Managing Fill-Ups with the Trip Odometer

[Bluesky 07]

The whole "when to fill up" question seems to come up regularly given that the light comes on pretty early and the range mileage isn't entirely unreliable. Here's what I do, but YMMV - literally in this case. ;-)

I have an '07 Sport and here's the math:

Fuel capacity = 23 gal

My average MPG = ~17 (based on years of recording miles traveled/gallons to fill)

So:
1. Reset trip odo at each fillup

2. True range should be ~391 miles (23 gal x 17 mpg), but reduce each figure to be conservative: use 22 gal x 16 mpg = 352 miles

3. Watch needle & light but use trip odo to determine when to refuel

4. Put in 15 to 18 gallons and think, "I really have to cut my safety margin" but never do it for fear of being "that guy" who runs out of gas in a vehicle with a light and a generous reserve after it comes on.

Do this for a bit and you'll get a great feel for when you need to stop for gas. For example, I was watching MPG in real time via OBD Fusion on one road trip and knew the average was up around 20 on that leg. The trip odo was 405 or so when I ran out of nerve (not gas!) and filled up even though I knew I had at least 450 miles of range. And yep, still had ~3 gal in reserve, though you wouldn't have known it by the way I was sweating driving down I-24 with the light on for 45 minutes and the gauge needle buried below E.

Other times, for instance if I've been offroading, I know the average will be lower so I'm more conservative.

 

[Inv4drZm]

With my truck, when the needle is at E, I have 3 gallons left. On roadtrips, for quick math multiply that by 11mpg and you get a conservative 33 miles to find a fuel stop.

 

[Racso]

I have been keeping track of my mpg and the highest I’ve gotten is 19.66/gallon on a V8. I use the trip odometer and divide that by the gallons I put. I always fill my tank all the way every time I get gas. Once I get bigger tires I just might stop keeping track of the mpg.

 

[riceandpho]

tire size will make the mileage off a little.
im not sure what im getting for mpg, i have 32 inch tires and speedo healer installed, not sure if that is even make my mileage accurate. my drone app and odometer do read a little differently.

 

[JONBOY345]

tire size will make the mileage off a little.
im not sure what im getting for mpg, i have 32 inch tires and speedo healer installed, not sure if that is even make my mileage accurate. my drone app and odometer do read a little differently.

If you have the speedo-healer installed and your speedometer agrees with GPS on flat level land, your mileage on the odo and trip meter is correct as well.

It'll help make the computer milage estimates more accurate, but mine are still off anywhere from 1 - 3 mpg on any given tank.

 

[Whamola]

This Summer was wild...I was getting over 400/tank. Once got to about 450, but was running interstate wide open no stops for 4-5 hours a leg. Sure wish that v8 had any sort of City fuel economy. I'm normally about 315-325 / tank.