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Discussion Starter #1
So... first my qx80 said **** miles to zero.
48995


Of course the fuel gauge is at empty and we know there are still several gallons left. So, I checked out the fuel level and mi to zero in Obdfusion.
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22 miles to zero, but 3 gallons left, which would be about 45 miles according to math.

The reason for wanting to find more accuracy is for those 2nd gen owners that tow. Another 45 miles could be really important on a 1500 mi trip. I'll update this when I fill up to see the different between what it says I have in gal and what I actually had.
 

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You don't want to repeatedly run your tank down to nearly empty. The fuel pump is cooled by the fuel around it. Not good to be running it without cooling.

Besides, my wife has to stop every 150-200 miles to go pee anyway.

Keith
 
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this is nothing new.




the cars gauge is conservative on purpose. cant agree more with what camp stated.
 

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Discussion Starter #4
Uh huh. I saw, % in there but I'm curious if the obd gauge in gal remaining is correct/accurate.

Also, I regularly run without the fuel pump submerged in a variety of vehicles. None of which fail.

Best practice? No, but not catastrophic.
 

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i dont think anyone stated it would fail - its just not wise to continue doing it because its a fact the pump uses the petrol to keep it cool. you may never see an issue with it in your lifetime of owing the car. do what you do. :)
 

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Discussion Starter #6
So, at least for the second gen, the obd fuel meter is also not correct.
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Says 1.5 gal left but only filled up with ...

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So I suppose I could go down to zero and still have to gallons left. Anyone tried to bend the in tank float?
 

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lol,
your findings have been talked about for years on this forum. ive gone down to the red in the qx and after filling up i had at least 5 more gallons.
 

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I don't think it rest flat at the bottom so we would never really get to 0. Also the fuel tank is large so a gallon might not even raise its level to an inch higher.
 

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Discussion Starter #9
lol,
your findings have been talked about for years on this forum. ive gone down to the red in the qx and after filling up i had at least 5 more gallons.
Well the other thread said the obd WAS accurate. It is not. It's off by 2 gallons. If it's exactly two gallons I'll take that as a useful piece on info. I tow in areas in Nevada, Utah, and Nebraska where fill ups can be sorta planned depending on various MPG, but sometimes I really need to know really how many miles to zero and being **** at 60 miles to zero but it really means 100 miles can make a difference is some areas.
 

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my point is this - the tank has a few more gallons than what will be registered on the obd AND the gauge. this is due to the float not being able to register all the petrol in the tank. the petrol sloshes around and that always alters the remaining gallons left.

i get you want to know the EXACT gallons left. we all do. im sure others also travel with toy haulers, trailers, family, etc in remote areas and every bit helps. with modern gps now you can pinpoint a petrol station easily, so you can pre plan your trip better so you are not worrying about is it 100 miles left or 10 miles left.
 

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You don't want to repeatedly run your tank down to nearly empty. The fuel pump is cooled by the fuel around it. Not good to be running it without cooling.

Besides, my wife has to stop every 150-200 miles to go pee anyway.

Keith
This is one of the biggest in inaccuracies regarding operation of a pump. This may have applied for cars back in the day but not high capacity modern fuel pumps. IT's not ever wise to run your tank completely empty but as long as their is fuel available to prime the fuel pump, it will not increase the chance of it failing due to the levels in the fuel tank as long as it's not empy. What actually cools the pump is the actual pumping it self, not the submergence. The Volume flow is what extracts heat from the actual pump operation. Gasoline in liquid form doesn't have the best thermal conductivity and specific heat to ever be a great conductor of heat as a standalone liquid. In contrast, your typical coolant mixture (ethyl glycol) is nearly double across the board in terms of cooling capabilities which is why it's considered a great coolant. But even your Glycol in your coolant system has to be transport via a fuel pump to be effective in removing heat. Any mechanic telling you this needs to get into the 21st century.
 

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My Dad convinced my Mom that gas throws up trash into the injectors if you go below half a tank. He's been gone 17 years now and she still heads right to the gas station the second the needle goes vertical. I generally just go whenever it gets below a quarter tank left. The wife, on the other hand, seems to take it as a personal challenge to see how low she can take her Altima towards zero before she gets nervous and gives in. I'm trying to break her of that, but I'm thinking only getting stranded on the side of the road will do it. <sigh>
 
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Funny how these stories get started....my Mom won't fill the car up with gas if the station is receiving a load of fuel from a tanker. Dad told her that when they fill the tanks, it stirs up all the contaminants in the bottom of the tank, and then you'll get a bad tank of fuel.

Keith
 
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