I have also just replaced the spark plugs, and that's definitely made a difference! Although the old ones looked pretty clean, I don't think they had been changed for a long time, possibly ever. I also treated the underside with a coat of Lanoguard.
Yesterday I did a long motorway drive on my commute back, with speeds limited to 60 mph (and 50 in some parts), and the on-board computer very optimistically reported 61 mpg, which was definitely an overestimate. This morning, with some start-stop traffic and a long stretch at 70 mph, the computer settled on 54 mpg, which I am still really happy with, considering that the same journey was getting me 46-49 mpg before replacing the plugs. I will crunch the numbers for actual mileage and fuel consumption at some point to get a proper estimate.
At this point, I think the awful tyres are probably the bottleneck for fuel economy, but replacing them at this point would be very expensive and not really justifiable, since they have done less than 3000 miles.
So further fuel savings will have to wait. My next job is to find a good dashcam, as yesterday a lunatic hit and nearly took out my side mirror on a country road on my way to work (the motorway was at a standstill due to an accident), and they failed to stop!
That's a topic for a different thread, though
