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Chevrolet Volt tricks: Using Mountain mode to preserve range

Consumer Reports News: December 23, 2011 09:53 AM

If you commute to the city, why drive a plug-in hybrid only to burn down all your range upfront on the highway? To do so, means slogging through the city on gasoline once the batteries run flat, rather than use the more efficient, quieter, zero-emissions electricity to motor around the urban environment.

The solution is known as a “Preserve Mode,” triggered by a button on the dashboard that allows the driver to override the hybrid system and run on gas power on the highway to preserve the batteries’ charge.

The upcoming plug-in version of the Toyota Prius is the only hybrid that has an actual Preserve Mode. Chevrolet Volts destined for export markets have it. American Volt fans, however, have found it disguised as something else...

The Volt has what General Motors calls Mountain mode, along with Normal and Sport. Mountain mode was designed for climbing three of the longest mountain grades in the United States. It cuts about 10 miles off the normal electric range of the Volt to expand the battery’s “buffer” zone— the 20-25 percent of charge that’s left after the car switches to gas mode. By engaging Mountain Mode when you take off, you can save those last 10 miles for later use, even if there are no mountains in sight. When you want to go back into electric mode later, you just select Normal; the battery buffer shrinks back to its normal size, and the engine switches off, giving you another 10 miles of petroleum-free driving.

Wanting to show off the car to my family on EV mode one night, I was frustrated that my normal 40-mile commute would completely deplete the battery’s projected 38-mile range—until I remembered Mountain mode. I tried it and learned it works fine, even on comparatively level ground. And, my family was impressed gliding silently around in the Volt on electric power.

After three more days of experimenting, I found it was easy to control when the gas engine came on during the commute. I could strategically set aside 10 miles of battery range for use on back roads, rather than burn it up at highway-speed.

So why did GM choose not to feature Preserve mode on domestically sold Volts? Because for emission purposes as spelled out by the EPA, the electric drive cycle must be used first. The EPA’s mandate is to prioritize air (and water) quality, not energy efficiency. So from that perspective, it makes sense for the EPA to ensure plug-in hybrids use all their clean battery power with every drive, before emitting any air pollution by starting the engine.

In my experimenting, I found I couldn’t always figure out exactly when to re-engage Normal drive mode to make sure I used all the batteries with every drive. Clearly there’s a learning curve, and I’m sure I would eventually have figured it out for my daily drive. (And yes, I know electric power plants also generate air pollution. That’s a separate discussion.)

The availability of Mountain mode—even when you’re not in the mountains - gives a tantalizing glimpse of the possibilities for maximizing efficiency when you’ve got both a gas engine and batteries. I can’t wait to try out the Preserve mode in the plug-in Prius.

Eric Evarts

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