I was reading on a 2nd gen Facebook group about how you "can't go by the MPG readout on the dash and have to track miles and how much gas it used". The 2nd gen gas tank uses a rubber bladder, and I was under the impression you can't calculate gas usage the "old school" way because if it's say 67 degrees when you filled up last, and 87 degrees when you fill up again, the amount of gas the rubber bladder can hold will change.
The bladder tank can definitely skew the calculation of a single tank, but over multiple tanks the variations will inherently cancel out. Calculated is still your best bet. In my 3rd gen experience, the mpg displayed in-dash is ~7% “optimistic”. Gen 2 I’d suspect is similar. AFAIK Gen 4 continued this tradition. For Gen 5, just from what I’ve read here, Toyota finally is keeping it honest.
I disclaim that my experience comes from gen 3 and gen 5, but I have found that there is probably intentional inaccuracy in the gen 3. The computer system is capable of high accuracy in speed measurement for the purposes of operating the hybrid system. But regulations allow a 5% tolerance on the speedometer/odometer, and Toyota uses this to its advantage. This yields slightly better fuel economy, and it shortens the warranty coverage period (by 5%). I was able to verify this by timing my speed on a test track. The speedometer reads 5% higher than actual speed. I have not observed this in my gen 5.
Don't conflate speedometer variance with the odometer accuracy. Regulations do not allow "5% allowance in the odometer", and if Toyota was doing that, they'd be in court in a heartbeat. Honda got spanked for just that, a few years back: https://www.cbc.ca/news/honda-canada-settles-class-action-suit-over-odometers-1.860237
The bladder don't have much to do with mpg me thinks. Once you start filling and driving a gen2 regularly you'll stretch that bladder in 5 months. I went from filling 15 min at pump to a 2.5 min fill up in this time this is unassisted filling me setting lever and watching went from placing lever cutting off at 2.8 gallons or such . To wet 8 can drop 8.4 in 3.5 min or less standing they're . I do it several times a week at Sheetz only blue fuel
What's extra funny is that the exaggeration of the speed is clearly just built right into the speedometer. If you use an OBD scan tool and view the vehicle speed PID reported by the skid ECU (which is the value the speedometer relies on), it's accurate. And the speedometer display is digital, not any kind of approximate analog movement. So it's pretty clear there's some line of code in the combination meter that takes the accurate value from the skid ECU and multiplies it by 1.05 or something to exaggerate it for display. I'm not sure that's necessarily the same value used in MPG computation though. Inaccuracy in the MPG computation may have other sources.
I was able to verify at the time, that auto manufacturers were allowed a 5% tolerance on the accuracy of speedometers and odometers. As I said, I don't know if it's true any longer.
