My first post to commemorate my first drive we just bought our used 2005 with just under 58K on it for 16600. we filled up the tank just before hopping onto the free way and drove 99 miles home. when we got off the freeway i filled up my gas. the computer on the car said we averaged 55.3 mpg but when i did the math with what i filled up, it calculated to 61 mpg. either way im very happy. and it could just be that the two different gas stations have different "full's". if you know what i mean.
:welcome: Welcome to PriusChat, Elreq! Congratulations on the car! The Prius, at least in North America, has a rubber bladder inside the metal gas tank, as sdtundra suggests, so no two fulls are ever the same. Calculated milage is only accurate over a few tanks and hundreds of miles. In any event, great milage and I'm sure a lot better than you were getting before. There's a ton if information here on PC. Welcome again and happy driving!
Welcome!!! As for MPG you will get a better idea after a few tank of gas. Keep track by hand and the MFD.
It has to do with emissions. Take a look at 2004 Toyota Prius FAQ The information is the same for the 2005. You could think of it like a balloon inside an old fashioned milk bottle, but the balloon can be stiff and not "inflate" the same way each time. Another idea is to take a gallon bucket (with a mark at the gallon level) and put a brick in it. Fill the bucket to the level with water. Did you actually put in a gallon? Nope, but the level (which is what happens at the gas station) says it is. Sometimes that "brick" will increase in size and other times it decreases.