[AlanHo]

I did my little test route again this morning because it was sunny and dry - but the air temperature was 7*C.
The route length on the odometer was 41.2 miles (66.3 km), overall time 60 minutes, economy 61.3 mpg (4.61 l/100 km) and overall average speed 41.2 mph (66.30 km/hr)

So for the same route I have achieved :-

64.9 mpg (4.35 l/100km)  41.6 mph (67.0 km/h) air temperature 14*C Dry
62.3 mpg (4.53 l/100km)  40.0 mph (64.4 km/h) air temperature 10*C Dry
61.3 mpg (4.61 l/100km)  41.2 mph (66.3 km/h) air temperature 07*C Dry
60.1 mpg (4.70 l/100km)  40.7 mph (65.5 km/h) air temperature 04*C Damp

It appears to me that temperature does indeed have an effect on economy.

If you extrapolate these figures and assume that the relationship between temperature and economy is linear (It won't be) you get 73.4 mpg (3.85 l/100 km) at 30*C.
The official economy (combined) is 74.3 mpg (3.8 l/100 km) - perhaps the test lab was extra hot that day.......

[bumpkin]

There is no doubt in my mind that air temp is the largest contributing factor to economy if you utilise the same driving methods.

Intercoolers are fitted to maintain an "ambient" temperature and I would suggest that a temp of somewhere between 15-25C is optimum for economy, we unlucky Brits therefore only have a small window of opportunity to get the best economy as shown by Alan's table where he has seen the best figure at 14C. 

Lower temperatures mean the ECU decides that more fuel is required, even for tick-over and as such the economy drops, in the i30 1.6 petrol in Winter I often saw my average drop below 30mpg and even the 1.4 petrol ix20 will drop below 35mpg, my current average in the ix20 with temps hovering between 5-10C is 37.

Like Dazz and Alan, my ix20 is also fitted with low resistance Continental tyres and she is also less keen to "run away" in the wet.

[Phil №❶]

I was thinking like Bumpkin too. The engine is a thermal device after all, so I suspect that a little more fuel is injected by the ECU and there would be a significant amount of heat loss too. On the other side of the coin, the turbo would be compressing denser air, so the power produced should be more, go figure 

[accim]

My fuel economy is worse when it's let's say -10°C then when it's around +20°C. The car (oil..) needs more time to warm up and while it's cold it uses more fuel. In summer i have around 6.2-6.3 lit /100km and in winter 6.8-6.9 lit /100km. The engine is 1.6 CRDi 116hp, but there's a lot of city and highway driving, so that's the reason why it's so high. Though even fast highway driving is much friendlier to fuel economy, comparing it to the driving around the city.

PS: The car looks beautiful on those pictures. And so does the location, where the pictures were taken 

d3matt: Wait for at least 5.000 km. I just found a video clip, of my i30, which was taken when the car had 2.500 km on the clock. There is this straight section of the highway, where I "test" and compare the cars. That way, I get the best results. Anyways, I was testing acceleration and top speed in 6th gear and the results are very interesting. For example, the biggest difference I saw was acceleration after 180 km/h. The car barely reached 190 km/h and then slowly gained another 2 km/h, so that means, that at that time, the top speed was 192 km/h. I see I was holding the throttle (max) and it didn't move a bit. But after a while (@ around 5.000 km and later on), the car gained speed much faster and was able to reach 197 km/h on the same section without any problem.

[Asterix]

Colder air should be better than warm air, if I remember correct from the school days of my mechanic apprentice time. If warm air should be better, why would they fit the intercooler on all diesels..

But the much nicer temps in OZ gives the benefit of not having those cold starts that we vikings face every winter.

I was under the impression that a few of our members have mentioned that their diesels are less economic in the winter.  I know my previous i30 was.

Mine too. But the cold starts at minus degrees and the following longer warm up period cost a lot of fuel. No doubt the engine runs best at the normal operating temperature - 90 C - but the colder air gives the engine a better combustion.

[d3matt]

One other thing I only noticed yesterday is that the speedo goes up to 160mph.  Even cars I've had in the past that could do a much higher top speed than the i30, the speedo normally only went to 140mph.  Makes you wonder what models are in the pipeline! 

[AlanHo]

You only posted that picture to make me feel inadequate about my fuel economy................

[Shambles]

You only posted that picture to make me feel inadequate about my fuel economy................

I can unmask the photoshopping he did...

[d3matt]

Alan - Yes. 

Shambles - I'm not 'that' good at graphics on the computer.  It was a genuine photo, while driving down the M40 tonight.  However, I had only just reset the mpg a mile or two before!

