129 miles on a quarter tank?
 

So I think either my gauge is messed up or my car just became a prius. So I drove about 70-72 for an hour on the interstate, shut the car off for an hour and drove back the same way at the same speed, actually about 68-70. So I had a two hour round trip and my gauge read that I only used a quarter tank?? I had fuel injector cleaner the tank, but I don't think that had anything to do with it. I plan on filling up later and seeing how much gas it will need to fill it up, I was thinking of around 11.25 gallons or so, it is right at the 1/4 mark. Any suggestions on checking the sensor without pulling out my fuel pump assembly? or does my estimate of gallons sound right? Help!!
Thanks.

You can gas up and see how much you put it. If the gauge is lying, it will be more than whatever a quarter tank is gallons. But yeah, that sounds crazy :)

Yeah, I think your gauge is askew. I started to have that problem last year and still today. Once I hit 180-200 miles, my gauge needle is stuck on the third tally mark before "E". I have not seen the warning light for low fuel turn ON for so many months and I've run my tank empty four times since last year because of this. I know it is an easy fix but I'm just waiting(another excuse for being lazy) until I can replace my factory fuel pump to clean up gunk out of the gauge sensor/reader since they're in the same area anyway.

So I went to fill up, the gauge was a notch under the quarter tank mark, I put 12.01 gals in... And I read that a guy fit 14.8 gals in his car one time so I am guessing we have a 15 gal tank? so that puts my gauge about accurate I believe? Sooo, my rx8 is now a prius? lol

Unless you are driving in a flat desert the conditions one way vs the other could be considerably different.

Series 1 (2004-2008) RX8s have a 15.9 gal fuel tank. The Series 2 RX8s (2009-12) have one additional gallon capacity in the fuel tank.

http://www.edmunds.com/mazda/rx-8/20...res-specs.html

Fuel quality could play a part in this. I live in MS and the fuel quality is crap so much ethanol you can smell it and my 8 gets about 18mpg on it. Having said that I took a trip to TENN where I emptied the tank and filled in TENN where for the first time in years I could smell real gas not the ethanol. I then got 26mpg out of her till I returned home and had to fill her full of the crap gas here and she is back to her 18mpg. I confermed this when I filled up by how much went in the tank. So heavy ethanol gas gets realy crap mpg in the 8 VS gas with little or no ethanol. I've seen this same thing in my piston engines too not as dramatic but still a bit better.