Prius C tank capacity more than expected...

Gasoline expands and contracts depending on temperature variations. Like, if it's supposed to be hot this week and the gasoline you buy is on a real cold morning, then, as you use the car going into the hot week, the gasoline expands a little more each day, so that as you use it up, it looks like you ended up using more gas than you put in.

 

It's a bad idea to top off the tank. There is a gizmo (don't know the technical term) that prevents fumes escaping, and if you soak that with gasoline it's not good. There is just no reason to top off, and it adds to pollution (the whole reason to drive a Prius is reducing pollution).

 

I always fill my tank to the top of the filler neck. I did the same thing on my 08 Prius and never had a problem after 2 years of use with 60K miles. Everyone has their own opinion about topping of their tank and a lot of them just don't know or understand the system design. It's not a GIZMO. It's called a Vapor Canister. It's filled with activated charcoal.
It captures fuel vapor and sends it back to the intake manifold to be burnt in the engine during a purge cycle. I have never seen a canister failure form topping off the tank, on any motor vehicle. I have seen canisters fill with gas due to other causes, but never topping off.

The reason you are finding a tank capacity discrepancy is, they don't rate it filled to the top of the neck.
It's rated by volume during the design. Most of the time when the pump kicks off, you'll be around that rated capacity.
I always get about 2 extra gallons when I top it off after the pump kicks off. I usually get about 120 to 140 miles before the gauge drops the first tick from full.

Topping off the tank will not cause pollution. It's a sealed system. Please don't spread urban interweb legend as truth

 

WOW! This is quite the most inaccurate assumption I've ever heard.

Yes, gas expands and contracts with temperature fluctuations, but it can't make it look like you had more gas.
The expansion is a Vapor and it won't register on the fuel gauge. As soon as you drive away from the pump, you'll start using the fuel in the tank and you'll have room for expansion. My station is about 5 miles from home. I OVERFILL my tank on purpose, every-time I fill up.

 

I don't know I always fill up long before that. I never let my tank get too low. The fuel pump is cooled by the gas in the tank. Running it very low could allow it to be damaged from excessive heat. Most impellers are plastic.
My wife has abused her Matrix pump a few times by running it low and also ran out 1 time. The car has an extended crank time and I know why. I don't like to run it low. There's just no reason to do it.

 

No it's not. Why do you think people say "fill up on cold mornings"?

But I'm glad your response is colorful, look I can use colors too!

 

Because they believe the urban legend... thanks for proving his point.

Tanks are underground and temperature takes much longer to affect them. It isn't daylight long enough to heat them enough to matter.

 

snopes.com: Tips on Pumping Gas

 

k sry, I thought it expanded a lot more than 1%

 

It's okay! Just funnin with yah.

 

I tried to see how far I can go on one tank. I eventually ran out of gas after 580~ miles, with the computer reading 60 mpg. It's usually off by about 2 mpg so this "looked" like it was telling me I only had 10 gallons. I filled up 1.5 gallons at a gas station I happened to be able to limp to, then drove off. Later that day, I filled the tank, which took about 9 gallons. That makes 10.5 total.

While the tank hold 10.5, I only count 10 gallons for use, because it's difficult to calculate the other half gallon for max range, since the car's mpg calculation is off by different amounts from the real mpg number.

 

Did you fill the tank to the brim before you tried your experiment?

 

You'll need to fill the tank to the top of the filler neck every time to get an accurate MPG and total tank capacity

 

No. I always stop when the pump stops. I assume that anything beyond that is "outside" the capacity of the tank. Not sure manufacturers consider the pipe leading to the tank as part of the tank.

 

They don't, but if you wanted to know how far you can go this information would be useful.

 

The pumps all kick off when the nozzle sensor is tripped, but it's not accurate. Temperature differences, pressure, pump speeds, how far you stick the nozzle in the tank and a host of other variables will cause it to kick off at different times.
The only true way to know is to fill it to the top of the tank, every time. Anything less is totally inaccurate

 

What would constitute the top of the fuel tank?