Mpg Suddenly Improved For No Reason?

[FoolishFil]

I'm a first time poster - so bear with me if this is the wrong place to post.

I only joined because I can't think of an explanation - any ideas?

I've got a 2.2 D4D T-spirit Avensis, on a 57 plate.

I've always got about 45-and-a-bit MPG out of it - i brought it at about 65K miles, and until about 78K miles, it was really consistent (based on the MPG readout, at least) - i.e. not 44 MPG unless i did lots of town driving: 45 MPG, month in, month out.

Then suddenly - over a day or so - the average MPG shot up to 50 and a bit MPG.

My commute - 40 miles a day, mostly motorway - hasn't changed

My driving style (sedate, unrevvy) hasn't changed.

About 600 miles before the sudden improvement, I had the water pump changed.

About 150 miles before the improvement, the front right wheel had a sudden screeching/grinding, and - after some worry - a local garage extracted a small stone (though without tellilng me where from, annoyingly in hindsight) and it's been fine since then.

Was last serviced about 2000 miles ago - a few consumables, nothing exciting.

I can only think of three explanations:

1. The MPG has suddenly gone sightly wrong. (but this feels so unlikely - electronic stuff works or it doesn't - it doesn't go wrong by 10%)

2. The stone was actually grinding away for 10000 miles slowing me down, but shifted and something freed up (but the stone didn't look ground down at all)

3. Something - not sure what - cleared in the engine (but what would cause such a big improvement?)

What could have caused this? I'm happy about it, it just's bugging me not having a theory that sounds sensible.

Thanks in advance

Phil

[Cyker]

How long have you had it?

Without any more info, I would say the most likely explanation is the weather - Diesels are incredibly sensitive to temperature as they love to run hot for maximum efficiency.

(Which is why things like EGRs on diesels are so stupid! )

[Parts-King]

I would do a manual calculation based on fuel used over mileage, it could be that it's something as simple as an error with the display calculation

Kingo

[FoolishFil]

Cyker - I've had it for about two years now, done about 15,000 miles in that time, with most of that in the past year or so. The 45 MPG was rain and shine, summer and winter.

Parts-King: you could be right - though it seems odd to have such an error. I think you're probably right to double-check against reality - but if I can't trust the MPG, can i trust the odometer?