Our TCH came with a "full" tank of gas but wasn't apparently completely topped off because the next fiil up I topped it off and then the mileage increased about 4 tp 5 MPG.

 

How much different between the computer mileage and real mileage? I still have to wait about a month to go. Would someone tell me your experience?

After 12,500 miles my actual calculated FE is 0.9 mpg lower than the computer indicated. It does vary from tank to tank though, sometimes by as much as 3 mpg. I'm convinced that a lot of driving in the E mode or at the 60mpg mark goes beyond the accuracy of the fuel measurement calculation (accurate fuel flows are difficult to measure accurately in the range from E (no fuel) to 60FE (idle while cruising at 70) to full 15 mgh readings (while accelerating onto the interstate).


(there are detailed threads on this here and on Edmunds)

Here is a comment I just took from an edumnds posting. I had mentioned the speedo error and the odometer error. Once again in a state of confusion I have been corrected and I'm glad. It explains a large "chunk" of the indicated FE error

<i>but I believe that our FE calcs would be lower (too low) than actual, not higher...</i>

I will admit to allowing this to confuse me a lot but I believe you are right.
Interesting too because if I drive 500 miles (by the odometer) then I actually have driven 507.5 miles. With a 13 gallon fill up instead of 38.46 mpg I would have 39.04 mpg. My computer FE reading is averaging 0.9 mpg higher than my calculated average (using the odomoter reading. This would account for 0.57 mpg of that error and make the computer reading closer to actual calculated. Perhaps Toyota did indeed include some "correction" into their formula?

This would make my indicated FE within 0.3 mpg of my actual calculation. That's a reasonable error.