Fuel

[Rob™]

29.3 for my 2.7 987.1... yeah, was about 10% lower last winter, this one seems a bit milder (so far).

[DaveEFI]

15 hours ago, zcacogp said:

Whoosh - that's thirsty! 2.7 Gen1 Manual here and mine is currently showing 30.5mpg. And I live in London ....  

You certainly ain't doing London only driving at 30.5 mpg. That is the sort of figure you get cruising a motorway. And if you don't reset the MPG, you get the average for all your driving.

[zcacogp]

@DaveEFI - true, I'm stirring things a little! That's the average across the last 4 or 5 fill-ups which have included a couple of motorway drives. I think I see mid-20's in purely short distance London driving. Actually starting the thing on a cold morning uses a lot of fuel; the range after starting is sometimes 12 or 15 miles lower than when it was last turned off. 

[DaveEFI]

If you want to see your true MPG on a London journey, you need to zero it before starting off. You'll likely get a nasty surprise.😀

[zcacogp]

Yes .... which is why I don't zero it before every trip! 

[Andy9376]

On 2/26/2020 at 6:52 PM, zcacogp said:

Tracking MPG is a good idea but you need to do it for a long period of time to make any meaningful conclusions. Logging the type of journeys done since fill-up is also necessary as cars will do better on longer trips. And an accurate MPG measure is always brim-to-brim when filling; don't rely on the instruments in the car as you have no way of knowing how accurate they are. 

FWIW I did this for a number of years with my old car (944 S2) and it always returned about 10% less MPG in the winter than in the summer. The explanation is that colder air is denser and thus harder to push out of the way when moving down the road, so the engine has to work harder to maintain speed. A car will often be fractionally livelier in colder weather as well as the denser air allows more fuel to be burned in each combustion cycle, meaning potentially more power if you want to use it. 

(I also tracked the difference between Super Plus fuel and regular and discovered that Super Plus gave me about a 10% increase in fuel economy. Given that it costs about 5% more this made it a cheaper option, as well as needing to refuel less often.) 

If you are down 60miles on a tank at this time of year I'd be asking what else has changed in the car - the new tyre (singular? Surely you'd change them in pairs?) would be a good starting point. Check the pressure in it, and in the other tyres as well. 

Thanks for this. I actually did just change one as they were ‘relatively’ new, but it does seem to coincide with the timing of this. 

[Paul P]

FWIW - if you have PCM the trip runs a different "calc" to the overall MPG number - one of the 3 or 4 trip types is " current " - I think it auto resets if you have been parked up for a few hours ( like my Audi ) - so you can see the MPG on the way to work and the way home and the way to cafe/pub/gym/opc/whatever you do for fun.

[msc545]

Check tyre pressures, and ALSO check for dirty air filter.