Anyone get BETTER mileage than the trip computer estimate?

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Originally Posted by Draigflag

But how accurate are the instant MPG readings? I find the slightest adjustment to throttle can result in the figure dropping to stupidly impossibly low figures. In neutral going down hill it reads 99.9 MPG, in gear coasting down hill it reads 0.00 MPG.

That's because your car is using DFCO(decelerating fuel cut off).
While in gear, the ECU shuts off fuel to the cylinders while coasting. While in neutral, some fuel gets burned to keep the engine spinning.

Just because the car DFCOs while in gear doesn't necessarily mean more fuel will be saved from coasting in gear on a trip. While in gear there will be engine braking slowing the car. Great for reducing brake wear when you need to slow down or simply the speed in check. Not so great if you end up burning more fuel than saved in order to reaccelerate after the coast.

That said, instant MPG can fluctuate rapidly and wildly at times. I don't look to it to see what my fuel consumption actually is, but to see if it gone up, down, or stayed steady. That can tell me if a change I've made or in the trip conditions is good or bad, or if I simply lost focus and let my foot get a little heavier on the pedal.