2012 Mazda Mazda3: Cold Starts
June 14, 2012
The Skyactiv-ness of our longterm 2012 Mazda 3 is the real deal, as we've confirmed in our recent fuel economy test of 40-mpg cars. We used a 3 sedan for that test, by the way.
Somewhat related: one thing I've noticed about the Skyactiv engine in our longterm car is a muted high frequency 'shh' noise (it's not exactly a ticking, more like the sound made by tiny pebbles placed on the exhaust heatshield of an idling engine) during cold starts. Some owners might mistake the source as being from the engine's direct injectors.
Turns out the exhaust manifold has thin walls and thus transmits more combustion noise than if it was some old-school cast iron chunkus. When cold, the ignition timing is retarded which puts more heat into the catalyst to aid light-off. This retarded timing also has stronger exhaust blowdown pulses, and that's what you're hearing.
The sound is hardly annoying, but it's there. And it's normal.
Jason Kavanagh, Engineering Editor