Mazda Mazda6 2014 Review

Gut feeling suggests i-stop does save a significant quantity of fuel, but finding a way of testing the system in a sequence of accurate iterations is not as easy as it sounds.

So here's my unscientific take for you to accept or discard...

Two runs from Melbourne's outer western suburbs to the Dandenongs in the east, with a loop through the CBD were rendered impeachable because one night the traffic was slow and heavy as the night-club set called on the full resources of the city's taxi fleet. That was the night I drove the Mazda6 along the set route with the i-stop system enabled.

Another night the traffic was practically non-existent. And that was the night I tested the car for economy with i-stop disabled. On both occasions the run ended with the trip computer posting an average figure of 6.2L/100km.

I chose to monitor the trip computer readout because it's more accurate than filling the tank to two clicks and manually calculating the rate of consumption. Also, it provided me the means of monitoring fuel consumption on the move, to see where and when the Mazda was more (or less) economical.

Temperatures were mild (below 20 degrees on both nights, but above 11 degrees) and the weather was fine and calm -- no cross winds or rain. I turned off the ECO mode for the climate control system and reset the trip computer each time, naturally. On the open road (where i-stop played no part at all), the Mazda6 was achieving an average of 6.0L/100km, adhering to the respective 80/100/110km/h speed limits over a 15km section. But the trip computer indicates the Mazda can be more economical still at speeds of around 80km/h, where aerodynamic drag won't bite as badly.

On the quieter night, with the i-stop disabled and the engine running continuously, the Mazda had halted 27 times for traffic lights between Melton and the intersection of Grange Road and Toorak Road in Toorak. During the 'Saturday Night Fever' test, i-stop had killed the engine 41 times over the same distance -- a 50 per cent higher frequency. Total time with the engine switched off automatically by i-stop was around 28 minutes for 58 stops in total -- just under a 30-second average.

Clearly the Saturday night run was more taxing, yet by the time the car was 6km away from Lilydale (having travelled 100km exactly), the fuel consumption figures were 6.3L/100km with i-stop enabled, 6.4 with i-stop disabled. So without even making allowances for the heavier traffic and the higher frequency of stop/start operation, i-stop had saved 0.1 litres over a hundred km section of road. That would add up to about 20 litres of fuel for every 20,000km travelled.

For the two runs acceleration was kept to the optimal rate. The engine never revved above 3000rpm, but credit to the Mazda, nor did it need to in traffic. Acceleration was fine, even driven gently. The performance was enough to stay with the traffic up to the 60km/h limit (or lower where that applied), and the Mazda's torque could be relied on to build up speed progressively in higher gears (say between 60km/h and the speed limit in 80km/h zones), without detracting from the car's driveability. At speeds above 80km/h (in 100/110km/h zones), I was adjusting speed with the cruise control.

Tellingly, on the run into the city, through Melbourne's western suburbs, the car posted a fuel consumption figure as low as 5.5L/100km with the i-stop system operating. On the Sunday night, without the i-stop system enabled, the fuel consumption figure never fell below 6.0L/100km. Based on that leg -- an approximate distance of 40km, including 15km on the open road -- that half a litre would translate to 100 litres saved for 20,000km travelled.

So right up to Flemington Road, the i-stop system was proving itself an invaluable adjunct to the total fuel saving package -- and then the nightclubbers arrived on the scene... at 10pm. Damned clubbers.

Dissatisfied with my first attempt at testing the car's fuel economy, I tried again using a different route and a revised format that we've tried in the past. By running eight 'laps' of an urban circuit comprising freeway, arterial road and inner urban tram routes, each lap alternating between i-stop on and i-stop off, I hoped to establish a series of datapoints that would average out discrepancies due to traffic, weather and other factors.

Nice idea perhaps, but the mice were sent into a panic-struck frenzy as my carefully crafted plan came unglued. First, a cool change during the second lap sent the temperature plummeting 10 degrees in a matter of minutes. Plus, it seemed like every new lap with the i-stop enabled involved following a tram up Bridge Road in Richmond, whereas traffic was comparatively light every time I ran the same gauntlet with the i-stop disabled.

For the record, averaging the laps resulted in fuel consumption figures of 7.35L/100km in both modes. That's about what our experience has been over the 4500km duration since we picked up the car from Mazda. Rarely has the trip computer posted a figure above 8.0L/100km, even when confined to driving around city and suburbs. Most of the time it has hovered around 7.5 or 7.6L/100km.

As for the benefit of i-stop, I'm none the wiser, despite spending a day and a half driving a Mazda6 for optimal economy. And if you think I'm going to give it another try after all that, you're as crazy as I am.

2014 Mazda Mazda6 Touring pricing and specifications:
Price: $37.500 (plus on-road costs)
Engine: 2.5-litre four-cylinder petrol
Output: 138kW/250Nm
Transmission: Six-speed automatic
Fuel: 6.6L/100km (combined)
CO2: 153g/km (combined)
Safety Rating: Five-star ANCAP

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