There is lot of discussion about why you get better gas mileage in the first half of the tank vs the bottom half. Some say it is the sensor that is the root cause as opposed to some fuel evaporation.

I believe it is the sensor but isn't it a matter of simply calibrating the dial on the gauge for more realistic readings?

 

I think it has to do with the shape of the tank. I have never had a car where it doesn't take longer to go from full to the half way mark vs from half way mark to empty.

 

It is typical of most cars for the gauge to go to empty quicker in the second half of the tank. There's no calibration (I'm aware of) or a sensor to replace. There are actually 2 sensors in the tank and, on top of that, the ECU estimates fuel usage based on injector cycles.

In other words, the gauge is not accurate. There is no evaporation of the fuel or increased consumption.

 

Those analog gauges are NOT to be trusted.
Look into your "RANGE". and don't let it go below 30miles remaining.

as for me, i never go below the halfway mark on the needle.
it's easier that way

 

The automakers calibrate the fuel gauge to go slow in first half on purpose. Psychologically a happy feeling for the driver.

 

The RANGE indicator cannot be trusted. Or maybe it is just my 1.5 month old 2013 RX350 having a defective measurement unit.

Ran fuel tank down so the fuel consumption screen showed 7 miles cruising range in the NAV screen. The screen above the steering column stops showing cruising range when it drops below 14 miles. At this point, I put in about 2 gallons at a very expensive gas station intending to fill up later at a reasonably priced gas station.

Now the cruising range showed zero miles. Yes, less than what it was when I pulled in for the fill up. It should have added about 36 miles considering 18mpg advertised mileage. Definitely should not have been zero. Even after an ignition stop and start after several hours, the range did not show correctly. This has happened to me twice. After a subseuent full tank fill-up, the range indicator starts behaving as before.

 

At what time did the yellow fuel empty light came on?
That's why i don't let the range go below 30 miles, which also means you have the warning for Empty on the fuel gauge ON already.

The problem with your situation, is you only put 2 gallons.
It probably replenished the "reserved" only.

I have owned/still own non toyota/lexus cars and my experience is that the fuel gauge is not divided proportionately. This is also the reason why you can go above the Full and below the Empty and still drive the car for another 50-70 miles.

 

Only 2 gallons of gas did not reset the fuel counter, as not enough difference was detected in the gas tank level sensors. The ECU continued to estimate remaining gas based on injector cycles. It is normal. Try putting a couple gallons more gas in the tank next time. I know 5 definitely triggers the gauge to reset.

 

I haven't noticed much on my Rx 350 but I will definitely keep that on look out.