In my experience any recent trip computer is more accurate than doing calculations with the amount of gas pumped on a single tank. The problem is the mechanical gizmo in the gas pump that shuts it off when the tank is full just isn't that reliable. If it cuts off a gallon short it'll look like you got better mileage than you actually did, then the next tank looks bad since the next pump actually filled your tank, or maybe even overfilled it a little. There have been plenty of times when I've caught a pump cutting off way too early. I know about how much gas I need if I have a half or quarter tank left and if it's a few gallons short of where it should be I know it was an early cut-off, but if it cuts off a gallon short I won't notice. I figure that has to happen at least as often as a way too early cut-off. I've also been overfilled a few times, the worst one being a pump that just didn't cut off until gas was running out of the tank and down the side of the car. So best to not think too much about a single tank and just keep a running average. A gallon or two either way won't make much difference over 10+ tankfuls, but can really mess with your numbers on a single tank.
That's why I have a routine I follow when I fill up. Let it go until it shuts off, wait a couple of seconds for things to settle down, squeeze until shut off again.
That first shut off is the unpredictable one, with the gas swirling around in the tank and sometimes forced up the filler neck.
I have been following your recommendation on my fillups since your last post here PF. My Fusion now has about 5700 or 5800 miles on it. I have been running between 41 and 43 mpg and I am totally satisfied with those numbers. I always used to fill my cars that way until I saw on TV or read in the Local paper's auto section that it is best to stop fueling your tank on the first automatic shut off. I guess the reasoning was that way you don't accidentally over fill it. Anyway it made sense to me to go back to my old way for better accuracy. I am finding the longer I have the vehicle the less concerned I have become about worrying about every fill up. I still have been recording things just to watch if there is any sudden spike up or down in Mpg.
2012 Highlander Limited AWD V6 and 2015 Ford Fusion Hybrid SE
I have been following your recommendation on my fillups since your last post here PF. My Fusion now has about 5700 or 5800 miles on it. I have been running between 41 and 43 mpg and I am totally satisfied with those numbers. I always used to fill my cars that way until I saw on TV or read in the Local paper's auto section that it is best to stop fueling your tank on the first automatic shut off. I guess the reasoning was that way you don't accidentally over fill it. Anyway it made sense to me to go back to my old way for better accuracy. I am finding the longer I have the vehicle the less concerned I have become about worrying about every fill up. I still have been recording things just to watch if there is any sudden spike up or down in Mpg.
That's EXACTLY what I use my mileage calculations for... determining the general health of my car. Not so much on any single tank, after all, it's possible to have a "mis-fill" that can throw the mileage number out of whack. For example, if I've been averaging 32 mpg and suddenly I get a tank that figures out to something like 28 mpg and nothing in how I'd been driving recently could account for it, that gets my attention. I make sure my fillup is normal, then wait until the calculation at the next fillup. If the numbers are back to normal, great. If it's still down, something MUST be going on. A simple way to monitor thing in general
I always used to fill my cars that way until I saw on TV or read in the Local paper's auto section that it is best to stop fueling your tank on the first automatic shut off. I guess the reasoning was that way you don't accidentally over fill it.
Overfilling can mess up the vapor recovery system too. But it's hard to break that habit of topping up.
I got a "new" used car a year ago and intentionally stopped keeping a gas log. It does have the dash readout and it's been pretty accurate when I've checked it manually. I sort of miss the gas log ritual.
I'm not topping off as much as letting the gas "settle". It's like when I fill up my yard tractor from the gas can. If I go slow and pay attention, I can let the gas rise in the tank until I see it about to come up to the filler neck. If I'm pouring too fast, the gas is sloshing around and sort of trapping air in the tank. Even if the tank doesn't overflow, once the trapped air makes its way out the top of the tank and I have a short fill.
With the car, I let the pump shut off by itself, can hear the gurgle as things settle, then squeeze until a second and third shutoff. No overflow messes for me
I always used to fill my cars that way until I saw on TV or read in the Local paper's auto section that it is best to stop fueling your tank on the first automatic shut off. I guess the reasoning was that way you don't accidentally over fill it.
Overfilling can mess up the vapor recovery system too. But it's hard to break that habit of topping up.
I got a "new" used car a year ago and intentionally stopped keeping a gas log. It does have the dash readout and it's been pretty accurate when I've checked it manually. I sort of miss the gas log ritual.
Thanks to both you and PF for your thoughts on this. I think I will give my Ford Dealership a call for their suggestion about fill ups. I have been very sensitive about this car's fuel efficiency because I have never owned a Hybrid before and never ever thought I would. Also, I have actually over 6000 miles on the car now. Pretty much broken in so hopefully the Mpg will remain fairly steady.
2012 Highlander Limited AWD V6 and 2015 Ford Fusion Hybrid SE
I spoke with a Mechanic that has serviced our cars for the last 10 years about this issue today. He strongly suggested that I stop at the first click. Said it could cause the issue stated above and was not worth the extra probably 1/4 extra gallon to get a more accurate mileage calculation. I will just rely on my Car's Computer for my results and assume my actual is probably within 2 mpg.
2012 Highlander Limited AWD V6 and 2015 Ford Fusion Hybrid SE
Comments
That first shut off is the unpredictable one, with the gas swirling around in the tank and sometimes forced up the filler neck.
For example, if I've been averaging 32 mpg and suddenly I get a tank that figures out to something like 28 mpg and nothing in how I'd been driving recently could account for it, that gets my attention. I make sure my fillup is normal, then wait until the calculation at the next fillup. If the numbers are back to normal, great. If it's still down, something MUST be going on. A simple way to monitor thing in general
I got a "new" used car a year ago and intentionally stopped keeping a gas log. It does have the dash readout and it's been pretty accurate when I've checked it manually. I sort of miss the gas log ritual.
With the car, I let the pump shut off by itself, can hear the gurgle as things settle, then squeeze until a second and third shutoff. No overflow messes for me