Sudden decrease in fuel consumption

Back in March 2015 I asked you:
"I bought a 2012 Honda Civic 1.8 EX i-VTEC in February, swapping it for my 2006 2.2i-CTDi. The overwhelming 'feature' of the new car is its enormous thirst for petrol and I am wondering whether there could be a problem as the engine feels stifled below about 4000rpm."

Over the last month fuel consumption has shot DOWN. I'm now getting under 40mpg and don't know why. I had a few tanks of Shell V-Power as you recommended, when prices were 10p lower than today. Now I only use Shell ordinary petrol. I keep revs around 4000-6000 when accelerating and the car feels completely different from when I bought it about 10,000 miles ago.

What has happened? Have I run it in again or has the petrol cleaned out the engine gunk?

Asked on 9 July 2016 by Bigsphinx

Answered by Honest John
Presumably you mean the current shape Civic 1.8iVTEC. Here's my test of one in which I averaged 48.1mpg brim to brim: www.honestjohn.co.uk/road-tests/honda/honda-civic-.../ The Real MPG average is 41.7mpg: www.honestjohn.co.uk/realmpg/honda/civic-2012/ So there must be something wrong. Back to the Honda dealer.
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