Gas gage going up and down - Tilted Forum Project Discussion Community

Averett · 06-09-2004, 10:18 AM

Hey car guys (and girls),

I have a 2001 Civic with a little over 36,000 miles on it. 2 weekends ago I noticed I was near empty so I went to fill up. Well, to my shock it only took about $16.00 to fill up. When it normally takes about $21.00 (Stupid gas prices)

So I figured my gas gage must have been off. Before this I had been parked on a hill for about 2 hours. Front end of the car lower than the back. Could this have caused my gage to be so far off?

I've also noticed while driving that my gas will fluctuate. It will be below half a tank left, then a few miles down the road a little bit more than half a tank left. What could be causing this?

Also, my maintenance required light has been flashing, but I know that normally this doesn't mean anything on the Civic, it's set to go off every now and again apparently

Should I be worried the gas gage? Or is this normal?

Thanks in andvance

Also, is gage spelled "gage" or "guage"

Signed,
Car Idiot

onetime2 · 06-09-2004, 10:22 AM

I wouldn't worry about it.

From howstuffworks.com...

http://auto.howstuffworks.com/fuel-gauge.htm

Quote:

How Fuel Gauges Work
by Karim Nice

Introduction to How Fuel Gauges Work
The Sending Unit
The Gauge
Microprocessor-controlled Gauges

If you're like me, you like to squeeze every last mile you can out of your tank of fuel. If you could get 20 miles extra from each tank, that could save you two or three trips to the gas station over the course of a year.

The main impediment to stretching your mileage is the fuel gauge on your car, which makes you think you have less fuel than you actually do. These devices are notoriously inaccurate, showing empty when there are gallons left in the tank and showing full for the first 50 miles.

In this article, we'll learn why our fuel gauges behave the way they do. There are two main parts to a fuel gauge: the sender, which measures the level of fuel in the tank, and the gauge, which displays that level to the driver. First, let's see how a typical sender works.

The Sending Unit
The sending unit is located in the fuel tank of the car. It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large.

In the sending unit, the fuel has to drop below a certain level before the float starts to drop.

When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases.

This mechanism is one reason for the inaccuracy of fuel gauges. You may have noticed how your gauge tends to stay on full for quite a while after filling up. When your tank is full, the float is at its maximum raised position -- its upward movement is limited either by the rod it's connected to or by the top of the tank. This means that the float is submerged, and it won't start to sink until the fuel level drops to almost the bottom of the float. The needle on the gauge won't start to move until the float starts to sink.

Running on Empty
You may be surprised at how much fuel you actually have left when the needle is on empty. To find out, check your owner's manual for the exact volume of your fuel tank. Then, the next time your needle shows empty, find the nearest gas station and fill 'er up. Subtract the number of gallons it takes to fill your tank from the volume stated in the owner's manual, and you'll know just how much farther you can go when the gauge hits empty.

Something similar can happen when the float nears the bottom of the tank. Often, the range of motion does not extend to the very bottom, so the float can reach the bottom of its travel while there is still fuel in the tank. This is why, on most cars, the needle goes below empty and eventually stops moving while there is still gas left in the tank.

Another possible cause of inaccuracy is the shape of the fuel tanks. Fuel tanks on cars today are made from plastic, molded to fit into very tight spaces on the cars. Often, the tank may be shaped to fit around pieces of the car body or frame. This means that when the float reaches the halfway point on the tank, there may be more or less than half of the fuel left in the tank, depending on its shape.

Now let's see how the gauge works.

The Gauge
The gauge is also a simple device. The current from the sender passes through a resistor that either wraps around or is located near a bimetallic strip. The bimetallic strip is hooked up to the needle of the gauge through a linkage.

As resistance increases, less current passes through the heating coil, so the bimetallic strip cools. As the strip cools, it straightens out, pulling the gauge from full to empty.

The bimetallic strip is a piece of metal made by laminating two different types of metal together. The metals that make up the strip expand and contract when they are heated or cooled. Each type of metal has its own particular rate of expansion. The two metals that make up the strip are chosen so that the rates of expansion and contraction are different.

When the strip is heated, one metal expands less than the other, so the strip curves, with the metal that expands more on the outside. This bending action is what moves the needle.

