fuel gauge accuracy

[albumartist]

I haven't had the car long but have noticed that my fuel gauge acts odd. I don't know if it's just the nature of this car, which is why I want to get your opinions.

When I fill the car, the needle sits above the full mark, and hardly moves while driving around town. But once it actually gets inside the marks on the gauge, the gauge meter moves down much faster, even though I haven't changed my driving habits. When the meter gets about 1/8 away from the empty line, the fuel light come on.

I guess I'm not used to having a fuel light because the Miatas don't come with one. But still, should the light be coming on that soon, or should it be closer to the E? Also, how accurate is the fuel gauge in general? When you hit the E mark are you truly driving on fumes, or is there a little room. In the Miata, I could bury the needle in the E before being totally out of gas.

 

[SGT_OKINAWA]

When I fill the car, the needle sits above the full mark, and hardly moves while driving around town.

a) Fuel gage technology has not advanced much in the past 50 years.

b) Its just that extra portion of the fuel tank that IS NOT monitored by the gage. Its like you know how two liter soda bottles curves from about 75% up the top of the bottle? Well pretend the fuel gage is mounted at the 75% mark and that curved part to the FUEL DOOR AND PIPE are extra.

By the way DO NOT FILL YOUR TANK ALL THE WAY TO THE OPENING / FUEL CAP, IT IS BAD MMMMMMMM KAY? DRUGS ARE BAD MMMMM KAY.

But once it actually gets inside the marks on the gauge, the gauge meter moves down much faster, even though I haven't changed my driving habits.

That is normal

When the meter gets about 1/8 away from the empty line, the fuel light come on.

NOT all automotive engineers are born the same, -- Tashi Akinawa-san working in Japan may have been in a bad mood that day and wanted to mess with the consumer and place the gage low in the tank on purpose. j/k but truth is, not all gas tanks and their fuel gages are made the same, youll get used to it over time.

I guess I'm not used to having a fuel light because the Miatas don't come with one.

Foot note, all cars in Japan MUST have a fuel low light, yet child car seats are not mandatory, go figure huh? God I love japan.

Also, how accurate is the fuel gauge in general? When you hit the E mark are you truly driving on fumes,

Nope.

or is there a little room. In the Miata, I could bury the needle in the E before being totally out of gas.

Yup, well on mine anyhow, but Id cary a can of gas, hit the highway and test it ! NO NO, Just Kidding, dont run a fuel injected car out of fuel, I know Urban myth, but why risk it.

Hope that helps

Peace!(rei)

 

[albumartist]

Thanks for the info.

 

[straw10]

I've noticed the same thing as far as the fuel gauge. I've filled right when my light goes on a couple of times and it's right around 12.9-13.1 to fill when this happens. It seems like you have a relatively large amount of fuel left (about 3 gallons) when the light goes on. My needle has been well below E and I haven't run out of fuel yet, or put in more than 15 or 15.1 to fill.

 

[skyhawk]

Its normal. At real full tank, such as when filler nozzle has clicked off, The fuel sensor -- a float attached to a potentiometer is already submerged in fuel. So you can be driving several miles and the gauge will not move down yet because fuel level is still higher than the float.

When gauge approaches 'empty', a point is reach when gauge stops moving down. Which means float is hanging and higher than fuel level. But you can still drive because
fuel is still present at the bottom of the tank.

A meticulous designer can take pains to make the readings accurate.. But I guess there is no big demand for it. We are encouraged to head for the nearest station when the 'empty' light is lit.

 

[raspykart]

as time goes people are thought of as dumber. The fuel light is another indication of this. They have the light coming on sooner than in the past because fuel pumps use the fuel as a means of staying cool. The less often people drive with really low fuel the more likely a fuel pump will last longer... and thus reliability looks good. Far as accuracy goes, I'd say its fairly accurate.

 

[dima_rus]

I would normally drive for two days after the light comes on. I'd say you have another 100km with light on, but I wouldn't recommend to dry your tank like that and suck all the crap in to your engine.
Good thing to do is to fill up once you have a quarter tank left.

Just my 0.02

 

[SGT_OKINAWA]

One more:

A less than 1/4 tank is prone to more evaporation, so I'm told.

Peace!(rei)

 

[bootman]

You should have about 12 liters or three US gallons left when that light comes on.

 

[simonnyc]

As someone already mentioned, my experience has been that the fuel gauge light comes on when the tank is down to ~3 gallons which should give you about 60-70 miles to find a gas station.

 

[Robotazky]

One more:

A less than 1/4 tank is prone to more evaporation, so I'm told.

