How Empty is Empty?

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smj999smj
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Postby smj999smj » Thu May 16, 2013 3:59 pm

I get nervous when that DTE starts flashing "******." I usually keep it between half and full and try not to let it run below 1/4. I like to keep that fuel pump fully submerged with plenty of gas to keep it cool.


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Postby skinny2 » Thu May 16, 2013 4:16 pm

smj999smj wrote:I get nervous when that DTE starts flashing "******." I usually keep it between half and full and try not to let it run below 1/4. I like to keep that fuel pump fully submerged with plenty of gas to keep it cool.
Yeah I used to until I figured out there was still quite a bit of fuel in the tank. I don't know how the tank is setup but I would hope 3 gallons would be adequate to cool the pump. I had a tough time when I first bought this as the tank just seemed very small. I was used to 25 gallon tanks but the trend lately is to go small. I have 36 gallon in my Suburban and it really doesn't get substantially less mpg.....I can usually hit 550+ on a tank real easy.

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Postby Zen_master » Thu May 16, 2013 7:18 pm

doctahjones wrote:in my experience and experiments, i've found i have about 3 gallons from the time the light comes on, and about 2 gallons left once you hit the E line.

only once did i go under the E line. put 19.5 gallons in it that time. that's as close as i ever want to get.
So that's the crux of the issue for me. I feel like the gauge is only functional for 80% or so of the tank. If the gauge was in fact below E you would think filling it up would be a lot closer to the alleged 22 gallons these things are supposed to hold than the 19.5 gal you describe.

Imagine my surprise to read in the owner's manual the R51 has a 22 gallon fuel tank and then the first fillup from 20 miles of driving after the fuel warning light on was not even 18 gallons.

Rather frustrating when the fuel club rewards are limited to a certain number of fillups per month. My hope is that I can figure out when exactly the tank is in fact empty and maximize the fuel discounts by putting more in the tank than 17 or 18 gallons. I'd like to be putting 20-21 in there per fillup.

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Postby Zen_master » Wed May 22, 2013 7:10 pm

Ran the same experiment on yet another tank of fuel. My fuel light came on at 305 miles on the tripometer and I filled up at 323 miles. Ergo, I drove 18 miles with the fuel light on. I'm averaging just over 16 miles to the gallon per the vehicle infocenter but the final 18 miles was a mix of city and rush hour highway so I will be conservative and say the vehicle consumed a gallon and a half from the time the light went on until I filled up.

This time I again topped it off until I could see the fuel in the filler neck and there was no more air to be displaced. The total fillup was 19.039 gallons.

If we assume I consumed a gallon and a half when the light went off we can drop the 19.039 to roughly 17.5 gallons and subtract that from 22. This would imply there is 4.5 gallons in the tank when the fuel light kicks on. If we make the assumption I only consumed one gallon of gas in those 18 miles I drove after the fuel light was triggered this would imply 18 from 22 or 4 gallons in the tank when the light initially comes on.

This seems to mesh fairly well with my post from May 16th that there is somewhere around 4 to 4.5 gallons in the tank when the fuel light is triggered. This would lead us to believe that there is an effective range of approximately 50 miles based on average mpg I see posted on these forums from the time the light first comes on until you're bone dry.

Thoughts? Agree or disagree?

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Postby doctahjones » Wed May 22, 2013 8:27 pm

Zen_master wrote:
Imagine my surprise to read in the owner's manual the R51 has a 22 gallon fuel tank
you sure it was 22?

i thought it was a smidge over 21. too lazy to go down and get my manual at the moment. an intarweb search seems to say 21.1.

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Postby Zen_master » Fri May 31, 2013 3:00 pm

doctahjones wrote:
Zen_master wrote:
Imagine my surprise to read in the owner's manual the R51 has a 22 gallon fuel tank
you sure it was 22?

i thought it was a smidge over 21. too lazy to go down and get my manual at the moment. an intarweb search seems to say 21.1.
Just checked my owner's manual and on page 9-2 it states 21 and 1/8 gallons for capacity with the asterisk disclaimer that the capacities listed in the table are approximate. So it appears you're closer to the correct figure than I was.


To give another update I filled up earlier today and put 18.556 gallons in the Pathfinder. Again, I filled it to the point I could see the fuel and it was not bubbling down the filler neck.

I obtained much better fuel economy this week as I had the week off from work and therefore did not sit in traffic. The fuel light came on at 324.9 miles on the tripometer and I filled up at 336.9 miles on the tripometer.

If we assume I consumed a gallon of fuel from the time the light came on until I filled up this would be about 17.5 gallons consumed from a total capacity of 21.125 gallons. Translation is 3.625 gallons when the fuel light is first triggered.

Granted there are some generous assumptions taking place here. I doubt I burned a full gallon of fuel to go 12 miles. And, I'm rounding off in some cases. A more specific calculation would be about 0.8 gallons were consumed assuming 15mpg. Subtracting 0.8 gal from 18.556 gives 17.756 gallons consumed at the point the fuel light is first triggered. 21.125 gal less 17.756 gal = 3.369 gal in the tank when the light first comes on.

This would probably equate to about a 50 mile range after the fuel warning light is first triggered for most of those reporting fuel economy on these forums.

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Postby domestique » Sun Jun 09, 2013 5:12 pm

Thanks for the findings. I have a 2008 V8 LE and routinely get anywehre from 15-16 MPG.

I always stop filling once the pump shuts off and never try to cram gas in, but when my fuel light comes on the DTE always says around 50 miles left. I don't have the exact numbers but I have never put more then 18.7 gallons in my tank. Like another poster though, I try to not let her get below a quarter tank anymore.... not only for the fuel pump but I live in a very humid climate and want to avoid as much moisture accumilation as possible.

I would be very curious to see how many gallons are left in the tank that the pump wouldn't be able to pick up when the Pathfinder would finally shut off. (Getting flashbacks of Kramer and the Seinfeld episode where he drove the test car to empty).


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