Just to correct the speculation as to whether the 2.5litre normally aspirated engine is completely new, and what constitutes a brand new engine, lets try to be clear about what is new and what is not, so you can decide for yourself.
The updated Mazda6 introduced at the Los Angeles Auto Show this past week offers two powertrain options in the US: an upgraded SKYACTIV-G 2.5 naturally aspirated engine and the turbocharged SKYACTIV-G 2.5T engine, first unveiled at the 2015 LA Auto Show for the 2016 CX-9.
For 2016 (in the Japanese, US and AUS markets) Mazda6’s 2.5-liter, four-cylinder engine that first appeared in 2013 comes with a number of upgrades:
1) Employing the tried and tested piston dampening technology that aim to reduce internal friction and improve efficiency across all rpm, and also adds a greater level of refinement.
2) A new technology that is unique to Mazda in North America is cylinder deactivation in a four-cylinder engine. The outside two cylinders can shut down when the vehicle is operated at steady speeds between 25 and 50 mph, where valves are controlled by a switch in the hydraulic lash adjusters that in turn stop the valves from moving. All four cylinders work instantaneously when needed for maximum performance. A centrifugal pendulum has been adopted in the torque converter of the six-speed SKYACTIV-DRIVE automatic transmission, counterbalancing any vibration that might otherwise be felt when running on two cylinders. The result is an imperceptible switchover between two- and four-cylinder modes.
So for the normally aspirated engine that you're interested in, in my view as an engineer, the engine is fundamentally the same, but the control systems are doing something smart in order to improve fuel economy.
For those who are exceedingly sceptical, these engines are now publicly tried and tested. Given there's no signs of issues or problems in the two years that they've been on sale, I would say they are pretty robust, but that's not surprising considering the engine block is in its current iteration unchanged for several years.
There seems to be a perception from some quarters that car manufacturers don't do enough to test their engines, but believe me having been on the front line, all mainstream manufacturers undergo stress testing beyond abnormal operating conditions
Just to make yet another point regarding the Mk2 GH series 2.2 diesel timing chain....whilst Mazda may not publicly admit it, they were too busy working on the future Skyactiv-D and G range of engines, to focus enough time on making a decent timing chain and tensioner combo for their MZR 2.2 diesel, which was a slightly rushed job as they wanted to develop an engine to meet the Euro 5 emissions standards in 2008. They did not address the chain issue as the GH model was only intended to be around until 2012/13.
Allegedly the model most likely to be affected was he short-lived 185bhp 2.2 MZR diesel (which is the car I have), and the 2010 - 2012 180bhp 2.2 diesel was not afflicted in the same way. Unfortunately for Mazda, this problem has stuck with them and is repeatedly discussed (often with lots of misinterpretation/misunderstanding) so that all of a sudden, their product is deemed risky.
I've just replaced my timing chain at 151,000 miles, and I'm monitoring the timing chain stretch on a weekly basis so I can better predict the rate of stretch. This issue would not stop me buying the latest generation of Mazda 6.
I've seen it first hand and test driven it already. It's a great car in terms of build quality and finish and I would say it is comparable to a BMW, Audi or Mercedes. Again, I speak with first hand experience of working in the de-fleet and re-marketing industry. I've seen tens of thousands of these premium segment cars between the age of 6months to 4years, and so many of them rattle and the interiors don't wear so well in comparison with my 2009 sport luxury model.
The new 6 is noticeably quieter than the outgoing model thanks to acoustic glass and better use of sound dampening materials, and is as quiet as an Audi A4, which is quieter than a Merc C class and BMW 3 or 4 series.
The driving position and handling is great, and the standard features are much higher than its competitors, with the excellent HUD, city brake, RVM, front and rear safety braking, adaptive cruise control and g-vectoring available on all models. Mazda also don't have a habit of over-exaggerating their fuel economy figures, where some of other German, Japanese and British marques seem to be 20% - 35% off their figures.
When the time is right, I'll be driving the 2.5litre tourer if I don't import a CX8 or CX9 from Australia.