Peace!(rei)

Simply due to increased agitation. The lower the tank the more you're going to agitate the liquid, thus providing energy as the molecules collide to send them into a gaseous state. I wouldn't worry about how much energy you lose from that happening though.

My MX3 actually has a gauge that does not sit on full for very long at all. It's very accurate. And when it shows empty, it's empty. My 5 on the other hand sits on full for a little while. I've noticed that I can top it off and put 3.5 gallons in when the light comes on. However, for whatever reason, my car has a tendency to spill gas out the *&@# side if I don't pay attention to the sound and stop it before it bubbles up to the handle and shuts the pump off. I hate that because of what gas does to paint. Does that happen to anyone else?

 

[SGT_OKINAWA]

Simply due to increased agitation. The lower the tank the more you're going to agitate the liquid, thus providing energy as the molecules collide to send them into a gaseous state. I wouldn't worry about how much energy you lose from that happening though.

My MX3 actually has a gauge that does not sit on full for very long at all. It's very accurate. And when it shows empty, it's empty. My 5 on the other hand sits on full for a little while. I've noticed that I can top it off and put 3.5 gallons in when the light comes on. However, for whatever reason, my car has a tendency to spill gas out the *&@# side if I don't pay attention to the sound and stop it before it bubbles up to the handle and shuts the pump off. I hate that because of what gas does to paint. Does that happen to anyone else?

The pump should detect back presure as the fuel gets to the top and shut off automatically. That or you're not sticking the gas pump nosel down far enough into the opening.

Yes, gas on the paint is bad, but if you go get some water from the window wash bucket and some paper towel and wash it off right away that helps a ton.

Agree, the agitate the liquid is the cause, but true it's so small who'd notice right?

Peace!(rei)

 

[Robotazky]

The pump should detect back presure as the fuel gets to the top and shut off automatically. That or you're not sticking the gas pump nosel down far enough into the opening.

Yes, gas on the paint is bad, but if you go get some water from the window wash bucket and some paper towel and wash it off right away that helps a ton.

Agree, the agitate the liquid is the cause, but true it's so small who'd notice right?

Peace!(rei)

Believe me SGT, I'm paying close attention and putting the nozzle as far in as possible. It would be nice if the fuel filling area on the 5 was like my Focus where the rubber part around the nozzle fits into the fuel filler compartment so that the overspray would go down the little drain instead of down the side of the car. And I do exactly what you mentioned to get the gas off the car when it happens. My fiancee just sat there and watched half a gallon pouring down the side the other day. I was not happy.(rant)

 

[SGT_OKINAWA]

It would be nice if the fuel filling area on the 5 was like my Focus where the rubber part around the nozzle fits into the fuel filler compartment so that the overspray would go down the little drain instead of down the side of the car.

Mine does, (shady) and not saying you can or should do this, but years ago, I drilled a hole and coated the edges with silicon to prevent rust on my old car, sorta like made my own little drain on my car, yes it ran down the INSIDE of the fender, but hey that car is in tiny chunks of metel now... old Toyota Celica I had.

My fiancee just sat there and watched half a gallon pouring down the side the other day. I was not happy.(rant)

You mean 'Ex'- fiance (boom05) LOL! j/k but I hear ya pal I so hate that, my wife is all like, 'who cares about the car, it gets us to school and back that is all.' (headshake

Peace!(rei)

 

[Robotazky]

Hmm, I may look into modifying the fuel filler compartment to handle overflows.

 

[straw10]

Just went 468.2 miles on a tank....that included about 40-45 while the light was on. Didn't want to push it any more than that...only had a $20 on me, so I didn't fill at the time, so I don't know how close I was to empty...

 

[WhiteStar III]

From experience

Max Fuel capacity - 17.25 gal
Reserve (Low fuel Light) - 2.5 gal
"Overfill" capacity (gal before the needle moves from full) - 3.5 gal

which means just 13.75-14 gal is enough to show a "full" tank (pump shut-off).

 

[KBrian]

Thanks for the specifications, Whitestar III. I hit the low fuel light for the first time tonight with 25 miles to go before a gas station. I didn't know when to expect the dreaded "stumble" that signals the start of the walk of shame .

 

[Bluesideup]

Bringing up an old thread because my gauge seems to work a bit differently. It almost never will indicate actually full. Generally after a fillup it will sit at 7/8s or 3/4 of a tank. Eventually it might show full but it's random.

I've tried topping it off and haven't been able to get the gauge to show correctly. Farthest I've gone on a tank is 380 miles and it took 14 gallons. That was with the needle way below E.

Is there any way to recalibrate the fuel gauge on a Mazda5?