New Car #2: Fuel Efficiency

mazda3displayThis is the second article in my current series on my new car – a Mazda 3 SP25. Since the original article released in July, I have since expanded the series to a total of fire articles:

  1. New Car #1: Novated Leasing
  2. New Car #2: Fuel Efficiency  (this article)
  3. New Car #3: Two Months In
  4. New Car #4: Good Bye Subaru Impreza
  5. New Car #5: GPS Navigation System Comparisons

Just this morning, the topic was broached at the breakfast table, and a simple high-level comparison was conducted to understand the fuel savings that I am beginning to appreciate, now that the car is some 18 days old, and I have filled up the tank for the first time using the fuel card system.

A quick disclaimer – I have a very limited understanding of car technical details, so this article is being written from a lay user’s perspective, and the focus is accordingly at the non-technical aspects of vehicle fuel efficiency. The basis for the detail later on is my logbook app which I have maintained for many years now.

Part of the motivation for selecting the Mazda 3 as my next car is reflected in the various reports that have touted its improved fuel efficiency – this one written up on caradvice.com: Mazda 3 to be 30% more fuel-efficient, offer advanced safety tech. The simple comparison done at the breakfast was based on the size of the fuel tanks – my previous car, a Subaru Impreza RS, has a fuel tank capacity of 60L. In contrast, the Mazda 3 is a smaller 51L, and thus every full tank of petrol that I purchase automatically is 9L less. Based on my driving habits, I tend to fill up a full tank every 15 days, or 26 times a year. Assuming this frequency of refueling remains constant with the new car, that’s a savings of 360L of petrol annually. Here in Melbourne, Australia, today’s average unleaded fuel price according to the RACV website, is $1.495 per litre. Applying this to the 360L and that’s slightly over $538 savings!

The big factor which contributes to this savings, is that the Subaru Impreza is an all-wheel-drive (AWD) manual transmission, whereas the Mazda 3 is a front-wheel automatic. It is to be expected that a key difference between these two types of drive transmissions will be seen in the fuel efficiency ratings. Further, the second big factor that makes comparisons of the two vehicles somewhat biased is the number of gears and the gear ratios that they govern. The Subaru, has five gears whereas the Mazda has six. In simple terms, the more gears a vehicle has, the smoother the driving experience can be, with each speed aligning more closely to an optimal gear. Just think of it from a bicycle riding experience – when you change gears, there is an automatic change in the amount of effort required to pedal.

My dad has been driving the Subaru Impreza in recent days whilst we still have it, and he was reminded that when he first bought it in 2005, the fuel consumption is a reflection of the gear ratios designed into the vehicle. The Subaru The approach to our home from the main road has an up-hill gradient, and this is a popular and easy test of vehicles and their gear ratios. The Subaru will accelerate up the hillside but either at a high second gear or low third gear – the speed is in between such that neither gear is optimal. So, even when taking the difference in driving styles – my Dad versus myself – the Subaru is inherently designed to consume more fuel. After all, the Subaru Impreza is a wanna-be WRX, so the sporty-ness feel is engineered intentionally.

The dashboard of the Mazda 3, as seen in the top image, reflects the current generation/standard of providing metrics/counters on the right, allowing the driver to gain a real-time understanding of their car:

  • Current fuel efficiency
  • Overall fuel efficiency
  • Range
  • Cruise control speeds
  • Cruise control fuel efficiency

I personally find the range metric invaluable and I use that, in conjunction with the actual fuel gauge to determine when to fill in with petrol. Previously, my driving behaviour in the Subaru was determined by the fuel gauge and odometer trip readings, whereby a 500km trip distance was for me the trigger to go and fill up with petrol. The range metric available to me now is an inverted reverse approach to my previous behaviour, and it is taking me a little time to adjust and no longer have 500km as the trigger.

The table below is exported out of the app Logbook, which I have found very useful over the 5 years that I have consistently been using it to  track fuel purchases, and also the periodic car maintenance. The beauty of WordPress with the EasyTable plugin allows me to simply upload the file to XBOP and present it as is below. It also provides an interesting historical view of fuel prices over the period. Logbook itself calculates the Efficiency metric, and I added on the Days and KM/Day columns to the end as some basic analysis. Before launching into the detail, I will provide the summary average metrics and notes first:

