I've noticed that the first 1/4 of the gas tank gose realy fast compared to the rest and always wondered why. Well know I know. Like the tac,temp,speedo,and oil pressure gauge the gas gauge is **** too. I filed up the other day till the pump stoped full right? The gas gauge said it was but my ultra gauge said it was only 94% of my 15gallon tank. At first I thought ok the ultra gauge if off but watched as the OEM gauge dropped and at 3/4 the ultra gauge said 75% watched some more and at 1/2 tank the ultra gauge said 50% so in convolution the OEM fuel gauge if off by 6% at full but starts to read right some where between 3/4 and full. Mazda really put some crap gauges on this thing.

 

Well the fuel gauge doesn't have the same type of potential accuracy as the other gauges. It's a reading of voltage based on a resistive sensor, modified to not show rapid fluctuations. Sure it's not accurate, but it also can't be as accurate so that it doesn't go crazy with fuel sloshing on acceleration or cornering.

Believe it or not, the OBD reported fuel level is actually reading a different sender than the OBD reported one. There is a main fuel level sensor and an additional secondary sensor in the fuel tank. The main one goes directly to the ECU for high accuracy level reporting via OBD, and the secondary goes through a signal cleanup and scaling circuit then to the gauge cluster.

Yes, it's a removal of accuracy to reduce user panic, but it's hardly comparable to what they did to the oil pressure and coolant temp gauges. Without the fuel one, you would be completely unable to know how much fuel you had remaining.

 

 

The fuel gauge in my 8 doesn't behave much differently than the gauge in any other car I've ever owned. There's a traditional behavior. I suspect that if any auto maker ever provided an accurate linearly calibrated gauge the owners of those cars would wind up in trouble, or at least confused.

FWIW, I always reset the trip meter when I fill up. I've got a good idea of how many miles I can go on a tank, under different driving conditions, so I have a backup to keep me from running out. Been doing that ever since I barely coasted a rental car into a gas station in the middle of nowhere some time back.

Ken

 

The gauge on my S2 goes super fast the first quarter then become normal. Honestly, who cares since gas stations are everywhere. Might as well just give us an indicator. Motorcycles have been the same way since it was invented.

 

It was just an observation that I had made. I have had some conversation with others about the first 1/4 of the tank going so fast and none of us could ascertain as to why till now. I was just shareing what I have found. With this new data I also learned that all my MPG calculations are incorrect as the tank was not truly full.

 

Mileage is the only accurate way to verify fuel mileage.

 

If you fill the tank to the same level everytime which I suspect is probably true then the mpg calculations are close enough for government work. If you only fill it 95% EVERYTIME then it is effectively 100% full despite having remaining volume.

 

Where did you get this info? Have you ever actually looked at the sensors or the way that they work?

 

I always figured the top of the tank probably rounds in and is physically smaller so it drains faster. But i could care less as to why I fill up by 1/4 and the low fuel light has reminded me the few times I haven't payed attention on a long trip

 

The tank has 2 sensors because it is basically 2 tanks that are joined over a "saddle" in the middle.....so with fuel slosh and differing returns through the siphon you can have vastly different readings from each sensor depending on which tank has the fuel

I have never seen a totally linear fuel gauge. Even the gauges on my fuel cell are cranky and not accurate

 

On average, mine is;
F to 3/4 - 60 miles
3/4 to 1/2 - 60 miles
1/2 to 1/4 - 80 miles
1/4 to low fuel light - 40 miles


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Yeah I feel like the fuel gauge is pretty inaccurate. I fill after an average of 197 miles on a tank, and fill an average of 11.8 gallons (yes, I have all my fills in a table in Excel), generally when the fuel gauge is at or slightly under 1/4. Though, after a fill from the pump, my gauge is usually about one notch over full, though I don't top off; just where the pump stops.

It's definitely not totally accurate but it is accurate enough to let you know when fuel levels are getting low.

 

If it was totally accurate you would run the tank dry, overheat the pump, and panic at randomly fluctuating fuel levels.

The fuel gauge is the most accurate thing on that dashboard.

 

More so than speedometer? or odometer?

 

IMO yes, or at least on par with them. They're all offset for reasonable reasons.

 

Fuel gauge is spot on from 7/8 of a tank till just under the 1/2 mark then seems to hange up again at 7/16 of a tank but becomes spot on again around 3/8 haven't run it under 1/4 so not sure about after that.

 

Because of the way the float works, fuel expansion, slosh, etc, the gauge will never be 100% accurate. As much as everyone thinks that they'd like to have a gas gauge that's exact, they would cause more issues than they would solve.