Has anyone noticed a step change in economy after their cars have gone certain distance? Mine's done about 22,000km now.

Reason I ask is because last Sunday, I did a round trip from Sunbury to Bendigo in the morning, then from Sunbury to Altona in the afternoon. Normally the consumption going from Sunbury to Altona (by the MFD #1 display) is about 5.5/100km, and the return about 6.1l/100km. On Sunday afternoon it showed 4.9l/100km for the southbound trip, and 5.9 for the return, and I've noticed that the instantaneous reading has improved as well - sections where it would normally be 4.5-5.0 are now 4.0-4.5, regularly staying under 10 even on decent hills, etc.

The only thing I could think of was lower mass in the car as the tank emptied, but then I've had quite a few variations of load (ranging from single person and empty tank to 4 adults, luggage, 3 dogs, AC, hot day, full tank) over the same trip and never had as great a variation, plus I refuelled last night and it still showed 5.9 for the return trip.

And while the MFD is optimistic, it's still backed up by the distance per tank and the true economy - the prior 3 or 4 tanks have been around 6.4l/100km with about a 60/40 country/town split and about 940-960km/tank, last night's fill was 6.17l/100km with about 65/35 country/town and 1008km from the tank (MFD said 6.0 exactly).

The only times I've had better than that have been for long flat country driving, Melbourne-Newcastle, Melbourne-Shepparton, that sort of thing, getting around 5.7l/100km for a tank.

I'm not complaining, just wondering what's happened to suddenly improve the consumption.