  • 113 log entries, with two missing from the month of May 2014
  • Average fuel price is $1.35/L
  • Average fuel efficiency is 9.96L (per 100km)
  • Average tank of fuel lasts 15.3 days
  • Average amount of fuel purchased each time is 47.07L
  • Average cost of fuel purchase on average is $63
  • Average distance driven per day is 33km
Date Odometer Trip Fuel Cost Litres Price/L Efficiency
3/10/2009 26,361 400 48.1 37.9 1.269 9.48
18/10/2009 26,756 395 53.07 42.15 1.259 10.67
3/11/2009 27,170 414 55.06 45.54 1.209 11
18/11/2009 27,593 423 57.58 46.14 1.248 10.91
1/12/2009 28,063 470 60.45 47.79 1.265 10.17
15/12/2009 28,580 517 64.01 51.66 1.239 9.99
29/12/2009 28,998 418 54.18 44.45 1.219 10.63
12/01/2010 29,436 438 52.09 45.02 1.157 10.28
25/01/2010 29,901 465 60.66 47.06 1.289 10.12
10/02/2010 30,301 400 52.33 42.93 1.219 10.73
28/02/2010 30,800 499 61.02 54.78 1.114 10.98
15/03/2010 31,288 488 65.95 47.48 1.389 9.73
3/04/2010 31,764 476 70.9 51.79 1.369 10.88
21/04/2010 32,114 350 53.19 41.72 1.275 0
2/05/2010 32,570 456 60.63 43.34 1.399 10.55
23/05/2010 32,982 412 67.66 48.71 1.389 11.82
8/06/2010 33,385 403 54.44 45.03 1.209 11.17
23/06/2010 33,811 426 59.49 46.88 1.269 11.01
10/07/2010 34,248 437 60.86 48.73 1.249 11.15
28/07/2010 34,687 439 59 47.24 1.249 10.76
14/08/2010 35,131 444 59.41 47.95 1.239 10.8
28/08/2010 35,624 493 61.18 51.03 1.199 10.35
12/09/2010 36,112 488 55.96 49.13 1.139 10.07
25/09/2010 36,617 505 66.74 49.11 1.359 9.73
6/10/2010 37,061 444 47.76 43.22 1.105 9.73
19/10/2010 37,533 472 55.05 45.53 1.209 9.65
31/10/2010 38,021 488 57.88 47.48 1.219 9.73
15/11/2010 38,468 447 57.29 47 1.219 10.52
29/11/2010 38,941 473 63.51 46.39 1.369 9.81
8/12/2010 39,394 453 51.5 42.95 1.199 9.48
21/12/2010 39,821 427 54.25 43.09 1.259 10.09
28/12/2010 40,171 350 41.15 35.81 1.149 0
10/01/2011 40,613 442 54.73 46.42 1.179 10.38
27/01/2011 41,076 463 58.04 45.03 1.289 9.73
10/02/2011 41,546 470 63.06 49.69 1.269 10.57
21/02/2011 42,043 497 65.01 48.55 1.339 9.77
9/03/2011 42,433 390 60.38 41.67 1.449 10.69
21/03/2011 42,850 417 60.81 40.57 1.499 9.73
3/04/2011 43,258 408 58.64 42.52 1.379 10.42
17/04/2011 43,736 478 61.09 46.46 1.315 9.72
2/05/2011 44,189 453 61.99 44.95 1.379 9.92
17/05/2011 44,519 330 52.99 36.93 1.435 0
30/05/2011 45,006 487 66.41 48.16 1.379 10.41
13/06/2011 45,509 503 65.51 49.67 1.319 9.88
25/06/2011 45,981 472 73.67 48.5 1.519 10.27
6/07/2011 46,438 457 66.99 46.55 1.439 10.19
17/07/2011 46,894 456 63.02 44.41 1.419 9.74
31/07/2011 47,384 490 61.67 48.98 1.259 10
14/08/2011 47,820 436 64.31 45 1.429 10.32
31/08/2011 48,285 465 60.34 46.1 1.309 9.91
17/09/2011 48,781 496 70.65 51.61 1.369 10.4
8/10/2011 49,278 497 72.03 51.49 1.399 10.36
30/10/2011 49,777 499 67.01 48.24 1.389 9.67
13/11/2011 50,173 396 48.16 36.24 1.329 9.15
28/11/2011 50,604 431 61.12 46.69 1.309 10.83
10/12/2011 51,081 477 65.83 46.07 1.429 9.66
26/12/2011 51,450 369 52.56 42.42 1.239 11.5
30/12/2011 51,874 424 52.19 36.522 1.429 8.61
4/01/2012 52,373 499 56.88 44.82 1.269 8.98
22/01/2012 52,801 428 70.26 47.83 1.469 11.18
8/02/2012 53,269 468 62.32 48.35 1.289 10.33
27/02/2012 53,726 457 70.52 49.7 1.419 10.88
19/03/2012 54,175 449 67.67 48.37 1.399 10.77
4/04/2012 54,633 458 67.26 45.48 1.479 9.93
19/04/2012 55,037 404 62.48 41.68 1.499 10.32
6/05/2012 55,529 492 74.29 50.92 1.459 10.35
21/05/2012 56,018 489 72.56 51.28 1.415 10.49
7/06/2012 56,510 492 75.32 52.71 1.429 10.71
24/06/2012 56,970 460 66.35 50.3 1.319 10.94
6/07/2012 57,418 448 58.54 46.13 1.269 10.3
18/07/2012 57,915 497 61.89 49.95 1.239 10.05
28/07/2012 58,369 454 62.34 48.51 1.285 10.69
12/08/2012 58,861 492 71.58 51.53 1.389 10.47
27/08/2012 59,297 436 67.17 48.15 1.395 11.04
17/09/2012 59,732 435 61.8 47.36 1.305 10.89
4/10/2012 60,203 471 66.67 48.14 1.385 10.22
17/10/2012 60,665 462 66.07 46.89 1.409 10.15
29/10/2012 61,121 456 64.18 44.91 1.429 9.85
10/11/2012 61,595 474 63.39 45.64 1.389 9.63
28/11/2012 62,005 410 56.38 44.43 1.269 10.84
15/12/2012 62,488 483 62.88 48.78 1.289 10.1
29/12/2012 62,966 478 63.65 51.37 1.239 10.75
22/01/2013 63,395 429 58.65 46.96 1.249 10.95
7/02/2013 63,838 443 69.04 44.57 1.549 10.06
1/03/2013 64,186 348 55.24 40.77 1.355 11.72
12/03/2013 64,656 470 71.95 46.15 1.559 9.82
27/03/2013 65,101 445 63.62 45.8 1.389 10.29
14/04/2013 65,563 462 64.33 45.98 1.399 9.95
26/04/2013 65,970 407 66.14 55.63 1.189 13.67
13/05/2013 66,437 467 62.98 48.48 1.299 10.38
31/05/2013 66,874 437 69.46 48.95 1.419 11.2
16/06/2013 67,373 499 72.37 53.25 1.359 10.67
30/06/2013 67,871 498 76.56 53.95 1.419 10.83
15/07/2013 68,349 478 76.97 50.67 1.519 10.6
28/07/2013 68,834 485 78.66 50.78 1.549 10.47
10/08/2013 69,269 435 62.44 44 1.419 0
25/08/2013 69,739 470 68.07 49.72 1.369 10.36
8/09/2013 70,229 490 68 49.67 1.369 10.14
24/09/2013 70,682 453 70.36 47.25 1.489 10.43
7/10/2013 71,146 464 68.72 46.15 1.489 9.95
22/10/2013 71,616 470 61.58 45.99 1.339 9.78
2/11/2013 72,088 472 72.17 49.13 1.469 10.41
15/11/2013 72,524 436 59.05 45.81 1.289 10.51
26/11/2013 72,970 446 58.23 44.15 1.319 9.9
16/12/2013 73,477 507 82.98 54.99 1.509 10.85
4/01/2014 73,988 511 81.62 54.09 1.509 10.59
20/01/2014 74,492 504 73.57 49.41 1.489 9.8
2/03/2014 74,891 399 65.82 46.55 1.414 11.67
3/04/2014 75,393 502 87.54 60 1.459 11.95
15/04/2014 75,843 450 71.5 46.16 1.549 10.26
1/06/2014 77,235 1,392 74.1 49.5 1.497 3.56
15/06/2014 77,689 454 66.92 46.83 1.429 10.31
6/07/2014 78,127 438 69.55 49.36 1.409 11.27

