To Pompeii. With echoes of Trafalga. by Jumper

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To Pompeii. With echoes of Trafalgar.

Off to Portsmouth on Tuesday to celebrate one’s birthday with a visit to HMS Victory. Can’t wait, always wanted to see it (with both eyes). Doing an overnight so that
a certain amount of shopping can take place without rushing - the dockyard that is, the shopping usually goes by in a blur anyway. Note to self: don't take her anywhere near Specsavers.

First things first: fill to brim, zero all trips, top up to brim on return.

2.5 Auto, approx 240 miles round trip. Can I average over 35 mpg at national limits? Or even prove the Owner’s Handbook is (surprisingly) accurate?

Pedantry is a minor detail for those with nothing left to do. Especially if it's got small print.

Posted 04 May 2012, 18:35 #1 

Tank full to the brim and all trips zeroed, reached 9 o’clock on the temp gauge (and stayed there for the whole trip - more later) within 1.6 miles of reaching crawling traffic in commuter soup lasting about 4 miles.

Then stuck to national limits (for most of the way). Kick-down used occasionally when leaving slip roads to enter m’ways and then Cruise until no longer viable. Portsmouth was busy but no serious hold-ups. Car not used between getting there and leaving to come home so overall consumption I would estimate about midway between ‘extra urban’ and ’combined’.

Filled to brim when back and noted figures:

According to pump, used 39 litres (8.6 galls).
Odometer and OBD (On Board Diagnostics) were identical (!) at 263.1 miles.
Consumption then was 31 mpg.

However, OBD showed average speed of 46mph and consumption of 35.7 mpg! That’s 14% out on mpg! Why would it be so wrong on consumption but entirely accurate on distance travelled?
Coolant temperature: My first week of owning the car 2.5 years ago was partially marred by the thermostat letting go. Fortunately, at an early stage on the temp gauge advance to oblivion, I noticed it and stopped. Yes, I know some would say I’m lucky to get away without collateral, but I always have been . Anyway the dealer who supplied it sent a low loader and a taxi to take me home and arranged a new thermostat and all new coolant. I only mention this because that was the last time I have had to top up the coolant. I do a weekly check, have not had to top up in 2.5 years, and the temp gauge has never exceeded three-quarter mark. Note to self: replace coolant this year. Ho hum.
Actual (brim to brim) v. handbook : MPG - h’book is surprisingly accurate.
Actual v. OBD: rather large discrepancy in mpg but curiously ’miles travelled’ is spot on with odometer - both systems driven by the same source? Also ’range’ on obd - do not trust, depends on which way the wind blows.
Sum up: a large heavy automatic car at speed, in silence, supremely comfortable. Over 30 mpg. Contented wife who dozed most of the way. Stood on the spot where Nelson fell, and with a large (unopened) bottle of Napoleon Brandy safely in the boot. See, told you I was lucky.

Posted 10 May 2012, 15:19 #2