Ok, so i just got back from the pump and something strange happened. This was my 9th fill up and throughout all of my fill ups it would usually fill about 14.5 - 15.0 gals when the range indicator reached 0. And i always fill to full. However, on this last fill up again with the range indicator at 0 it filled only 13.2 gals. I thought this was abnormal.

On top of that my "After Refueling" average showed only 35.1 mpg for the tank, however if i divide my miles driven (which was 511) by 13.2 gals it would mean that i really did 38.7 mpg. I also thought this was peculiar due to the fact that the best mpg that ive done so far since i bought the car has been 35.2 and my all time average is 33.8 mpg so im not sure if i really did 38.7 mpg or not now, im really confused.

What i know for certain is that i did really fill 13.2 gals because i checked my statement and the prices matches with the gallons. So either the "After Refueling" indicator was off by 3.6 gals the other direction, which is very strange or my fuel gauge is not working properly.

What are you guys input on this ?

 

Maybe the pump stopped early? There could have been an air lock in the tank and the pump cut off earlier than usual. I've never gone down to 0 range, I usually fill up with 60-100 km remaining range and I go by money amounts, not by volume. Easier for the attendant to punch in on the pump console.

 

Thats what i thought as well but it i tried the pump and it clicked again also my fuel gauge is all the way full and my cruising range also indicates full range, im sure its full, cant explain it

 

I have only run my ES fuel tank down that low once and it took 14.0 gallons to refill, so thats about the same as your refill amounts. Generally I try to avoid running it that low.

Was your last fill up at the same station and pump as previous fill ups? Different pumps can shut off at different "full" levels. Also the slope of the station driveway can effect the shut off point. If your next fill up results in a lower than expected mpg, then most likely you just got an early shut off on this tank for some combination of reasons.

 

I think delivery rate (fastest) of gas can also shutoff the pump sooner. You may have another 1/2 gallon before it's actually full, which is closer to your previously fill ups. It's hard to consistently ensure you're getting to the same level. Regarding the displayed mpg, I don't relie on it but calculate the trip miles by the gallons used as you've done on this fill.

Congrats on getting getting up to 38 mpg.

 

Every pump nozzle is different. You need to stick to same gas station and same nozzle if you are going to do an experiment to reduce variations.

 

I'll second that. IF you want to do such an experiment, it is important to eliminate unnecessary variances.

But, of course, after the "new" wears off, it really is just a car. The difference between X and X+0.1 miles per gallon really doesn't matter. This is particularly true if you spend (time/money/fuel/worry) on getting the experiment exactly right.

 

I cannot recall the exact number of gallons my last fillup required, but miles travelled were nearly identical to those you indicated in your post and my calculated MPG was 38.2. The dash actually read 40.2 MPG. This difference between dash and calculated is consistent with our RX and former Toyota so there is clearly some margin of error.

I realize this is just the opposite of your situation, where the dash read lower than calculated mileage, but I have had that happen before too. I calculate every tank by hand, and if the RX shows lower than calculated, it is never more than a partial mpg low. Conversely, it usually reads about 2 mpg higher than calculated - which has been our ES experience so far.

I assume the dash estimate is based on many factors that vary as the tank drains. I wouldn't be surprised if altitude, temperatures and even humidity could be used in the running estimate. I can't offer anything more than my own observations but I wouldn't be worried. The Prius supposedly had a bladder inside the tank, and it wouldn't always take a full tank in extremely cold weather. I wonder if that tank configuration is used by all Toyota/Lexus hybrids and could account for slight variations in fill levels?

 

thats very interesting, it has been raining here for the past 2 days and it is very cold relative to our normal temperature, maybe that could be it. I guess ill know for sure when i refuel the next time.