[AlanHo]

More info on gear change points for my new 2012 i30 1.6 CRDi 128PS changing up when the indicator comes on for each gear.

1st  At 2300 rpm = 13 mph (21 kph) change to 2nd - revs drop to 1300 rpm*

2nd  At 2200 rpm = 22 mph (35 kph) change to 3rd - revs drop to 1300 rpm*

3rd  At 2100 rpm = 37 mph (60 kph) change to 4th -  revs drop to 1500 rpm

4th  At 1900 rpm = 46 mph (74 kph) change to 5th -  revs drop to 1600 rpm

5th  At 1900 rpm = 55 mph (88 kph) change to 6th -  revs drop to 1600 rpm

6th  At 2000 rpm = 69 mph (111 kph) approx legal maximum UK and Australia

*Note : It is difficult to be precise about the gear change point in the lowest 2 gears because the car is accelerating more quickly and the low gear ratios gives it extra umph.
            Hence the car gains extra revs after the indicator comes on by the time you actually change gear (reaction time)

[Dazzler]

 

[Doggie 1]

It makes sense re the cool weather. Just look at how much better engines run at night time.
Anyone who has ridden motorbikes (air-cooled) will know that they are much sweeter running on a cool night than on a warm day.

[AlanHo]

I did a return trip from home (Solihull) to Witney near Oxford vis the M42, M40, A34 and A40. The overall distance was 132 miles - 66 miles each way.

I refuelled the car last evening and this was the first journey on the new tank - hence at the start the fuel economy trip was zero

There were two of us in the car taking some folding tables and a large gazebo down to some pensioner friends who want to borrow them for a garden party they are holding in a few weeks time when they get married. Hence the car was about 110 kg heavier on the way down than on the way back.

Going down at lunch time it was dry, no wind and the temperature was 12*C.
Trip time 71 mins = 56 mph (90 km/h) overall average
Trip economy showed 64.2 mpg (4.4 l/100 km)

Return trip in the evening. Dry, no wind, temperature 7*C
Trip time 73 mins = 54 mph (87 km/h) overall average
Trip economy showed 63.7 mpg (4.4 l/100 km)

Note that I did not zero the trip before the return journey - I do this only when I refuel the car and brim the tank.
Yet again temperature seems to have been a significant factor. The car was 110 kgs lighter on the return journey and average speed was about the same - hence I would have expected it to show better economy . However, the economy trip figure had been reduced on completion of the return journey which means the economy on the return was a little worse than on the drive down. I estimate by about 1 mpg

 It so happens that the route I took covers most of the route that Matt uses to commute to work - as he mentions in his post No 46 in this thread. However - despite a much lower average speed than Matt - I didn't achieve the preliminary economy figures he quoted. My lead boots are therefore open to reasonable offers........

[d3matt]

I had to drive my Ceed today as I've still not sold it.  The drive was only for 3 miles and therefore a cold engine all the way, but it instantly felt lively compared to the i30.  However, the i30 has grown on me and certainly feels higher quality. But it should do as it is the newer model.

[Phil №❶]

Hence the car was about 110 kg heavier on the way down than on the way back.

I just love the way no details are left out, I take it you weighed the load 

Great report Alan, and I must say I'm getting frustrated by your continuous supply of information. I'm trying to get l/100 fuel figures from my wife's car, but she keeps filling up without me, doesn't brim or reset the trip comp. It's happened twice and takes 2 weeks or more to use a tank. It's been on 5.6 for the last 3 weeks.

I tell myself, Don't stress, don't stress, don't stress 

BTW, the only thing I can think of regarding you fuel consumption would be the density of the cool air. Even though there was no breeze, the car still has to displace the air it travels through. Perhaps one of our aviators can tell us how much effect this would have. On the flip side though, the turbo should have been working more efficiently and the car was lighter, so 

I did a return trip from home

You are trying to compare two different trips; one out and one back. The terrain in one direction is not equal to that going in the other direction.

[Dazzler]

I did a return trip from home

You are trying to compare two different trips; one out and one back. The terrain in one direction is not equal to that going in the other direction.

Good point Pip .. No doubt Alan will have an answer to that..  (used his GPS for Altitude tests maybe) 

[AlanHo]

Good point Pip .. No doubt Alan will have an answer to that..  (used his GPS for Altitude tests maybe) 

I agree that the trip profiles will differ (almost a mirror image give or take a few cms) - but the number of hills, minimum elevation and maximum elevations will be identical. What goes up must come down etc.

These are the vertical profiles for the two trips taken from my Sat-nav which Dazz accurately predicted were available.

