Fuel consumption - Computer v.s. Refill interval

[shyster77]

Greetings Cayenne-mates,

I'd been experimenting with a few styles of driving on an 2006 S, and I find that, while the actual gasoline consumed (as indicated by the miles drives/gallons filled) hovers around 15.8-16.5 (with almost 50/50 Highway/City relaxed driving), the computer (as indicated by the Main Menu>Vehicle Info>Consum) seems to quoting 18.5-19 (as in attached).

I usually fill up x gallons and compare the calculations - is this why? Should a few full tanks be driven, before they both will coincide?

I've never owned a car with a computer that can show mpg, hence curious on the discrepancy here.

Any ideas?

Cheers,

Edited October 22, 2011 by shyster77

[mcbit500]

My GTS consistenly shows substantially lower consumption on the computer than actual.

[shyster77]

Interesting, mcbit500! Did some research and apparently the computer usually logs 2-3 miles under actual in general but allegedly Porsche computers are near -.5mpg to the actual.

Have you found out why yours is the other way?

[mcbit500]

My computer shows an overall consumption 15.9L/100km whilst the actual overall is 16.7L/100km. This is in tune with every other Porsche trip computer I have seen.

[odix]

shyster77 -- double-check your vehicle settings -- the difference you're noting almost matches the volume difference between US gallon and UK imperial gallons as it relates to miles travelled/efficiency/consumption.

Cayenne's (and Porsche in general) tie GPS (if nav eqiuipped) to physical odometer and are usually quite accurate -- they may slightly err on showing more efficiency then reality but not as much as you are seeing.

Below from an '04 Cayenne S owner's manual shows you how to confirm the setting:

Edited October 24, 2011 by odix

[shyster77]

Good point, odix. I just checked the Units for Consumption and it is checked for MPG (US). What is interesting is that the Consumption was showing to be 17.8mpg when I refilled and the actual consumed was 16.31mpg, i.e. the difference is getting closer than, what it showed before at 18.8-19mpg for the consumption, even though the actual remains almost consistent.

The difference still baffles me...

[odix]

Next time you fill-up/refuel reset both MPG counters -- one at the main PCM level (if you have nav) and the other via your center console. It may be you had a run of very good freeway or soft-driving consumption and it's still skewing your averages. If you reset counters you be able to start fresh. I usually reset both counters at each refuelling.

[fredjchavez]

I have found that the computer is optimistic to the tune of 10 or 15%. Ignorance is bliss i suppose! :)