Some newer cars, instead of sending the current directly to the gauge, use a microprocessor that reads the output of the resistor and communicates with the dashboard. These systems actually help improve the accuracy of the gauge. Let's take a look at one of these systems.

Microprocessor-controlled Gauges
Some newer cars have a microprocessor that reads the variable resistor in the tank and communicates that reading to another microprocessor in the dashboard. Carmakers can tinker with the gauge movement a little -- they can compensate for the shape of the tank by comparing the float position to a calibration curve. This curve correlates the position of the float with the volume of fuel left in the tank. This allows the gauge to read more accurately, especially in cars with complicated gas-tank shapes.
Systems like this can also trigger a fuel light that signals when fuel is getting low. Most of these lights come on while there are still a couple of gallons of gas left in the tank, giving you plenty of time to stop for fuel.

The microprocessor can also provide some damping to the needle movement. When you go around a turn, or up a hill, the fuel can slosh to one side of the tank and quickly change the float position. If the needle were to respond quickly to all of these changes, it would be bouncing all over the place. Instead, software calculates a moving average of the last several readings of the float position. This means that changes in needle position occur more slowly. You may have noticed this when filling up your car -- you'll finish filling the tank long before the needle reaches full.

While fuel gauges are far from exact, they err on the conservative side.

For more information on fuel gauges and related topics, check out the links on the next page.

Peryn · 06-09-2004, 10:26 AM

First off, i believe it is spelled "gauge".

Your gas tank has a little floater styrofoam thing in it that is hooked on an arm, to what amounts to a dimmer switch. As the gas level, and subsequently the floater and arm, go up the dimmer switch turns. Instead of getting more light like on a lightbulb, the power goes to your gas gauge, which will move up.

Now if your gauge is in the front or back of the tank, as you face downhill, your gas will, like water, try and stay level. Lets say your floater is in the front of the tank and you face downhill. Now as the gas levels out, teh floater will rise, indicating a falsely high amount of gas.

Another situation has been pretty much dealt with on modern cars has to do with gas sloshing around. If you accelerate pretty good, naturally teh gas will move toward the back of the tank. And when you mash on teh brakes, it will fly forward. So when your driving around town and look at the gauge shortly after taking off at a stoplight, it could be reading low. If you look at it after the brakes, and all the fluid went forward, forcing the floater up, it could read falsely high.

Now, do you have a problem? Im not sure. Dont know much about civics particularly, but most modern cars have some kind of anti-slosh mechanism to keep your gauge from going nuts around town. It could be your car is perfectly normal, but im not positive.

Averett · 06-09-2004, 10:30 AM

Interesting

Thanks for the info. It doesn't go up and down too crazy, just a few clicks here or there.

JStrider · 06-09-2004, 12:32 PM

least yours works

my gauge says empty all the time... people i talked to said its prolly a bad sender and would cost like $400 to fix... not worth it... i just use the tripometer...

Averett · 06-09-2004, 12:55 PM

$400? Ha, yeah, I'm not going to spend $400 for a gas guage.

As if I have $400 to spend!!

Nimisys · 06-09-2004, 06:10 PM

if your still under warranty take it in and let honda figure out there headaches.

first off modern cars have a slosh module that basicly just averages the level readings against time to give a fairly accurate fuel level. thus the reason the guage moves up slowly after filling.
i know for gm and the corvette your slosh module was in two peices, a sending card in the right tank (the tank is spilt around the torque tube with a transfer pump in the left tank and the fuel pump in the right) and the actual software calibration in the BCM. for a while we were updating every corvette with a guage problem with an updated calibration that took care of guages that were off or moved around too much. on occasion we would find one where the sending card was fualty so it got replaced. now thats a 50k flagship car and yours is a commuter vehcile, so i doubt it has seperate sender formt he pump, however i am willing to bet the slosh module calibrations are updatable in ne of the cars computers. it maybe worth your while to call the dalership and talk to one of their drivability techs.

choskins · 06-09-2004, 06:22 PM

Your right about Vettes. I can always tell to the exact mile what I had left when the light went on.

