In ny experience, having driven ny GreenLine Estate for some 10000 miles now (bought it used at 25000 miles), the mpg depends on a wide range of factors.

It only tales a few accelerations or overtaking other cars to significantly lower mpg and never recover from it unless you make a very long journey.

Most economic motorway speed seems to be 55-60mph (60-65mph on the speedometer), above that mpg sinks sharply. Simply changing the cruise control one or two mph up or down makes a big difference.

Loaded or unloaded makes a huge difference. Just one passenger lowers mpg by 10-15%.

Heavy rain and wet roads is the worst, mpg goes down by 20-25%, especially on motorways.

AC or no AC makes a difference, too. Not so noticeable on longer trips, on shorter trips very much so, but usually no more than 5-10%.

In any case, it's the driver, not the engine, that results in good or bad mpg.

Edited 5 October, 201312 yr by jankph

the other one I noticed coming back from Birmingham was I was on headlights all way home and got 80.5 mpg as opposed to the 93mpg going up

 

on the couple of times I have done that run it has been around the 90mpg in daylight so lights seem to affect mpg by about 10%

This is of general truth, I observed exactly this on my Seat (1.6 tdi) except that accelerations and overtakings can be recovered in few kms.

 

In ny experience, having driven ny GreenLine Estate for some 10000 miles now (bought it used at 25000 miles), the mpg depends on a wide range of factors.

It only tales a few accelerations or overtaking other cars to significantly lower mpg and never recover from it unless you make a very long journey.

Most economic motorway speed seems to be 55-60mph (60-65mph on the speedometer), above that mpg sinks sharply. Simply changing the cruise control one or two mph up or down makes a big difference.

Loaded or unloaded makes a huge difference. Just one passenger lowers mpg by 10-15%.

Heavy rain and wet roads is the worst, mpg goes down by 20-25%, especially on motorways.

AC or no AC makes a difference, too. Not so noticeable on longer trips, on shorter trips very much so, but usually no more than 5-10%.

In any case, it's the driver, not the engine, that results in good or bad mpg.

 

the other one I noticed coming back from Birmingham was I was on headlights all way home and got 80.5 mpg as opposed to the 93mpg going up

 

on the couple of times I have done that run it has been around the 90mpg in daylight so lights seem to affect mpg by about 10%

 

Is that calculated (Phone App, or Fuelly) or reading the wildly inaccurate Maxi-Dot display???

my figures are from the multifunction display, I do track the fuel on a spread sheet and find the display compared to tank on tank figures rarely vary more than 2% ,so I have not reason to dispute the trip computer figures on each run

 

the one thing I do notice is the higher the MPG it is slightly less accurate, I assume due to the smaller amount of fuel being measured in relation to tolerances

It's a bit basic to say the difference in economy was having your headlights on.

 

What if you had a 10mph tail wind the whole way there and then drove into a 10 mph wind all the way home?

 

I'd be willing to bet a substantial sum (at least a quid) that driving into a 10mph wind uses more fuel than switching your lights on...

Is that calculated (Phone App, or Fuelly) or reading the wildly inaccurate Maxi-Dot display???

it is sufficient to make full tank and reset the trip km counter each time: you know the litres, or gallons, and the kms, or miles, you just divide this...the only matter is you have to  make full fuel and reset the trip length counter (or make differences and sum, but it's boring and tricky).

 

Obviously it is better to do at least 3/4 tank and averaging several times...

It's a bit basic to say the difference in economy was having your headlights on.

 

What if you had a 10mph tail wind the whole way there and then drove into a 10 mph wind all the way home?

 

I'd be willing to bet a substantial sum (at least a quid) that driving into a 10mph wind uses more fuel than switching your lights on...

 

You're definitely correct there. I measured this for fun earlier this year when I did a 50-mile trip mostly on motorway, knowing there would be headwind going out and tailwind going home. Result: cruising at 59mph and averaging 74mpg going out (95km/h and 3,8L/100km), cruising at 64mph and averaging 76mpg going back (105km/h and and 3.7L/100km).  

Edited 7 October, 201312 yr by jankph

Saturday night & running downhill with the traffic flow for 5 miles into Glasgow i was doing so well.

then a tailgater annoyed me and all that fuel saved was used in one hard acceleration.