The following graphs were produced via Excel, split into groupings which make for easier comparison.

LogbookMetricsThe clear upward trend in the fuel cost/price is not as alarming and reflects the tempering of fuel prices in recent times. The one exception in early 2014, where 60 litres of fuel was purchased reflects the one incident where I completely ran out of fuel… The days/duration metric is also slightly out for 2014, where I spent an entire month on holiday – the only extended holiday in the timeframes covered by this data set! The clear relationship between fuel cost and litres is the price – the bottom line which is pretty meaningless in this overall graph.

FuelCostLitresDuration

 

 

 

 

This second graph helps to make clearer the rising cost of fuel. Across the board, my fuel purchasing habits and frequency is steady, within a range of 2-3 weeks, spending a similar amount of money on a similar amount of fuel. The data for 2014 after April is distorted because of the missing month of May data…

FuelPriceEfficiency

A brief analysis of the fuel price and efficiency graph above first requires us to ignore the four/five efficiency points where the data is simply not available. June 2013 has one spiking of efficiency. A slight trend was emerging towards the end of 2013 and throughout 2014.

This dataset is exclusively for the Subaru Impreza. Whilst my Dad continues to drive it, I have agreed to continue logging it via these tools for analysis. Naturally, the daily distances driven will decrease dramatically, and the time between refuelling will lengthen.

Part three of this series will thus not become available until the final logs are recorded for the Subaru. Planning ahead, part four of this series will likely be scheduled for December 2014, to allow for a six month period of data to be logged.

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