Over the past several years, we've noticed the trend across a wide range of vehicles. Such is the case, too, with the latest versions of the Mazda3 introduced last year, and with the new 2012 Mazda5 we drove this past week.
And it actually has nothing to do with cost-cutting, or with lean instrument-panel design (although we do like the new hooded gauge clusters in Mazda's latest vehicles, with their large round dials).
According to Robert Davis, Mazda's senior vice president for quality, research and development, there's a cool blue 'cold' light instead of a temperature gauge because of consumer psychology: In short, owners are more likely to drive gently—and “not thrash the engine”—if there's a light on than if the temp gauge simply shows cold.
There's a lot of misinformation in question-and-answer sites about revving an engine when cold. For the truth here, look at nearly any vehicle owner's manual; most advise against revving an engine too high when cold, for good reason. The alloy parts of an engine don't fit together in quite the same way until fully warm, and the oil pump has to work especially hard to get oil into the smallest spaces when the oil is thicker.
And with the thinner oils being introduced this year and over the next several model years—allowing better fuel economy and good high-heat protection—they counterintuitively place engines under higher stress in cold starts.
For 2011, Mazda is transitioning to zero-weight (0W20) synthetic motor oil in all of its four-cylinder engines, which enables an extended service interval of 10,000 miles in light-duty use (easy highway driving) or 7,500 miles in normal use (more stop-and-go, shorter trips).
Some might be disappointed to see these gauges go away, as slight variations in coolant temperature are often your first sign that thermostats are sluggish or radiator passages are becoming clogged or corroded.
But based on several follow-up questions with other automakers' engineers, temperature gauges aren't going away completely; we'll continue to see them in performance vehicles, as well as in vehicles that are often modified in the aftermarket.