In a thread a while back the question of octane ratios came up.
Situation :

Prior to last service  just used normal 91  unleaded (BP) & Gull

Post last service  noticed consumption went up  (over exactly same
routes and driving style )
went up about 1 litre per 100k

So chucked in half a tank of 95  35 litres to 70 litre tank
consumption went not only back to normal but improved slightly ?

ran tank down to 10 litres remaining  refuelled vehicle  to full with
91 and up went the consumption again.
Thought hmmmmmmmm  so refilled next time with 98    consumption only
got worse ???

back to 50/.50 blend of 95/91  it the vehicle is less thirsty and back
to 7.3 7.7 per 100 clicks
on 98 its 10.9!!!!!

Asked the dealer  AVG Perth  what could be going on
only clue he thinks is they change the computer for winter motoring ?
And to parameters for its mileage  ?

He said might be an idea to hook up my in car computers (2 lap tops)
with a program he has  that monitors performance  from the cars
computer system  But is a "bit unofficial"

Given I do up to a 1000 clicks a day  this consumption thing
translates direct to my bottom line .
Any thoughts or comments ?
Cheers