Mazda engine news almost trumps these delightful diesels

The Mazda6 Limited diesel wagon - our choice of the two, but its not an SUV.
Rob Maetzig/Stuff

The Mazda6 Limited diesel wagon - our choice of the two, but its not an SUV.

Wouldn't you know it? The moment you start writing an article about a couple of really good Mazda diesel vehicles, news comes out that sort of gazumps the point of it all.

Well, not really. But word that Mazda boffins have developed a new petrol engine that operates not by the traditional spark ignition, but by the compression ignition method that up until now has always been the preserve of diesel engines, really does introduce an important question: Do diesel engines have a future in passenger vehicles?

Diesel-powered passenger vehicles are great. Although they are traditionally more expensive to buy, they can quickly redeem themselves via their superior fuel economy and the torquey drive they offer. And although in the past they were also noisier than petrol equivalents, these days that's pretty well been sorted out to the extent a diesel engine note is now more of a relaxing hum than a rattle. 

The Mazda CX-5 Limited diesel SUV - its major advantage is that it is an SUV.
Rob Maetzig/Stuff

The Mazda CX-5 Limited diesel SUV - its major advantage is that it is an SUV.

It could be said that the only remaining hassle with diesel is that the owner of such a vehicle has to pay the dreaded Road User Charge of $62 per 1000km to earn the right to drive it on our roads. But then again owners of petrol-engined passenger vehicles pay an excise tax of 59.524 cents per litre whenever they buy their fuel - its just that they pay that tax at the pump, while the diesel RUCs have to be purchased elsewhere.

READ MORE: Revolutionary new Mazda petrol engine

 
Mazda6 had a recent minor facelift, and is a good-looking wagon.
Rob Maetzig/Stuff

Mazda6 had a recent minor facelift, and is a good-looking wagon.

One of the outstanding examples of the progress being achieved with diesel engines is the Mazda SkyActiv-D.

It features the world's lowest compression ratio of 14 to 1, which improves combustion timing which in turn results in much cleaner emissions and a low average fuel consumption. It also uses a two-stage turbocharger - one small and one bigger - which operate individually or together according to driving conditions.

When this engine was first introduced by Mazda a few ago as part of a series of SkyActiv environmental, safety and performance technologies, it immediately won fans for its excellence. The SkyActiv-D powertrain continues to impress - and it is under the bonnet of a pair of notable Mazdas that are the subject of this review - the Mazda6 Limited wagon, and the CX-5 Limited SUV.

Mazda CX-5 is so good it is a strong contender for this year's New Zealand Car of the Year honours.
Rob Maetzig/Stuff

Mazda CX-5 is so good it is a strong contender for this year's New Zealand Car of the Year honours.

We chose to do this twin test because in many respects these two vehicles are closely related. They're built on the same platform, are powered by the same 2.2-litre SkyActiv-D engine, offer the same Limited level of specification, and offer the same rear-tailgate practicality - it's just that one is an old-school wagon while the other is a new-age SUV.

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They've both been been updated in recent times, too.

With the Mazda6 there's been a bit of a cosmetic touch-up via such things as a new exterior mirror design, new steering wheel and revised instrument panel, and at the Limited level the model has also received heated rear seats and a full-colour heads-up display.

Mazda6 interior includes a colour heads-up display.
Rob Maetzig/Stuff

Mazda6 interior includes a colour heads-up display.

A variety of active driving assistance technologies have been added to the car, including an improved radar cruise control system, and pedestrian recognition in a low-speed collision mitigation system called Smart City Brake Support. This model also now has Mazda's very good G-Vectoring Control, which automatically smooths out steering and reduces body roll during cornering by reducing engine torque.

The CX-5 has undergone big change, with 698 new parts allowing Mazda to claim the vehicle is a new-generation model even though the powertrain remains essentially the same. It's an outstanding SUV, featuring a much sharper external design and a considerably improved interior. In terms of standard specification it's got everything the Mazda6 wagon has, with the one major difference at the Limited level being all-wheel drive, which obviously is a prerequisite for a proper SUV.

This CX-5 is so good it is strongly in line to be selected as this year's New Zealand Car of the Year. And yet, right at the top of the CX-5 selection I don't think the Limited diesel is as good as its Mazda6 equivalent.

The lovely interior of the Mazda CX-5 Limited.
Rob Maetzig/stuff

The lovely interior of the Mazda CX-5 Limited.

From the point of view of practicality, the wagon is longer and has more interior room than the SUV, particularly when it comes to rear storage. The wagon offers 506 litres of cargo room with all seats in use, growing to 1645 litres when the rear seats are folded down; while the CX-5's cargo room with all seats in use is 455 litres, growing to 1355 litres when the rear seats are folded down.

While both vehicles are powered by the same engine that generates 129kW of power at 4500rpm and 420Nm of torque at 2000rpm, it is the Mazda6 that performs the better, simply because it is lighter - its kerb weight is 1607kg while the CX-5 is 1729kg. Consequently, official average fuel consumption is superior at 5.4 L/100km while the CX-5's is 6.0 L/100km. And of course emissions are less.

However, the Mazda6 Limited wagon has one thing against it - it is a traditional wagon and the CX-5 is an SUV, and these days everyone wants SUVs. 

But what is the future for both of these vehicles? Will the arrival from 2018 of Mazda's flash new SkyActiv-X compression-ignition petrol engine spell the end of the marque's remaining diesels - after all, Mazda New Zealand has already discontinued diesel options for the Mazda3 and the CX-3, leaving only the Mazda6 and the CX-5 to offer diesel. Between them they take 8.7 per cent of all Mazda passenger sales, and that's not much.

The entire New Zealand new vehicle industry is experiencing a steady fall in diesel sales, and Mazda reckons this is due to significant gains in the efficiency of new-generation petrol engines such as the brand's current SkyActiv-G offerings and, soon, SkyActiv-X.

Glenn Harris, Mazda New Zealand's general manager of sales and marketing, was asked whether he thought the company will ever drop diesels from the passenger lineup.

"It's reasonable to expect that each new technology release is better than those that have been in market for some time," he said.

"SkyActiv-X will complement our existing SkyActiv-G/D engines for some time, but in the interests of reducing complexity and to maximise the opportunity of a technology that offers the best of both petrol and diesel engines but without the pitfalls of each, my expectation is that the SkyActiv-X engine will be our engine of choice over time."

So there you go. Maybe Harris is signalling that even though diesel will be around for a while yet (and we understand an improved SkyActiv-D engine is under development), it may be a case of X marking the spot for the longer-term future. Meanwhile, we're enjoying where the brand is at now with its diesel technology.

 - Stuff

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