 mpg over 40 miles on the highway; that is great. Don't worry about each tank. I know that it sucks to see a high number on the MFD to only fill up and see your calculated value quite a bit lower. I had one like that, but the next tank, the calculated value was just a little higher than the MFD value. It all works out.
 
  #6  
Old 12-04-2006, 11:16 AM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

I had an odd experience recently with respect to tank readings -- wondering if anyone else had a similar experience. I was down to 1 bar on the tank reading. I went to my parents house, about 10 miles driving. When I left in the evening, I was on the freeway going home when I looked at my bars --- lo and behold there were now FOUR bars showing! I was confused and asked my passenger if she recalled the bars, since she drove the car on the first leg. Her recall was the same as mine.
When we got home we showed three bars.
I got up the next morning, turned on the car, and now only one bar was showing, and it was blinking.
Anyone else have this experience, and if so, what would be a reasonable explanation?
 
  #7  
Old 12-04-2006, 02:18 PM
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Default Re: BIG discrepancy between tank and MFD - which should I post?

I know that in a normal fuel tank with low fuel if you hit a steep hill, the gas can slosh and cause the reading to read out higher than reality. However, with this fuel bladder, perhaps the best answer is gnomes and unicorns.
 
  #8  
Old 12-10-2006, 12:18 PM
fluteman's Avatar
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Default Re: BIG discrepancy between tank and MFD - which should I post?

I can imagine a wrinkled bladder . . . then again I have noidea how they are.
 
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