My 2017 Prius has a gas tank with an 11.3 gallon capacity, according to Toyota specs. Multiple times over the years I have waited until I have zero bars on the fuel indicator. I want to learn the single-tank range of my Prius and compare the impact of the weather/temperature. When I fill up I always get about 9.5 gallons. I have never filled up and reached 10 gallons on the gas pump display. Does Toyota purposely set the fuel tank gauge to display empty when there are actually more than 1.5 gallons remaining? That means you can drive about 75 miles after Prius is “empty.” Is it a safety precaution and/or a law?
Yes, I think Toyota does leave about a 2-gallon buffer on their tanks. But be careful letting your tank get low, especially in the winter. Water rises to the top when it's in gasoline. So if you use up the gasoline any water will then be inside the small gas line and what does water do when it's cold? It freezes and then your car is not going anywhere. This happened to me here in Colorado a while ago when we were having a bellow-zero spell. Now, I never EVER let the tank get below 1/4 in the winter.
Don't think it's law, but is a safety precaution. Most manufacturers have the low fuel light come on when there is a gallon or so in the tank. So E is never fully empty. Then variations in the pump shut off switch, sloshing of the fuel while going in, and angle of the car when filling could lead to getting a short fill at times. Plus the listed volume counts the low point where the pump sits, and that only gets drained when fuel emptied until stalling. With E10 you don't need to worry about freezing fuel. Ethanol is an antifreeze, and keeps any water mixed with the gasoline. As long as excess water doesn't get into the tank. Note water is heavier than gasoline, but the fuel pump draws from the bottom of the tank.
E10 tends to turn to Varnish faster than alcohol-free fuel. Also (& biggest concern we have is) where a partly empty tank allows for condensation to form. Then you have another issue to deal with.
After I posted I realized that I probably should have chosen another category. If possible, please move the discussion.
I'd give $100 to 1 odds the request will be much much faster than a request from the Prius chat store .
SAY WHAT?!?!?!? Hate to break it to you, Boo, but water is heavier than gasoline and sinks to the bottom, it does NOT float on the gas, regardless of temperature. I spent 8 years in the petroleum industry, tested fuel repeatedly for water. We always put the water test paste at the bottom. And on tanks with a sight glass (clear tube used to check level) the water is visibly different in color and always at the bottom. Makes it easy to drain, at least. The main reason to keep a tank full(er) in the winter is to keep out the humid air which will then allow the moisture to condense out of it when the temperature drops and allow it to accumulate in the tank over time. If it happens long/often enough, it will build up until the fuel pump starts picking it up. Then things get bad.
I've seen docs that say you can only fill a fuel tank to 85% of its AIR capacity to allow the fuel to expand now that it is out of the cold underground tank. That is a federal requirement. As far as filling the thing, I've never gotten more than 9.5 gallons (US) into it, either. That time I had 25 miles of range showing, about 1/2 gallon left. My manual said the capacity is 11 gallons. I think it's just 10.
Then with most filling with E10, the water only becomes an issue when there is an inordinary amount of it.
Automotive fuel systems for the past two decades or more, has been pretty much closed loop systems. Any significant contaminates making it into your fuel tank was most likely pumped-in at a gas station. Water contamination isn't going to be an issue as your moving down the road; it's being thoroughly mixed-in as your bouncing down the road. Morning startup is another story, as your fuel settles out and separates. YMMV... FWIW: I've been able to pump 10-10.25 gallons into my tank, a few times - but I've been running zero bars for a while. You need to know your car and conditions your driving in, since the mpg varies widely based on environmental operating conditions.
Something relevant I forgot: Gas stations have filters on their supply lines. For dirt, water and other contaminants since those honking big underground tanks are impossible to get to once buried. The odds of you getting any water into your tank directly from a gas station is negligible, especially if they follow the rules on filter replacements/maintenance. Now if the owner is a cheap, lazy bastard...... The only realistic way to get water in the tank is through accumulation of condensation. For what it's worth: I don't really think it's all that temperature dependent, tho. The air needs to be very humid - like in Florida for example - then when the temp drops at night, the relative humidity rises to 100%, it condenses and accumulates. But in the 35 years I lived there, I never heard of a single proven example of water in the tank. (The E10 may help disperse it, I don't know.) Every time I heard of a "gas" problem it was always something other than the gas: bad pump, line issues, etc. My $0.02
