C's Fuel Tank Overfills...Again!

Sounds like you need to change gas stations.
As far as the MPG measurements are concerned....it is a lot easier in a G3, at least for me. I drive until the MDF starts fussing at me, and then I go about 25-50 miles further. Then, I'm usually able to pump 10.0 gallons of fuel. This makes for fairly easy math, and consistent MPG measurements since I always add the same amount of fuel to the tank.
If you're that worried about accurate MPG measurements, you should drive your car until your DTE allows you to pump precisely 9.0 (or 8.5) gallons of fuel into your tank.
Of course, you will deprive yourself of the joys of trying to tamp an extra 0.00234 gallons worth of fuel into your car, and perhaps save your evap containment system from ingesting fluid rather than vapor, not to mention the environmental impact from spillage.
Over the course of several tanks, presuming that you're able to accurately dispense fuel, you'll get pretty much dead-bang accurate MPG readings at the cost of perhaps two or three percent of your tank range.
Many Prius drivers seem to be overly interested in tank range rather than efficiency, which is probably why the G3 starts screaming for fuel when there is still > 1.5 gallons of fuel remaining in the car.
You have to hand it to the folks in Aichi. They know their market.

Fueling should be....swipe, pump, click, done...unless like me, you stop it at a point before the pump shuts itself off.
If the station's pump is not shutting itself off, notify the owner if possible, and change stations. If you're one of those people who tries to stuff extra fuel into your tank....hey. It is your car, but you should be aware that you could be wrecking your ECS, distressing your local environment, etc.
It's highly unlikely that your car could be causing itself to overfill, since IIRC a non-sealed fuel system will throw codes----but you never know. If your car does this repeatedly at several filling stations, it might be time to take it to the dealer and try your luck with Toyota Service.

Good Luck!!

 

I fill until the nozzle shuts off then usually a pump or two more of the handle for good measure. Never overflowed on me. I bet it is the station.

 

I also fill on the first notch/first click but have not overfilled since the old days of the less advanced mechanical pumps.

The only thing I take care to do is lay the nozzle into the tank gently and without encumbrance. Not too far out, not too far in. So far (knock on wood) so good.

 

Try switching pumps (and/or stations), and maybe increasing the flow rate? If the autostop's relying on splash back to trigger it, maybe the low flow rate doesn't give enough splash?

 

Change gas stations. First time is a mistake, second time is habit,