Maximising Fuel Consumption

Maximising Fuel Consumption

Driving a six cylinder car does not have to be a costly exercise in these days of high fuel prices. A pair of Nissan Maximas powered by 3.5 litre V6 engines with four speed automatic transmissions recently averaged well under 9 litres per 100 kilometres - over 32 miles per gallon - on a 430 km route from Auckland through the Waikato and around the Coromandel Peninsula.

The cars, both in Ti specification, were driven by the New Zealand Automobile Association’s Technical Advice Manager Jack Biddle and Motoring Advisor Steve Vermeulen at normal road speeds. One car used Mobil's Synergy 8000 petrol, which has a minimum octane rating of 97.5, while the other ran on 91 octane, Synergy 1000.

To replicate real world driving conditions, both cars carried an adult passenger and 35 kgs of ballast in the boot to represent a modest load of luggage.

Before the drive started from Manukau City both car's tyres were pressured to the lower of Nissan's two recommended pressures, 35 psi in the front and 32 psi at the rear. On a warm spring day, the four occupants voted unanimously to use the air conditioning, which does use extra fuel. No competitive economy rally techniques were employed, such as switching off the air conditioning, running ultra high tyre pressures or coasting down hills in neutral gear. Both cars were fuelled up and then refuelled at the end of the journey at exactly the same fuel pumps.

After 432.5 kms the Maxima running on Synergy 8000 had managed 8.46 litres per 100 kilometres or 33.3 miles per gallon. The car running on 91 octane used 8.78 litres for every 100 kilometres travelled or 32.1 miles per gallon.

From Manukau City the route headed south on the motorway and then across the notorious Highway 2 through Maramarua and across the Hauraki Plains to Paeroa and a morning tea stop at Waihi.

At Paeroa at the end of the easiest driving of the whole trip, both cars on board computers were showing they were sipping fuel at a very frugal 8 litres per 100 kilometres.

The final calculated consumption figures revealed the on board computer was accurate to the nearest tenth of a litre.

After leaving Waihi and negotiating the first of several winding and twisty hill climbs around the Coromandel Peninsula, the consumption had reached 8.4 litres per 100 kilometres at Whangamata and 8.6 at Tairua. The Kuaotunu hill sent the onboard computer up to 8.7 and by the time the Whangapoua hill had been crested the consumption was 8.9 litres per 100 kilometres.

Accelerating out of the tight bends while climbing the hills and then slowing for the next corner did not engender economical driving, but it was real world conditions. After Coromandel there are two more major climbs before reaching the pretty coast line drive back down the Firth of Thames. The net result was the worst figure of the trip - 9.0 litres per 100 kilometres.

By Thames it was back down to 8.9, while the Hauraki Plains were recrossed and the consumption dropped to 8.8 on reaching Mangatawhiri. Then it was back onto the motorway at Pokeno and the consumption dropped to 8.7 litres per 100 kilometres just before reaching Manukau City.

When the fuel tanks were topped up the Synergy 8000 fuelled Maxima needed 36.54 litres at $1.60.9 a litre for a total of $58.79, while the 91 octane car used 38.03 litres at $1.51.9 costing $57.77. Apart from the motorway travel, only one vehicle passed the two Maximas during the day as both cars were driven at normal open road cruising speeds with the traffic flow.

The results surprised everybody involved; demonstrating a six cylinder car with two adults and 35 kgs of luggage and a flexibly powerful 170 kWs motor can achieve good fuel economy when driven sensibly.

Both Biddle and Vermeulen made particular comment of the advantages of the sophisticated on-board computer engine management system in the Maxima, adapting to the lower grade 91 octane and still producing economy figures close to the car running on Synergy 8000.

Mr Biddle commended Nissan New Zealand Limited for taking the initiative to arrange this fuel test. The New Zealand Automobile Association was delighted to be involved and to act to ensure the independence of the test.

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