MSD · 06-10-2004, 12:50 AM

Quote:

Originally posted by Peryn
First off, i believe it is spelled "gauge".

Your gas tank has a little floater styrofoam thing in it

I know I'm just being nitpicky here, but styrofoam + gas=goo. It's probably polyurethane.

Quote:

Originally posted by JStrider
least yours works my gauge says empty all the time... people i talked to said its prolly a bad sender and would cost like $400 to fix... not worth it... i just use the tripometer...

Ok, quick word of warning. A gas gauge that fluctuates wildly or freezes at E or F can also be a sign of IMPENDING FUEL PUMP FAILURE. I learned that the hard way.

irseg · 06-10-2004, 02:08 AM

Every car I've ever encountered has a gas gauge that moves around a little. A tank of liquid in a moving vehicle is gonna slosh around. Gas gauges accomodate for that by taking an average reading, but it's not going to be 100% consistent.

rockogre · 06-10-2004, 06:51 AM

Not that this helps your problem much but I drove an old truck for years that had a bad gas gauge. I knew pretty much how far I could go on a tank and just kept checking the odometer instead of the gas gauge. Never did run it out of gas. It got to be as normal to me as using the guage used to be and was a lot more accurate.

BadNick · 06-10-2004, 01:16 PM

I heard a news report on NPR a day or two ago that said some gasoline suppliers in some U.S. States had "unknowingly" delivered gas with way excess (illegally high) sulfur content and that many people who tanked up on it are reporting gas gauge problems because the sulfur is corrosive to the float mechanisms.

JStrider · 06-10-2004, 10:11 PM

Quote:

Originally posted by MrSelfDestruct
Ok, quick word of warning. A gas gauge that fluctuates wildly or freezes at E or F can also be a sign of IMPENDING FUEL PUMP FAILURE. I learned that the hard way. [/B]

... mines been broke since i got it from the original owner... 2 years ago... but i know what its like to be stranded... (tranny died 500 miles from home... and 500 miles from the destination... x_X)

Redlemon · 06-11-2004, 07:22 AM

Quote:

Originally posted by BadNick
I heard a news report on NPR a day or two ago that said some gasoline suppliers in some U.S. States had "unknowingly" delivered gas with way excess (illegally high) sulfur content and that many people who tanked up on it are reporting gas gauge problems because the sulfur is corrosive to the float mechanisms.

Thanks, I hadn't heard about it. Looks like it is Motiva (aka Shell and Texaco), in Florida.

NPR : Suit Targets Shell Gas over Sulfur Contamination
TheHawaiiChannel - Automotive - High-Sulfur Shell Gas Leads To Class-Action Lawsuit

06-09-2004, 10:18 AM	#1 (permalink)
Averett Is In Love Location: I'm workin' on it	Gas gage going up and down Hey car guys (and girls), I have a 2001 Civic with a little over 36,000 miles on it. 2 weekends ago I noticed I was near empty so I went to fill up. Well, to my shock it only took about $16.00 to fill up. When it normally takes about $21.00 (Stupid gas prices) So I figured my gas gage must have been off. Before this I had been parked on a hill for about 2 hours. Front end of the car lower than the back. Could this have caused my gage to be so far off? I've also noticed while driving that my gas will fluctuate. It will be below half a tank left, then a few miles down the road a little bit more than half a tank left. What could be causing this? Also, my maintenance required light has been flashing, but I know that normally this doesn't mean anything on the Civic, it's set to go off every now and again apparently Should I be worried the gas gage? Or is this normal? Thanks in andvance Also, is gage spelled "gage" or "guage" Signed, Car Idiot __________________ Absence is to love what wind is to fire. It extinguishes the small, it enkindles the great.