That's exactly my point, uphill on the way out and downhill on the way back (overall) and it's almost guaranteed that going up and down a hill one way is not going to use the same fuel going the other way unless the topography of the hill is identical both ways. Like I said, two different trips. That you got similar (or different) economy each way is irrelevant.

What you need to do (and have of course other times) is to compare trips that include an out and back as one data point.

No?

BTW, I'm pleased that you are getting excellent economy with the new car.

[AlanHo]

I just love the way no details are left out, I take it you weighed the load 

I'm afraid I cheated.

The gazebo was back in its original boxes which were marked by the manufacturer with the weights.

The metal poles, fittings and guys were in one box marked 56 kg.
The canvas roof and sides were packed in the second box marked 42 kg
I am guilty of guessing the 4 folding chairs at 3 kg each
Hence the total came to 110 kg.

Mind you, I sweated a bit humping it from the garage to the car so I suppose I should really have deducted 1Kg for the perspiration I lost......

[AlanHo]

That's exactly my point, uphill on the way out and downhill on the way back (overall) and it's almost guaranteed that going up and down a hill one way is not going to use the same fuel going the other way unless the topography of the hill is identical both ways. Like I said, two different trips. That you got similar (or different) economy each way is irrelevant.

What you need to do (and have of course other times) is to compare trips that include an out and back as one data point.

No?

BTW, I'm pleased that you are getting excellent economy with the new car.

Fair comment Pip - As you saw from the profile my home is 150 feet lower than the destination.
The outward journey thus averaged an uphill slope of 1 in 2320
And the trip home averaged a downhill slope of the same amount.
Hence - other things being equal - you would expect the return journey to use less fuel - particularly because the car was much lighter on the way back.  However - it actually used more fuel.

I recognise that although each journey contained exactly the same peaks and troughs - the steepness of each change varied. A steep uphill climb in one direction and a slow descent - would be a slow climb and steep descent in the opposite direction which may require a different fuel burn. I was just hoping that the law of averages worked in my favour regarding the overall effect of the peaks and troughs. Hence I attributed the different fuel economies to temperature.

It's all by guess and by God anyway - I have yet to prove that the trip economy recorder is accurate and consistent. I know that the odometer reads 1.8% slow.

However the car is quite definitely overall more economical that my previous i30 when you calculate the figures from brimming the tank each time.

I brimmed the tank on collecting the car with just 8 miles on the odometer
At 367 miles I brimmed the tank with 29.9 litres = 54.1 mpg (5.22 l/100 km)
At 739 miles I brimmed the tank with 33.35 litres = 55.2 mpg (5.12 l/100 km)
At 1391 miles I brimmed the tank with 55.57 litres = 53.1 mpg (5.32 l/100 km)

This compares with my previous i30 which averaged 49.01 mpg (5.76 l/100 km) over 13,000 miles and my previous Audi A3 2.0 TDi which averaged 47.1 mpg (5.99 l/100 km) over 36,000 miles.

What does please me (am I allowed to be smug?  ) is that months ago before I ordered the car I published on the forum my estimate of its overall cost of ownership over 5 years compared with the petrol car. I assumed the new diesel car would average 55 mpg over the life of the car despite the official combined figure of 74.3 mpg. My car seems to be performing to my prediction.

Hence - other things being equal - you would expect the return journey to use less fuel - particularly because the car was much lighter on the way back.  However - it actually used more fuel.

By any reasonable allowance for error it used the same. I realise I'm arguing against myself here but my point was not related to absolute economy figures but whether "all things were equal" enough to draw such a fine conclusion. As I said, sounds like the figures are finally going your way but you have a way to go before you do as well as I do. 

4.5l/100km for current tank nearly empty.  I'm pretty certain that my average/top speeds are significantly less than your though.

[AlanHo]

Hence - other things being equal - you would expect the return journey to use less fuel - particularly because the car was much lighter on the way back.  However - it actually used more fuel.

By any reasonable allowance for error it used the same. I realise I'm arguing against myself here but my point was not related to absolute economy figures but whether "all things were equal" enough to draw such a fine conclusion. As I said, sounds like the figures are finally going your way but you have a way to go before you do as well as I do. 

4.5l/100km for current tank nearly empty.  I'm pretty certain that my average/top speeds are significantly less than your though.

As a point of interest - what are the average air temperatures in your location? I can get 4.5 l/100 km out of this car on a long motorway trip - but throw in more than 10% town driving and it deteriorates.

High teens, low 20s for the current tank. Getting into Winter it will be downright cold by Oz standards. Plenty of 14 and 15 max with min never really below zero but close a few times.