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.

Hmmmm Deuce, just noticing that you are actually only 10 min from me. Im in Mission Viejo off Alicia.

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.

I used to live up there. Until I lived in went away to school. I'm actually picking up my GT from a lady that lives over by Barbardanes park.

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

so im being told :)...i do appreciate the reasoning you guys...now we just have convince ford to build a better float in the tank..lol...they should make it reach the very tip top and the very very bottom...whats the point of submerging a float afterall? maybe a flat ring would work, right? ...im just surprised that they dont actually design a gas tank and float that work together to be the most accurate at a ll gas levels...hrmm...scratch studying physics, ima be an engineer...wee! :p :D

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?
 

you mean they dont care about consumer wants?! *gasp*! i'm rather insulted! :rolleyes: :p :D ...guess thats what a huge corporation will do to ya...*sigh*...

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

so then why dont they change the ratio so the needle moves less and its coordinated to fit the area designed for the gas gauge? this way it would be accurate...i hope you are seeing my point in all of this...lol...cuz i see yours...

-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

Re: Don't do that
 

LOL. Do it the way we do in the Sprint car; with a broom handle that has been notched every 5 gallons. Very accurate, but the car has to be stopped on level ground to check it.

:D

Take care,
~Chris

And that's the way we still do it.........
 

That's how we still do it for engine oil (wet sumps) and auto tranny fluid. Cheap method too, LOL.


Rev

AND...
 

It works ALL THE TIME, 24/7, even without the key!

LOL. Actually, the Sprint car has no electrical system, other than the Mag, so any electrical gauges are out of the question anyway.

:D

Take care,
~Chris

Some things never change.
 

Back in 1958-60 when AJ was racing modifieds ( 1937-39 Chevy's with Offehouser engines) on a 1/4 mile track at Playland Park here in Houston, that's what they had for electrical, a magneto.

Rev

PKRWUD....just out of curiousity...what kind of mustang do you own? i never hear about it, nor have i seen any pics...ure one of the most, if not the most, avid user on this forum, yet all i ever hear about is your little racer :confused: ...are you just a huge ford enthusiast? ive just been kinda wondering...dont take it personally (i hate how online you lose tone and sincerity while talking) because like i said, you are definetly an asset to the site:cool:

-jonathon

I don't own a Mustang. Never have. I work on them all the time, but have never owned one. I first came to this site almost 4 years ago looking for info for a customers Mustang, and I bookmarked the site. A few months later, I checked out the forums, and knew the answers to alot of the questions people were asking, so I joined, and started answering posts. Before long, I found myself stopping by regularly to help out. Been here ever since. I do own my own repair business, and have been ASE certified for 13 or 14 years. I have a pretty good understanding of how things work, and I enjoy helping people who are willing to get dirty. I have also done alot of race work. I crewed for Bill Elliott in '98, and have crewed for two different Sprint car teams the past few years. The team I've been with for the past 2 years is the current champ, and we run a 700 hp N/A small block in a transmissionless 1400 pound (with driver) Sprint car, usually with 6.86:1 rear gears. Racing is my passion. I spent years racing 1/4 mile, but in the past 5 years, I've become more interested in circle track. I have owned several quick cars, from a 521hp Buick to a raced out '64 Ranchero. I also owned a couple of Chevelles, a Trans Am, and a few others. Currently, I have my '95 F150, which is both my work truck and my daily driver. I have an Olds 400 out of a '66 4-4-2 on a stand in my garage, but I haven't decided what I'm going to drop it in when it's finished. I wouldn't mind having another project car, but I haven't found anything that grabs me yet.

Am I a "huge Ford enthusiast"? Not really. I don't favor any specific brand across the board. I think Ford builds the best trucks, I like the Mustang more than anything else in it's category, and I think Ford is leaps and bounds ahead of the competition with their modular engines, but they're far from perfect. I think the 5.0 is faulted in design for a few reasons. Too few head bolts, no firing order that doesn't have sequentially fired cylinders on the same bank, and an oil pump that is mounted away from where the oil goes when you accelerate.

Of my top ten favorite "affordable-when-new" production cars, only 2 or 3 are Fords, but I think that the best quality vehicles being sold today are through the Ford dealerships.

I like most manufacturers, but I seem to have the most experience repairing Fords.

So, do I pass?

:)

Take care,
~Chris

lol...yes you pass :) as i said, you are an asset to this forum...plus i have a soft spot for people who have at least once owned a chevelle :) my dad used to have a 67 ss droptop (true ss btw) 396 with all sorts of stuff done to it (he figures no that it was about a 10 second car)...said nothing could keep up with him (back in the day of street racing camaros and such :) ...course everyone says that...its like a fishing story..hehe) those things can be real mean tho....we even relocated it for him, to see if we could buy it back, but the guy didnt wanna sell :(....but anyways....its too bad youve never owned a mustang...ive grown to love em...id be driving an 88-92 gt right now instead of my 02 if it werent for the fact that i need a car good for 3hours on the highway for those every-other weekend trips home from school...weee :rolleyes: ...but whatever keeps my mom from crying, right? :cool: ...

-jonathon

This compilation pic is the only one I have handy right now that has the '69 SS396 in it. It's a lousy pic, but hey, what can I say. The Pinto below it is one I picked up for $15, and built into the fastest 2000cc Pinto in town, for next to nothing! I just added some parts I had lying around the garage (Holley 460cfm, MSD 6A, etc.), ported the head and the intake, put in a race cam, and a header. Total out of pocket was like $350! It may have been a Pinto, but it was a cool Pinto (1 of 3 I've owned). The truck at the top is my work truck/daily driver. My other Chevelle was a '66 Malibu with a very fast 283/M22. I agree about Chevelles being cool! Chevelles and GTO's are probably my favorites overall.

Take care,
~Chris

http://homepage.mac.com/pkrwud/.Pict...yVehicles.jpeg

Another reason the gauge drops faster as the tank empties is because the sender doesnt actually measure the number of gallons in the tank, but the level the fuel is at. If you look at a mustang tank from the side, it is sort of V shaped, the front is flat, but the rear slopes down. Therefore if the float is near the top of the tank, there would be more gas to burn before the level dropped compared to the bottom of the V.

-----------
|---------| Full
|---------/ 3/4
|--------/ 1/2
|-------/ 1/4
-------- empty


Does that make sense to anyone but me? :D

Tim

Tim-
Do you have any pics of your car? I LOVE that paint job!

Cool!!

Take care,
~Chris

For now, I just have that one pic, but its bigger and a better quality. I believe you can still get it by searching for a post from Mercury titled TimC vs LS1 Transam or something similar. He posted the full size pic there.

Tim