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gas gauge peeve
airing a little here...nothing big...but why do gas gauges stay at full longer then anywhere else?...itll just sit at F for 60miles...:confused: ...then all of a sudden DROP....lol...why dont they make gas gauges accurate? sheesh...theyve been around long enough now...this is why i love digital gismos...our towncar is full of em...and the gas is measured digitally...rather niftydoodle!....
-jonathon |
So that as the system ages, and resistance builds in the wires and the connections, it's still fairly accurate. Besides, the extremes of the gauge are the most inaccurate. If you were to pull the pins on either end of the gauge, the needle would go past them when the tank was completely full/empty.
Take care, ~Chris |
Analog gas gauges use floats in the gas tank. The mystery extra full may be your own doing. Do you squeeze every last drop into your tank at the station? It is possible to get at least one gallon into the tank and nozzle above where the float can go. It is also true that there is gas BELOW where the float can get to.
This may be the issue with your car. That or the float sticks a little bit. Either way, digital gauges guess too. There is nothing more accurate than doing the calulcations manually to figure out about how much gas you should have left. I have had to do this from riding motorcycles and never being able to trust the fuel gauge. I'm also rarely more than a half gallon off what I expect to put into the car. But then I deal with numbers for a living, so I have some advantage.:D |
i just use my trip odometer anyways...always have...cuz i know how many miles i get to a tank :) just seems silly that they dont make it so full is the top and empty is the bottom and it changes with every drop of gas thats burned...you wouldnt even need the F pin then :)
-jonathon |
I think its because when you fill the tank up, the gas levelof course raises the float to the top of the tank. But then the gas level rises even further to where the gas also hits the top of the tank and submerges the float.
Then as you burn the gas off, the gas level has to first fall to the level of the bottom of the float before the float can begin to fall. Until then, the guage reads the same full reading. So the gas level can fall like 1- 3 inches,depending on the size of the float,(I dont remember) before the guage is ever affected. What really annoys me is when my guage sometimes reads half when its really at 1/4. Or worse when it's empty! @#$% gas prices. |
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Jonathon. Deuce is right. the float in the tank only can go so high. after full travel of the float, there is still space above that which gas can be about gallon or two. basically the float stays suspended until it reaches it point were it isnt at its full travel.
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Oddball shapes
As well as the topped out or bottomed out float and the extra gas phenomenon, the tanks themselves are some times shaped strangely. That makes the float fall faster or slower at some levels than at others. That might explain the gas gauge at 1/2 when you really only have 1/4.
Rev |
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An extra nickel?
The gas tank could easily have a "bubble" above and below the float that it could fit into at the extremes. But that would be too simple and might cost an extra nickel. It's also just not too high on the manufacturer's priority list to have an accurate gas gauge.
Rev |
Re: An extra nickel?
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beaten down by "the man", jonathon |
The point that you guys seem to be missing is that when the tank is full, and the needle is pegged, it still has farther to go. If you were to remove the stopping pin at the full mark, the needle would go beyond it, and you would see start to drop right away, as gas was used. It's not that the float design is such that the sender continues to think the tank is full until you use up a gallon or two so that the float moves. The float moves right away.
I learned this in an Automotive Electrical Systems class I took at the local cc when I was preparing for my ASE A6 cert. They had us measure the resistance from the sender. We filled the tank full, and then used the fuel pump to drain out fuel. The resistance started to change before we even had a quart pumped out. Interestingly enough, I am currently trying to advise a gentleman on F150online as to how to set up his gas gauge so that it reads correctly. He removed the needle from the gauge so that he could paint it, when the tank was full. When he pulled the needle off, the shaft it sits on rotated slightly, without him knowing it, so that when he put the needle back on, it read incorrectly. He said he knew right away that something was wrong because the gas gauge started to go down right away, rather than not moving for the usual first 20 miles or so. When the needle got to the empty mark, he filled it, and the 19 gallon tank only took 12 gallons. Anyway, food for thought. :) Take care, ~Chris |
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-jonathon |
I actually fooled with my sending unit in my '66 after replacing it for months getting it the way I wanted it. That meant draining the tank and removing the sending unit each time. A real PITA. No amount of moving the float arm on the rheostat shaft would get it right. I finally shortened the arm that holds the float to make it read over full when it was full and below the "E" when it was bone dry. That may not suit everyone, but that's how I like mine to read. BTW, mine doesn't have stop pins on the gauge face. It will go above the "F" and below the "E".
Rev |
Just to frustrate you. ;)
I don't know for sure. We were taught it was allow for slight differences between vehicles and parts (not all sending units read EXACTLY the same), and to allow for resistance to develop in the circuit. Who knows. Nevermind. :) Take care, ~Chris |
Don't get defensive PKRWUD. I think you are exactly right about that. It couldn't be that my 36 year old wiring and my Taiwanese sending unit have anything to do with the discrepenciies could it? Hee,hee.
Rev |
LOL!!!
I'm fine Rev. I was replying to the post before yours. You type a lot faster than me! :D Take care, ~Chris |
I didn't mean to start an argument..heh...it hasn't quite gotten there yet tho...so thats good :) ...and youre the one who took the courses not me :) so i guess if they want to make those damn gas instruments to fit more cars than not, then yes it will be a little off on most of them, but accurate enough to suit everyones needs...so for our sake...ill drop my peeve...lol...im surrundering *white flag*...hehe....liek i said before anyways..i rely more on my trip odometer than my gauge anyways:cool: :D
-jonathon |
Don't do that
Don't do that jj, you have a good point IMHO. No need for any white flags. These discussions are the "life's blood" of the forums.The explanations that have been offered only seem to substantiate what you've observed about the "tolerances" that are built into the gas gauges.
My opinion is that more money would produce more accurate gauges. Do we want to pay more for better gauges. We certainly do for tachometers don't we? My rambling thoughts. Rev |
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