06-09-2004, 10:26 AM	#3 (permalink)
Peryn Junkie Location: San Diego, CA.	First off, i believe it is spelled "gauge". Your gas tank has a little floater styrofoam thing in it that is hooked on an arm, to what amounts to a dimmer switch. As the gas level, and subsequently the floater and arm, go up the dimmer switch turns. Instead of getting more light like on a lightbulb, the power goes to your gas gauge, which will move up. Now if your gauge is in the front or back of the tank, as you face downhill, your gas will, like water, try and stay level. Lets say your floater is in the front of the tank and you face downhill. Now as the gas levels out, teh floater will rise, indicating a falsely high amount of gas. Another situation has been pretty much dealt with on modern cars has to do with gas sloshing around. If you accelerate pretty good, naturally teh gas will move toward the back of the tank. And when you mash on teh brakes, it will fly forward. So when your driving around town and look at the gauge shortly after taking off at a stoplight, it could be reading low. If you look at it after the brakes, and all the fluid went forward, forcing the floater up, it could read falsely high. Now, do you have a problem? Im not sure. Dont know much about civics particularly, but most modern cars have some kind of anti-slosh mechanism to keep your gauge from going nuts around town. It could be your car is perfectly normal, but im not positive. __________________ Dont cry kid, It's not your fault you suck.

06-09-2004, 10:30 AM	#4 (permalink)
Averett Is In Love Location: I'm workin' on it	Interesting Thanks for the info. It doesn't go up and down too crazy, just a few clicks here or there. __________________ Absence is to love what wind is to fire. It extinguishes the small, it enkindles the great.

06-09-2004, 12:32 PM	#5 (permalink)
JStrider Poo-tee-weet? Location: The Woodlands, TX	least yours works my gauge says empty all the time... people i talked to said its prolly a bad sender and would cost like $400 to fix... not worth it... i just use the tripometer... __________________ -=JStrider=- ~Clatto Verata Nicto

06-09-2004, 12:55 PM	#6 (permalink)
Averett Is In Love Location: I'm workin' on it	$400? Ha, yeah, I'm not going to spend $400 for a gas guage. As if I have $400 to spend!! __________________ Absence is to love what wind is to fire. It extinguishes the small, it enkindles the great.

06-09-2004, 06:10 PM	#7 (permalink)
Nimisys Crazy Location: San Diego	if your still under warranty take it in and let honda figure out there headaches. first off modern cars have a slosh module that basicly just averages the level readings against time to give a fairly accurate fuel level. thus the reason the guage moves up slowly after filling. i know for gm and the corvette your slosh module was in two peices, a sending card in the right tank (the tank is spilt around the torque tube with a transfer pump in the left tank and the fuel pump in the right) and the actual software calibration in the BCM. for a while we were updating every corvette with a guage problem with an updated calibration that took care of guages that were off or moved around too much. on occasion we would find one where the sending card was fualty so it got replaced. now thats a 50k flagship car and yours is a commuter vehcile, so i doubt it has seperate sender formt he pump, however i am willing to bet the slosh module calibrations are updatable in ne of the cars computers. it maybe worth your while to call the dalership and talk to one of their drivability techs.

06-09-2004, 06:22 PM	#8 (permalink)
choskins Psycho Location: Greenville, SC	Your right about Vettes. I can always tell to the exact mile what I had left when the light went on. __________________ "Sometimes a cigar is just a cigar." - Sigmund Freud

06-10-2004, 02:08 AM	#10 (permalink)
irseg Junkie Location: Florida	Every car I've ever encountered has a gas gauge that moves around a little. A tank of liquid in a moving vehicle is gonna slosh around. Gas gauges accomodate for that by taking an average reading, but it's not going to be 100% consistent.

06-10-2004, 06:51 AM	#11 (permalink)
rockogre I aim to misbehave! Location: SW Oklahoma	Not that this helps your problem much but I drove an old truck for years that had a bad gas gauge. I knew pretty much how far I could go on a tank and just kept checking the odometer instead of the gas gauge. Never did run it out of gas. It got to be as normal to me as using the guage used to be and was a lot more accurate. __________________ Only two defining forces have ever offered to die for you, Jesus Christ and the American G. I. One died for your soul, the other for your freedom

06-10-2004, 01:16 PM	#12 (permalink)
BadNick Riding the Ocean Spray Location: S.E. PA in U Sofa	I heard a news report on NPR a day or two ago that said some gasoline suppliers in some U.S. States had "unknowingly" delivered gas with way excess (illegally high) sulfur content and that many people who tanked up on it are reporting gas gauge problems because the sulfur is corrosive to the float mechanisms.