The Toyota Prado owner’s manual states that my 2005 Prado GXL 120 series with the 4.0 L petrol engine (1GR-FE engine) should be run on unleaded petrol (gasoline) with a RON of 91 or higher. For improved vehicle performance they recommend using fuel with a RON of 95 or higher. But what difference does this actually make in the real world? And does the increased efficiency of premium fuel offset its higher price?

I bought my Toyota Prado second hand in December 2010 with 101,000 km on the clock. Two weeks after purchasing the Prado I set off for Tasmania (from Queensland). 6,700 km and 23 days later I returned to Brisbane. My Prado is now being used for general around town driving, as well as the occasional highway trip. We are setting the car up for some beach and bush camping in the near future.

My understanding (based on internet research) is that the Prado has an engine management system that takes several thousand kilometres to adapt to higher octane fuel. With dual tanks and a total fuel capacity of 180 L, the Prado can travel a considerable distance between fuel stops. With the best fuel economy figures I have achieved, 1,600 km is theoretically possible on one tank (including the subtank)!

I started tracking my fuel consumption at the beginning of my trip to Tasmania. There are many variables that influence fuel consumption. The fuel octane is obviously one consideration. But things like tyre pressures, cargo load, passengers, type of driving and accessories fitted all influence fuel consumption. Highway driving with the cruise control on all day will give very different results to sitting in heavy traffic.

The linked Prado fuel economy spreadsheet shows my fuel economy figures as well as notes on usage and other variables. Note that the fuel used on a particular date correlates with the fuel economy achieved and recorded during the following re-fuel. Unfortunately, I have misplaced my records for the first two tanks of fuel running on E10.

Fuel I have used includes:

Shell PULP (V-Power RON 98 octane) and E10 (minimum RON 94 octane)
BP  Ultimate (RON 98 octane) and PULP (RON 95 octane)
7 – Eleven PULP and E10 (web site does not show information about their fuels)

My records indicate a best fuel economy figure of 11.12 L/100 km and a worst figure of 17.08 L/100 km running on premium unleaded (RON 98 octane). The worst figure I would consider an aberration because it involved a lot of sitting in the car in 36 degree heat with the engine and air conditioning running while waiting for school pick-ups and making business phone calls. I would normally turn my engine off during these periods.

I plan to refuel using E10 a couple of times to get a comparable fuel economy figure for the lower octane fuel. I will then be able to make a comparison to compare whether it is worth spending the extra money for the higher octane fuel.

Update: more than 26,000 kilometres of driving and 3,800 litres of fuel, and I have a result — read here.