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Discussion Starter · #1 ·
I just completed some controlled highway fuel mileage testing with my 2013 Volt. In very careful testing removing all possible variables, I found that I get about 38.5 mpg at 60 mph, 35.5 at 67mph and 34 at 73mph. Once I had that figured out, I topped off, reset the trip meter and engaged MM at 60 mph. Having never used it before, I was surprised to see it go from a flat battery to 1/2 charge in 13.3 miles using .65 gallons of gas.

Knowing that I get 38.5 mpg at 60, I would have used .345 of a gallon to go 13.3 miles but since it used .65 gal because of Mountain Mode, it took an extra .30 gal just for that function..... I also learned that it stops when it's at half charge.

But from there I got confused. I thought that MM would leave me with some useable battery but that's not the case. While the MM battery (gray in color) showed it was at half, I found that it cannot be accessed in any other way. I could not go back to normal driving mode as the battery was still considered flat. So, I thought maybe if I shut the car off and back on, it will show usable battery that had come from the MM charge. That didn't work either. So I thought maybe it would show up when I plugged in the charger but it still took the full recharge cycle that comes with a flat battery. Is the charge from MM ever accessible for use other than when a hill is encountered? Is it only usable in MM?

Please help me understand. I'm driving on a 900 mile trip in somewhat hilly terrain, I leave tomorrow. If I go to Hold mode while I still have some battery remaining, will it take what it needs to go up the hills efficiently? Or does it need to be in Mountain Mode for that? Which way will give me the best overall MPG?
 

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You won't be able to see the difference in MPG between the two.

Mountain mode is leaving you usable battery power - if you switch back to normal mode, the engine won't run for 12-14 miles until the battery is back down to the normal CS range. However, the car knows that the energy in the battery came from the ICE, and so the car accounts those miles as "gas" miles on the usage displays. In 2011/2012 Volts, turning the car off and back on would reset the accounting - I didn't know they'd changed that. Either way, it's just accounting on the energy usage screen, it doesn't change the way the car is actually operating.

If you go into Hold mode as soon as you hit the freeway, you'll accomplish everything that Mountain mode is designed to do. Mountain mode just retains (or rebuilds, if needed) ~3.5 kWh of usable battery to allow the car to exceed the engine's output for several minutes while charging up mountains at high freeway speed (there are only a few roads in the US which really benefit from Mountain mode, mostly in the Rockies and the Sierra Nevadas.) As long as you're in Hold mode with more than 3.5 kWh usable in the battery, you won't gain anything useful from switching to Mountain Mode (2011 and 2012 Volts don't have Hold mode.)

Your average drive in hilly terrain won't drain the standard 1 kWh buffer even if you're driving aggressively. If you start seeing "Propulsion Power Reduced" messages while the engine is running at high RPM, you'll know that the terrain you're in is severe enough under your current driving pattern to benefit from Mountain or Hold. Even then, it's not a catastrophe; the worst case is you have to limp up the hill at a lower speed than you'd planned - likely still faster than Semis can manage.
 

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To answer your last question of MM or Hold, which gets the best MPG, it really does not matter, the net result will be the same (all other variables being constant). Hold mode keep your battery about where it was when you went to hold mode. It uses some battery to go up hill, then the ICE recharges this small amount used when there is less demand for power. MM is just a variation of this. The intent of MM is to turn it on while you still have lots of battery. The Volt will then reserve about half the battery for the more demanding mountain drive, like climbing Pikes Peak. Like hold mode, MM will replace the energy used from the ICE generation when there is less demand for power, such as on a down hill.

In your scenario you first drained the battery below half so when you went to MM the ICE had to work extra hard to replace the used battery energy and get it back to about half. Yes you can access this battery energy. Just switch back to Normal Mode and the ICE will shut down and you will be running on battery, until it is drained. However, since the ICE had to charge the battery, the miles you drive using this battery energy will be credited to you gasoline miles.
 

