What's that Button do?

"Eco" buttons are common features in many of today’s new cars, but what exactly do they do?

Manufacturers aren’t specific as to whether eco is short for “economy” or “ecology,” and when pressed on the issue, one manufacturer’s representative said the button stood for both. Some automakers have removed all doubt by labeling the button “Econ.”

Regardless, pressing the "Eco" or "Econ" button on your new car could alter throttle response, decrease the air conditioning and change transmission shift points. Here’s how each of these work.

In cars such as the Dodge Caravan, Honda Insight, Honda CR-Z and Infiniti M, plus Toyota and Lexus hybrids, Eco mode smoothes throttle responses. This allows the vehicle to overcome a driver who taps his toes in response to a favorite tune, or makes rapid and abrupt throttle movements.  However, with Eco mode on, pressing half way down on the accelerator pedal might only give you 30 or 40 percent of the available power.

One thing these systems usually have in common is the ability to get maximum power when flooring the throttle. Drivers don’t have to switch out of Eco mode to avoid a large tractor-trailer rig barreling down the highway. 

Shift patterns also change in Eco mode. Expect the automatic transmission to shift to a higher gear sooner, delay downshifting when you want mid-range acceleration, and stay in a higher gear longer as you slow down. All of these actions boost fuel economy. Some vehicles also reduce slippage in the transmission by going into “lockup mode” sooner and staying in it longer.

Air conditioning uses gasoline. The added drag of the air conditioning compressor on the engine can drop fuel economy by a mile or two per gallon. Actively managing the use of air conditioning will save some fuel and most drivers will notice little difference in comfort.

Some people have suggested that using the air conditioning on the highway rather than opening the windows is a wash, since open windows produce more air turbulence and drag, which is overcome by burning more gasoline. At lower speeds, however, where aerodynamics plays a lesser role in fuel economy, open windows are the clear fuel economy winner.  Individuals seeking top fuel economy, otherwise known as “hyper milers,” keep their windows closed and air conditioning off regardless.

Searching for government figures on the effectiveness of Eco mode is fruitless, as EPA testing is done in normal mode. However, manufacturers do claim a five-to-10 percent improvement for many “typical” drivers.

 

Older readers probably remember the Mobil Economy Runs, which took place annually from 1936 to 1968, minus the World War II years.  Here, drivers competed for their automaker employers using every trick they could to muster the best fuel economy.

One driver who competed successfully for Chrysler in the mid-60s told me years later that he drove with a very light touch on the throttle, did everything possible to cajole the automatic transmission to shift to a higher gear sooner – and then stay there – and never opened the windows or used any electrical accessory unless absolutely necessary. He obviously did not need an eco button.  However, for the rest of us…

 

<i>Jim MacPherson is the host of "The Car Doctor" show airing Sundays at noon on WTIC-AM. Paula MacPherson is his wife and new-car review partner. Send comments, questions, suggestions in care of Special Publications, Hartford Courant, 285 Broad St., Hartford, CT 06115, or email jdee@courant.com.</i>

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