With my father convalescing at my sister’s house in Sydney, Chikako and I have visited him the last two weeks. So I’ve had a few more opportunities to see the effect of various hypermiling techniques and tweaks on fuel consumption (FC).
On 8/07/2012 I did drove the normal run using cruise control set to 114km/h (true 110km/h, officer) some A/C use and a single stop in both directions. “To” trip was, Federal Highway, Hume Highway, M5, Southern Cross Drive, park near Hyde Park, some shopping in the city and then up the Pacific Highway. Return was from Fox Valley Way, Pennant Hills Road, M2, M7, Hume, Federal, home. The numbers were 613.7km at 4.6l/100km (corrected to 4.9l/100km based on 6.5% HSI error) at an average speed of 86km/h.
Since then I replaced the slowly-leaking and basically bald OEM Bridgestone B250 tyre (77,000km ain’t bad, but a nail ain’t good) and one of the Ovation ecovision VI-682 black round things with 2 Bridgestone ecopia PZ-X tyres. I also started using 91 RON fuel.
TOP TIP: Extensive testing by Prius owners has confirmed that anything above 91 RON (or 87 AKI in USA) is a waste of money and often brings higher FC.
Then on Friday 20 July I had an 80,000km service, which is the major service interval for the Prius. I immediately saw an astonishing difference in FC. See below for details
Driving to Sydney and back brings a different set of challengers for hypermiling. For a start, Pulse and Glide techniques don’t seem to be applicable when you need to maintain 110km/h for a few hours. To recap, in May 2012 I stuck with Cruise Control at 114km/h indicated, but then tried a few new ideas. If I changed to PWR mode before steep hills, my speed didn’t drop so much on the way up. This avoided the sudden acceleration that happens in ECO mode as the speed drops way below the set value and the Prius delivers an almighty application of everything in its arsenal. PWR mode seemed to reduce FC on very steep hills by maintaining momentum and gradually increasing the throttle. for example, the very steep climb from the Towrang intersection maxed at 15.5l/100km in PWR mode compared to 17l/100km in ECO mode.
On Saturday 21/7 we were in no hurry to reach Northern Sydney, so the first thing was to not use the cruise control to try a little experiment. (I set it at 114km/h but cancelled it so that I could resume as a fall-back position.) The second thing was to forget any notion of maintaining a steady speed up a hill but instead maintain a steady pedal pressure without touching the PWR zone on the HSI. This takes some forethought: If a car was approaching at speed I flashed my right indicator to invite them to pass and I had to be careful not to squeeze cars entering the highway. There’s not many slow vehicle lanes on the highway except on the steepest hills. On the climb out of Towrang intersection I only reached 9.5l/100km, compared to cruise controlled 15.5l/100km in PWR mode and 17l/100km in ECO mode.
It was a -4°c start. I’ve recently confirmed that the coldest part of the garage, which is near the back of the car where the HV battery lives, bottoms out at 5°c even on long, cold nights. Unfortunately, I haven’t fitted my engine heater, so it was chilly to start. When I entered the Federal Highway the coolant was only at 60°c.
The route was Federal Highway, Hume Highway, M7, M2 to the turn-off at Pacific Highway Chatswood and then to Chatswood shops. There was a few kilometres of road work on the Hume and the M2 was almost entirely under renovation. While 60km/h zones can help FC, that’s more than offset by the rough road surface, twists and turns and lack of momentum in hills that are normally taken at 90km/h.
To my astonishment the FC figures were very good for the whole journey. Canberra to the Mobil at Pheasants Nest returned 195.7km 4.1l/100km (4.36l/100km corrected, 64.8 mpg(Imp) 54.2 mpg(US) 22.94km/l) at 95km/h. Pheasants Nest is about 290m ASL, so there’s still some descending to do.
Even more surprising was completing the trip to Chatswood: 304.2km, 3.9l/100km (4.1l/100km corrected, 68.9 mpg(Imp), 57.6 mpg(US) 24.39km/l) at an average of 90km/h. (See the new blog header) The 107.4km leg from Pheasants Nest to Chatswood used 4.09l at 3.8l/100km (72.4 mpg(Imp), 60.6mpg(US), 25.6km/l) according to the Garmin ecoroute HD.
Eventually I rolled into Turramurra 318.1, 3.9l/100km (4.1 corrected) at an average speed of 77km/h (the traffic from Chatswood was fierce.)
Return was a similarly relaxed affair. Remember, Canberra is 600m ASL and there’s several 750m peaks in the Southern Highlands. This is where the passive hill-climbing technique became interesting. On a particularly long, steep hill I dropped from 110km/h to almost 70km/h. Fortunately there was a slow vehicles lane to retreat to so the other cars had two lanes to overtake.
Turramurra to Marulan was 186.8km 4.8l/100km at 88km/h. ecoroute HD read 185km at 5.0l/100km with 9.3l of petrol used.
After 815km I put 38.02l of BP 91 RON for a tank average of 4.66l/100km. Considering the amount of climbing to get to Marulan at 640m ASL, that’s starting to look pretty good. The leg from Marulan to Home was 114.1km, 4.5l/100km at 95km/h (ecoroute HD 113.1km, 4.7l/100km, 5.31l used).
So, the round trip on Saturday 21/7/2012 was 619km at a corrected 4.56l/100km (62 mpg(Imp) 51.8 mpg(US) 21.93km/l). That compared well against Sunday 8/7/2012, which was 613.7km at a corrected 4.9l/100km (57.6mpg(Imp) 48.2mpg(US) 20.4km/l).
Unfortunately I introduced too many variables (new tyres, major service, 91 RON, new driving techniques) to pinpoint which had the greatest effect on FC. The only one I’m uncertain of is the 91 RON petrol, but since it is 10-20¢ per litre cheaper than 95 RON I could afford to increase FC by almost 10% and still be in front.
My next trick will be to run well beyond the zero on the very conservative “Distance to Empty” reading to see if I can join the 600 mile club (965.4km) on one tank. Considering that the tank is 45l but the most I’ve squeezed in is 38.02l, that should be easy with another 7 untapped litres! But I’ll take 5 litres spare just in case.