What makes my gas gauge read differently??

[robl]

Question. I've done some testing with filling up and wanted to know the reasoning why.

I've done 30 fill ups on my tank. 15 have been with Marathon, and 15 with Holiday.

Everytime, my gauge goes to 125 on quarter tank, and 200 when it reaches a half tank, and I end up getting 25-27 MPG...on the Marathon.

However, on the Holiday, I get around 80 miles on a quarter and 125 on a half tank, but still can get about 25, 26 MPG. Any reason why the gas needle would vary this way depending on gas??

 

[jmac]

Stop going by the gauge and go by actual gallons that you put in the tank and miles traveled on the odometer.

If this is what you have been doing, I would say that the Holiday gas has more ethanol + water in it, or is transition gas from the pipeline that is contaminated with other fuels and sold cheaply on the spot market.

 

[glennc]

I think when you fill up at Marathon the filler is pointed uphill and when you fill up at Holiday the filler is pointed downhill, or some variation on that.

Modern tanks have a lot of baffling and air volume when filled and the way the car sits when filling can easily make a 1-2 gallon difference in some cases as to how much you end up putting in.

Just a guess.

 

[Louie's gone fishing]

The fuel gauge is just a rough electronic guess at how much fuel is in the tank. Watch your trip odometer instead and reset it when you fill up. You might be happier with more accurate feedback. By the way did you fill up under a canopy with neon lights?

 

[robl]

Ha, no, no canopy, but I thoguht it is just ODD, as this is not just a one time thing, this is 15 fill ups of EACH station. Every single time, EVERY TIME, the Marathon gas will give me 200 miles on half tank and go from there, yet the other will do about 130-150 ish, however I do always use my mileage and figure it out, and they give the same MPG........So something is with the brands of gases

 

[peking]

This is dumb! It is what it is.





j/k Robl sits in the cube behind me and just want to cr*p on his thread. PLEASE no hate e-mails! haha

 

[badtlc]

Originally Posted By: robl
Ha, no, no canopy, but I thoguht it is just ODD, as this is not just a one time thing, this is 15 fill ups of EACH station. Every single time, EVERY TIME, the Marathon gas will give me 200 miles on half tank and go from there, yet the other will do about 130-150 ish, however I do always use my mileage and figure it out, and they give the same MPG........So something is with the brands of gases


Its justa matter of one topping off the tank more than the other. Probably the difference is due to an incline at the pumps. One pump can get more gas into your tank. If you are getting the same mileage, the actual gas is performing the same.

At my local QT and Phillips 66, the phillps lot is nice and flat. The QT lot is inclined. If i park with my car facing up hill, the pumps usually stop about .8 gallons early.

I still get the same mileage, though.

 

[Dyoel182]

Originally Posted By: badtlc


I still get the same mileage, though.


Thats like getting free miles!

 

[Louie's gone fishing]

Average it out over my fill-ups, like 10.

 

[robl]

I have on 15 tanks each, from 3 separate Holiday Gas Stations and 4 separate Marathon stations around me, 30 total full fill ups, 15 on each, I ALWAYS get to 200 miles (on the needle to half tank) on Marathon, yet the needle ALWAYS shows 130 on half tank on Holiday.

Again 1/4 tank, ALWAYS shows 125 miles on the Marathon, yet Holiday is around 80'ish. But then when I figure it out, the mileage is pretty similar. I just think it's odd brands of gas can make your gauge get to 200 miles on a half tank, then slow down the rest of the way on the gauge, where as the other brand shoots to 120, 130 miles, then the gauge slows down till empty on that other brand.....

 

[Dyoel182]

You're saying that different brands of gasoline make the float float differently?

 

[NYSteve]

Sounds as if the calibration for the pumps differs. They can still be legally "in-spec", but maybe the little bit of difference is why the gauge reads different for the "same" amount of gas.

 

[Louie's gone fishing]

Are you still under that neon lighted canopy? Remember the powder from those lights is not the power you sniff to make the numbers add up correctly.

 

[badtlc]

Originally Posted By: Dyoel182
Originally Posted By: badtlc


I still get the same mileage, though.


Thats like getting free miles!


No it's not. It is like doing the math properly.

 

[Shannow]

some guages work on capacitance rather than level...might make a difference.

 

[glennc]

Capacitance? I had no idea. Can't imagine it. Capacitance through the fuel itself or through a sensor of some kind? How does it work?

 

[Shannow]

Ford Falcons down here in the 80s went to a capacitance fuel gauge.

A couple of metallic strips, held in a particular (profiled) spacing). As the air/fuel interface rose and fell, capacitance changed, and the gauge read the effect...no moving parts.

 

[glennc]

Very interesting. I suppose the capacitance in the air space above the fuel would be high and that in the fuel would be low as the fuel would I presume conduct current between the plates. One weakness compared to using a float would be that some discrete number of plates would need to be used, whereas a float's height can vary infinitely.

 

[Dr_No]

Sulphur deposits can inhibit conduct on the fuel level sender causing the gauge to mis-read.

 

[Jonny Z]

Originally Posted By: peking
This is dumb! It is what it is.





j/k Robl sits in the cube behind me and just want to cr*p on his thread. PLEASE no hate e-mails! haha


Design error. The design engineers were goofing around on the internet, instead of designing a proper fuel gauge.