Does it matter whether you fill your tank after it's near empty or when it's only 1/2 empty?

I can't say if there's a significant difference, but fuel adds weight. The more your vehicle weighs, the more fuel it burns to haul it around.

Less weight = better FE.

 

voc are released when you fill, so decreasing the numbrer of times you fill the tank slightly decreases pollution. Over filling the tank releases more damage, so topping is bad.

 

If you are going to fill twice as often, wait until empty, then fill 1/2 way.

 

I don't really like going to the gas station so I've tried to do this as little as possible, always waiting for 100 miles or so from when that last fuel bar starts flashing. Even so, there are still times where I only put in 9.5 or 10 gallons, meaning I could have gone another 100 miles before the fill up.

 

lol. That's a different issue, family. Go ahead and just don't over fill it. You really are causing very little extra pollution to solve this family politics. Let them pay every once in awhile

 

The tank is half full, not half empty.

 

My filling schedule is very dependent on hurricane season and status. VERY dependent.

 

In your case, I guess the answer is yes - but only for the HOME environment! If it were me, I'd think "free gas!" whoo hoo!!

 

burritos, I understand the situation as i was there when my Grandparents were alive. They aren't going to change & you can't win. Let go of your emotions & enjoy their kindness. Let them know it is appreciated. Maybe you can come to an agreement on a schedule--you fill this Tuesday, I fill next Tuesday.

When I carpooled the agreement was "this week I drive, next week you drive". Miles didn't matter. Days didn't matter. Gallons didn't matter. Fuel economy didn't matter. It worked as long as the timing did. A schedule change ended the carpooling to our mutual regret.

 

As AG has said, in big industry storage tanks as well as car fuel tanks, the biggest source of pollution is when you fill the tank, the VOC vapors are pushed out (unless there are vapor recovery controls).

Prius is an ultra-clean car so there is vapor recovery and the Gen-II had the bladder flexible gas tank to prevent the vapor releases on fill-up. So for Prius it does not really matter if you fill whole tank or half tank.

Lets instead take the case of a car with no vapor controls. Probably does not matter too much in that case either, but there might be an argument that filling half tanks puts more vapors in the air than waiting for the tank to be empty.

 

This isn't about environment, even though its a bladder gas tank, calculated mpg is normally the same 5-8% off over MFD but I seem to get better MPG filling up around half -two pips below half of a tank of fuel left. The 2 times I have filled it up on the last pip, I am looking at a 39-41mpg cal. vs the average of 44-46mpg when I fill up sooner.
Just my 2cents worth..