1132.5km on 45.17L – But is it enough?

1132.5km at 44km/h.  A shame that the 3.7 l/100km figure is so unreliable.
1132.5km at 44km/h. A shame that the 3.7 l/100km figure is so unreliable.

I should be very happy.

  • I’ve just registered my best fuel consumption result of 3.99L/100km.  That’s 70.8 mpg Imp, 58.9 mpg US and 25.06 km/L.
  • First dot lasted 177 km
  • Fuel warning beep at 903.3 km
  • DTE = 0 at c. 960 km, driving another 170 km.
  • My last 553.7 km was at 3.5 L/100km (3.7 corrected 63.5 mpg US) and 45 km/h

I’m sad because I was aiming to drive 700 miles (1126.5 km) on a single 45 L tank and I’m not sure if I made it within any margin of error.

The Priuschat 600-, 700- and 800-miles clubs

The Priuschat forums include the above-mentioned clubs for reaching the equivalent of 965.6 km, 1126.5 km and 1287.4 km on a single tank of fuel.  To anyone new to the Prius, the thought of driving so far on a tiny 45L tank seems impossible.  To put things into perspective, if my old Citroën drove at 3.99L/100km its 66L tank could have driven 1650 km or over 1000 miles.

I’ve had 3 tanks in the 600 mile range, 2 of which were over 1000 km.  But my best tanks have never cracked the 4.0L/100km mark.

So when I started with 3.7L/100km on the HSI display and maintained it, I thought that I could reach 1126 km with a tiny margin for error, about 24 km to be precise.  I say “precise”, however the Distance to Empty (DTE) reading is so conservative and the HSI so optimistic that I use a spreadsheet to calculate the theoretical distance.  There’s a big difference between 1150km and 1126km if you get it wrong.

So to make things safe, I added fuel from a jerry can I had in the garage.  Over 12 months ago it was about 5 litres of 95 RON.  What it had degraded to in that time was unknown, but it probably would not have been well-received in my Citroën but should be at least 91 RON and good enough for the Prius.

I found an oil resistant measuring jug to accurately add 4600ml to the tank yesterday, good for about 130 km.  I was banking on filling the tank with 40 litres or less to make it certain.  But that’s where the uncertainty creeps in.

Did I make it?

Had I exceeded the mark comfortably, the result would not be in question.  But because it looks like I scraped it in I’m duty-bound to explain and to grovel.

The jerry can contained 4.6L of fuel.  After reaching 1132.5km, I filled to the first click of the nozzle.  The volume registered was 40.57L.  That gives a total of 45.17L.  Can you fit 45.17L into the “45 litre” tank?

Certainly, it is possible to squeeze more into a tank.  The hardcore Japanese Prius maniacs jack up the rear wheel to fit more into the tank.  Too much of this will soak the anti-vapour carbon canister, but if you are just about to drive a long distance, it won’t stay soaked for long.

But can there be more than 45L put into the tank using standard fuelling techniques and not going past the first click?

So confident, I was…

The HSI display showed 3.7L/100km for almost the entire tank.  Many trips were recorded at 3.0 – 3.9 LHK on my Scangauge-e and Garmin ecorouteHD, which are more accurate than the HSI.  I had to be below the consumption curve to reach 1126.  Surely.

However, I was adding 5.8% to the HSI figure of 3.7 to get 3.91.  But what if the HSI was 3.75 instead of 3.70 (assuming that 3.76 is rounded to 3.8)?  Then the true figure goes from 3.9 to 4.0.  At 4.oL/100km a 45L tank goes just 1125km, 1.5km short.

My Scangauge calibration could not calculate Distance to Empty accurately, which could have been useful.

New benchmark

My first sub-4L/100km tank and first time over 1100km.

At least I know that 1100km is attainable with moderate effort.  I hypermiled, pre-warmed the engine, kept the battery topped-up and used A/C sparingly.  My wife didn’t drive because  she was in Japan for 2 weeks (she thinks the P&G is a company that makes shampoo) so there were no full-throttle take-offs or hard braking.  (She’s not a bad driver, just not a hypermiler.  She used to drive 50,000km per year for 3 years in a previous job, so she’s very capable.)

It also tells me that unless I see a HSI figure of 3.5 or 3.6, 1126.5km is not going to happen.

You don’t want to join a club by tripping over the threshold, you want to stride in there with confidence.  If I miss out this time, I’ll put in another bid later.

Read more: http://priuschat.com/threads/700-mile-club.112286/page-8#ixzz2LHfwAKPi


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