Better mileage when tank in full vs less than full?

So why does the 16 Tacoma show better mileage 27.8-28.3 when the tank is full and around 25-26 when 1/4 to 1/2 full, same driving conditions, same stretch of road??

 

Because the dash readout isn't accurate. The only way to calculate your mileage is with math applied across an entire tank. Or at least between fill ups.

 

Assuming you have the 2.7? I would think it's due to how you drive it right after filling up vs the cumulative driving effect when you get to 1/4 - 1/2 tank. My readout is pretty accurate, no more than .1 to .2 off and many times spot on.

 

That display is a random number generator.

Mine shows 14-19 MPG, yet I know I’m getting better than that.

 

I find that to be the case too, when I fill up and hand calculate it matches the display within .1 or .2

 

Bully to those saying the readout isn't accurate. Mine is dead on. Don't bother with hand calculating anymore.

 

The higher my tank average display shows (road trips) the farther it it gets from hand calc mileage. If display is showing 22mpg tank average it’s usually at least .5mpg off from actual (21.5mpg). It’s been .6-.7mpg off before. Most of the time it’s a consistent .3mpg off though. I don’t trust my truck read out at all lol always displays better than actual.

 

Will it choose my lottery numbers?

 

When its near full its averaging only a few miles. When its near a 1/4 tank its averaging 300 miles plus. Mine does the same thing.

 

Exactly this. The more data compared the higher the accuracy.

 

Don’t believe what your dash says, it has only to do with speed (acceleration and deceleration), weight and drag (friction). Less of any of these increases your MPG.

 

Just filled up now. 402.7 miles. Same gas station I use 19 times out of 20. Trip display showed 23.5mpg (was 23.6mpg while waiting in line for gas). Put in 17.844 gallons. Hand calc 22.6mpg

If I do mainly all city driving then the trip display usually isn’t off a ton. About .2 or .3 for me. But the more highway miles I do the farther and farther the computer gets off. Almost a full mpg this time. Really makes me wonder about the people who claim low/mid 20’s tank average, but only go off display. Display is not that accurate the more highway I do.

Figured I’d share so others are aware!

 

As fuel tanks empty and fill with more air, this air causes more evaporation and condensation. I know from my pilot knowledge, one of the number one rules of airplane storage is don't ever put the aircraft away on empty tanks. Obviously a little water or lost fuel isn't going to hurt us as bad on the road.

I have noticed in every car I've owned the fuel mileage is worse the closer I get to Empty. I'm not sure how the OBDII measures and spits out data but if it's taking fuel still available into account then that would explain evaporation anyway, the more empty the tank.

 

I use hand calcs and never average above 19.5 on a stock truck. Though I live in hill country and I’m convinced this truck sucks at going up hills as far as mpg is concerned.

 

The several times I have checked the dash readout with math, the dash readout was .2-.3 mpg low.

Or within about 1%. Pretty close IMO.

I have not noted what OP has.