MK7 GTD - Real Life MPG

[corgi]

I get about 44mpg on the way there (with Xenons on and colder ambient temperature) and 48mpg on the way back (without them).

Why would having headlight on make a measurable difference to fuel consumption?

My logic is this.

Even with Halogen headlights the draw would be less than 200 watts (this is way less than your average heated rear window) Xenons draw way less... and the car's output is 135KW. So the electrical draw for running with your headlights on is about 0.15% of the total output.

I can understand that running with aircon on would make a significant difference...

[monkeyhanger]

I get about 44mpg on the way there (with Xenons on and colder ambient temperature) and 48mpg on the way back (without them).

Why would having headlight on make a measurable difference to fuel consumption?

My logic is this.

Even with Halogen headlights the draw would be less than 200 watts (this is way less than your average heated rear window) Xenons draw way less... and the car's output is 135KW. So the electrical draw for running with your headlights on is about 0.15% of the total output.

I can understand that running with aircon on would make a significant difference...

Cruising at 60mph where air resistance isn’t huge is probably only drawing 30kW/40BHP, so that 135W is a little more significant, but still only 0.5% on paper. Poor mpg is almost certainly down to the lower ambient temp that normally accompanies dark nights/morning and the car running colder for longer. Air temp at 7am on a morning recently has been typically 6-8C, gaining 43mpg. This morning at the same time it was 13C and the car did 47mpg on the way to work. Returning home from my commute, the car has done 46-49mpg with ambient temp of 14-20C recently.

[Sootchucker]

Well mine is improving hand over fist. On Saturday night the wife and I went for a meal in Liverpool (about a 16 miles trip each way). Mixture of urban road, "A" roads and fast dual carriageways at 70 and 40mph.

Never even looked at the consumption when we got there, but coming back after a journey of 32miles, we got 58.6mpg (and the return trip was with the wife driving for the first time - and she doesn't hold back).

So if this improvement continues over the next few thousand miles, it will most certainly beat the Rocco for efficiency.

Obviously I don't yet know how inaccurate the computer is, but I guess it's out by about the same amount at the Scirocco, so I'm using the on screen figure from both as a comparison.

[monkeyhanger]

Well mine is improving hand over fist. On Saturday night the wife and I went for a meal in Liverpool (about a 16 miles trip each way). Mixture of urban road, "A" roads and fast dual carriageways at 70 and 40mph.

Never even looked at the consumption when we got there, but coming back after a journey of 32miles, we got 58.6mpg (and the return trip was with the wife driving for the first time - and she doesn't hold back).

So if this improvement continues over the next few thousand miles, it will most certainly beat the Rocco for efficiency.

Obviously I don't yet know how inaccurate the computer is, but I guess it's out by about the same amount at the Scirocco, so I'm using the on screen figure from both as a comparison.

My dad reckons the MFD is about 5% out on his as opposed to 9/10% out on previous models. That could mean for me that 47.5 mpg indicated = 45mpg actual; same as Scirocco indicating 50mpg and only getting 45mpg actual. I’ll let you know when I fill my tank again.

When you say “not holding back” what are we talking here – quick to get up to speed and religiously sticking to speed limits, or getting up to 80mph on the dual carriageways etc? If I stuck to 70mph I would undoubtedly see an improvement, maybe 48mpg at 80mph becomes 53/55mpg at 70mph. Driving the car at similar speeds to the Scirocco (80mph on dual carriageway and quick to get up to speed) is my current mpg yardstick for the GTD, I’ll be happy when I can drive like I did in the Scirocco andd surpass my old economy.

[corgi]

Cruising at 60mph where air resistance isn’t huge is probably only drawing 30kW/40BHP, so that 135W is a little more significant, but still only 0.5% on paper. Poor mpg is almost certainly down to the lower ambient temp that normally accompanies dark nights/morning and the car running colder for longer. Air temp at 7am on a morning recently has been typically 6-8C, gaining 43mpg. This morning at the same time it was 13C and the car did 47mpg on the way to work. Returning home from my commute, the car has done 46-49mpg with ambient temp of 14-20C recently.

True, I talked about 135Kw to emphasise how insignificant the power draw of headlights are. I'm certain that ambient temperature will have a much bigger effect especially with modern, direct injection diesels that tend to run much cooler than indirect engines of the past... And they will run cooler for longer - it can take half an hour in very cold weather to get warm air out of the vents. In some climates they have to specify pre-heaters for diesels...

[monkeyhanger]

Did the exact same trip to the dealership today to sort out those rear suspension transport cones as I did last week to pick up my tax disc. Last week was 53.6 for the round trip and this week was 55.4mpg = a 3.4% increase. I got up to 80mph on the 6 miles of the 30 mile round trip that was 70mph/dual carriageway and religiously stuck to 30/50/60mph the rest of the way (lots of speed cameras). If I’d been saintly at 70 then I’d have probably matched Norbreck’s 58mpg. Considering his is DSG though, I still think he’s doing better than me. The car has opened up a lot – I seem to have access to more torque in 5th and 6th above 60mph. About 450 miles on the clock now.

[Sootchucker]

Good to see that these 184ps engines after a bit of a rocky start seem to be fairing quite a bit better than a number of the 1.6 TDI and 2.0 TDI 150ps units, that seem to be giving a lot of owners headaches with poor mpg at the moment !

[Skinnee D]

I've heard and read some comments from 2.0 TDI drivers that avoiding Eco mode bizarrely improves their mpg, even on a manual. Maybe this could have a similar effect on GTD's?

[Valenni]

I've heard and read some comments from 2.0 TDI drivers that avoiding Eco mode bizarrely improves their mpg, even on a manual. Maybe this could have a similar effect on GTD's?

Don't see the point of buying a GTD for it's ECO mode TBH.

[Sootchucker]

I dunno, if you are on the M25 for instance and stuck in a constant flow of speed camera controlled temporay speed limits, I can see the free wheeling mode for the DSG boxes in Eco mode potentially saving a lot of fuel (disengages the engine from the gearbox when on the over-run, so the car coasts freely with no engine braking slowing it down) ?