Brilliant mpg - why ?

[Sootchucker]

Did my usual drive home from work last night. Nothing unusual, crawling in the usual spots etc. and the overall time of the journey was around the same as usual (+/- 5 mins), ambient temperature at 10.5 deg C, and when I arrived home, I checked my journey stats, and was surprised to see the best mpg I've ever had since owning the car - 63.4mpg according to the computer. My normal "average" is around the 50-54 mark.

I then noticed that as I'd been messing with VCDS at lunchtime, I'd turned the climate control system completely off using the "OFF" button, and there it had remained. Can the turning off the climate control really account for the difference or was this most likely a fluke ?

[fredgroves]

10 degrees after a day of higher temps should make for an optimum journey... its probably also not trying to heat or cool the car either - even if you hadn't knocked it off.

I noticed last night was a good run for me too btw..

[monkeyhanger]

Unless you're going heavy on the aircon when it warms up a bit, or heavy on the heating (rear windscreen, wing mirrors, heated seats all on together with aircon for demisting), the mpg seems to shoot up above 8C ambient temp on the GTD like no other TDI I have previously owned. Modest use of the preheater to maintain 16C in the cabin at a low fan speed without aircon seems to have no measurable mpg penalty for me when ambient temp is over 5C.

At 12C on Thursday afternoon, coming home from work, I drove the car hard on my 13 mile commute and still got 49mpg, that might've been 38mpg a few weeks ago at 2C on the morning commute.

The cold seems to kill GTD mpg the way it is set up for EU6 compliance (less air in and compressed makes for less heat generated in the compression cycle, poorer mpg for longer while warming up, as well as less generated NOx - probably why the MK7 TDIs take an age to warm up), make the most of the warmer weather.

[Mark V GTD]

I notice this on Friday too - 55mpg on a 35 mile trip (mainly M25 at 5.30pm too). Ambiant temp was 13.5c.

[Dave the Cat]

I suspect we are now coming off the winter diesel mix which has a negative impact on the MPG - roll on the summer 

http://en.wikipedia.org/wiki/Winter_diesel_fuel#United_Kingdom

[fredgroves]

Yes, almost certainly its the winter diesel now you point it out...

[monkeyhanger]

Winter mix doesn't come into it that much, it's only 2% less calorific than Summer diesel (in the UK, where our Winter stuff isn't that far removed from our Summer stuff due to our "mild" winters. Cold starts with low (less than 8C) ambient temp kill mpg, the shorter the journey, the bigger the effect.

[Sootchucker]

Well the good weather is certainly helping my MPG nicely now. With an ambient last night on my way home of 17°C for my usual journey where in winter I was getting around the 50-55mpg mark, last night I got....wait for it... 65.4mpg over 18 miles !

That's the best I've ever had and is only 5% off the advertised Extra Urban figure for my model (2.0 ltr 184PS TDI BMT DSG - 5-door) advertised at 68.9 mpg.

I know my computer in the car reads about 1.5% optimistic, but that should still equate to a real 64.5mpg Unreal for a car with just short of 190hp !

Oh, and I have been doing a "test" over the last few weeks. It been pretty cold most mornings when I set off (at around 6.45am it's been around the 2-5°C mark). So what I have been trying is switching the climate control fully off (by hitting the "OFF" button naturally), and only switching it on when the car's temperature gauge is about halfway between cold and normal, and I have regularly seen an MPG drop of around 4-5mpg for each journey.

I don't know if this is the electric PET heater taking the load or what, but it does make a much bigger difference than it has even done in any of my other cars. The car also seems to warm up between 1.5-2 miles sooner than if would otherwise.

[mcmaddy]

I've just been turning the climate control off but leaving the heating on for my 3 mile journey to work and have been getting 40mpg regularly.

[Cossieian]

I've just been turning the climate control off but leaving the heating on for my 3 mile journey to work and have been getting 40mpg regularly.

Forgive my stupidity but how do you do that