Whether it is just the temperature, or also the fact of driving around with the windows down, this warm weather results in my car sounding like there is a troupe of Irish line-dancers practising under the bonnet. The noise from the valve gear is just annoying. So it was that I chose to buy the higher octane fuel this morning. This is advertised as providing more power and better fuel economy. The first claim is almost without doubt correct, but I never find that the fuel efficiency improves with this fuel; I suspect that the temptation to enjoy the extra power and the lack of feedback about how hard the engine is working negates any expected efficiency improvement.
Whether the EMU actually responds to the temperature to decrease the normally parsimonious ratio of petrol to air, I don't know, but the horrible sound of the pinking engine suggests to me the rattle of an addict, frantic for their next hit of narcotic hydrocarbon. Yesterday's drive home scored 57 miles per gallon, according to what little of the data screen I could read - it fades from the bottom of the display in hot weather. This morning, driving consciously carefully whilst listening for any improvements, albeit in much more humid and cooler air, registered 56 MPG in the carpark. The consumption on the two journeys is not normally exactly comparable in any case, so I can't draw any conclusions except that I noticed some hills which were not so demanding of a gear change this morning and I didn't have to wind up the radio to mask the sound of the engine's DTs.
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