My 2020 Prius excellent report!

If you refill till the pump shuts off, call it done, time after time, you'll have a failrly consistant fill. Any vagaries in one tankful will cancel out in the next. Overfilling is bad for a number of reasons: it can and does damage the vapour control components back there, leads to spillage, and so on. But hey...

 

It certainly is ... and also depending on which gas pump, and a few other factors.

Mendel's point about the vagaries canceling is, put another way, that variability is unbiased, and using that same criterion consistently will still give you quite good calculations of your fuel economy over time.

If you drive so much that filling up a gallon earlier would inconvenience you, you're going to find it very inconvenient after persistent topping-off floods the ORVR system and you can't get more than 2 gallons in at a time without it ending up on your shoes.

 

Will do, thanks.

 

If you are talking topping off, I give my gen 3 a good shake at the pump and get another 1/2 gal or so into it.

 

i guess if you've been topping off for 200,000 miles without a problem...

 

The scare stories about "topping off" can come true if you overdo it, but not if not. Toyota's dire warnings on that topic are intended to avoid trouble even in a worst-case scenario (combination of inclined fill-up spot, inclined parking spot, temperature changes, manufacturing variations, etc.).
The 4th generation may be different, but I understand the 3rd will accept at least 2.0 gallons of top-off, without shaking if filled in a reasonably level spot. Therefore, I limit topping off my 3rd-generation to 1.5 gallons (without shaking the car), and have never had a problem. That much only if I don't expect to park the car afterward in warm weather before burning off at least half a gallon. Otherwise, I limit top-off to 1 gallon or less. Again, those specific numbers may not apply to the 4th generation.