Boring question: 987 trip computer

[kingston12]

Can anyone confirm what aspect the mpg readout on the dash of a 987.1 Boxster actually shows? I had assumed that it is average mpg since last reset, but mines seems to stick after a certain amount of miles and continues to give the same readout whether I am doing a constant 70 on the motorway or driving along a nice B-road.

After a reset it works fine again for a while and then stops again later on.

[Ice White Socks]

Mine shows cumulative average MPH since the last reset. Surely after a few weeks it will settle to its long term average and it will take more than a quick thrash to move it (mine for example hasn't been reset for about 6000 miles and stays nailed to 28.3 whatever happens). Similarly my one series BMW hasn't been reset since new- it started at 52.3 average- jumped to 53.3 average after 10k and hasn't moved since (now coming up to 50k!!).

[kingston12]

I would expect it not to move after a few weeks, but this is much quicker than that. I reset mine this morning, and the mpg was constantly changing for the first 50 miles or so and then completely froze. When I went on a motorway later it still stuck at the same figure even after 15 miles of driving around 70. I then reset it and it started to give a more realistic figure.

[Magic919]

As it is a running average, you'd expect it to move around a lot just after a reset and then get more settled as time goes by.

[kingston12]

Magic919 said:

As it is a running average, you'd expect it to move around a lot just after a reset and then get more settled as time goes by.

I would, but it just stops dead after about 50 miles and then never moves again until reset. I guess it must be faulty on mine then if others work. Still, I am not complaining if that is the worst thing that goes wrong on the car!

[cslwannabe]

I used to reset mine every tankful and for the first 5 miles or so after resetting it would give a wildly optimistic figure - typically 40mpg, but soon settles down to 27ish. Mine is typically 1 mpg optimistic but I'm a bit worried my mpg is still 25-26ish following little use during the winter whereas previously it was more like 27-28 and was even as high as 29mpg on my motorway trip back from Revolution following its service in December.

[K1909]

I usually reset mine after every fill, and my journeys vary from stop start traffic for 2 weeks and then some longer distance motorway driving. Mine still changes even after I've done a good 200 miles, and rose yesterday from 23 to 27.4 after a 100 mile motorway drive sitting between 60 -70ish.