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Mountain mode changes the "low battery" point where the engine will run. If you are above about 15 miles of range when you engage it nothing will happen until you get to 15 miles. At that point the engine starts to hold it there.

Conversely, if you are below 15 miles range when you engage MM, it will run the engine to power the car PLUS charge the battery back up to about 15 miles of range then hold it there.

Hold mode will hold the battery state of charge where it is.

When you were at 1/2 charge you should have been able to go back to Normal and use that battery power. I you sure you didn't put it in Hold mode? Just realize that that charge generated by the engine from gas costs you about 3X what it costs to charge from the wall. You only want to engage MM below 1/2 charge when you KNOW you NEED it for upcoming terrain and you didn't engage it earlier.

MM is desired when you are going to climb a hill that is steep and long enough that you would run out of battery and ONLY have engine power "Reduced Propulsion". We're talking serious grades like I5 between LA and Vegas. I'm not sure if there is anything east of the Mississippi beside Mt. Washington that NEEDS MM.

For your trip, in most cases you would want to just run in normal mode. If you have around town miles you may want to use Hold to save battery for them for convenience of not having the engine running when you are driving around town. Just make sure you don't arrive at a charger with range in the battery because you wasted cheap electricity while using expensive electricity from gas.

Have a great trip in your Volt!
 

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Discussion Starter · #5 ·
See, that's where I got confused. I could not switch back to normal mode. I had completely drained the battery, went to mountain mode and built up a half charge, but I could not switch back to normal. It was not an option on the drive mode display, it was dark. Even after I turned the car off and back on, I couldn't switch back to normal.
 

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See, that's where I got confused. I could not switch back to normal mode. I had completely drained the battery, went to mountain mode and built up a half charge, but I could not switch back to normal. It was not an option on the drive mode display, it was dark. Even after I turned the car off and back on, I couldn't switch back to normal.
I've never seen or heard of that before. Might be a glitch? You certainly should be able to switch from Mountain Mode back to Normal Mode during regular driving. If you can repeat the events, maybe take a video?
 

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Discussion Starter · #7 ·
I've never seen or heard of that before. Might be a glitch? You certainly should be able to switch from Mountain Mode back to Normal Mode during regular driving. If you can repeat the events, maybe take a video?
Even though I had drained the battery flat and then built a charge in MM I should have been able to go back to normal mode? Only the gas meter would show up on the display once I left mountain mode. The battery display was nowhere to be found.
 

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Even though I had drained the battery flat and then built a charge in MM I should have been able to go back to normal mode? Only the gas meter would show up on the display once I left mountain mode. The battery display was nowhere to be found.
Okay, that's normal. That's back to the accounting discussion we just had. If you were looking at the DIC power flow screen or the center console energy flow animation, you'd see that even though the gas gauge was shown, once you went back to "normal" mode, the car turned off the engine for the next dozen miles or so to drain the battery of the energy the engine put in it.

You made it sound like the car refused to change to normal mode when you hit the mode button. Note that with the exception of Hold mode, you can be in either the battery screen or the gas screen while in any drive mode - and the engine can be on or off while in "gas mode, sometimes for extended periods.
 

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Discussion Starter · #9 ·
Okay, that's normal. That's back to the accounting discussion we just had. If you were looking at the DIC power flow screen or the center console energy flow animation, you'd see that even though the gas gauge was shown, once you went back to "normal" mode, the car turned off the engine for the next dozen miles or so to drain the battery of the energy the engine put in it.

You made it sound like the car refused to change to normal mode when you hit the mode button. Note that with the exception of Hold mode, you can be in either the battery screen or the gas screen while in any drive mode - and the engine can be on or off while in "gas mode, sometimes for extended periods.
I'm not sure if were understanding each other. Normal mode was not an option I could go to, it was grayed out. I could only go to Hold, sport or MM.
 

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I'm not sure if were understanding each other. Normal mode was not an option I could go to, it was grayed out. I could only go to Hold, sport or MM.
You're right, I'm confused. When you said that only the gas display would show up when you left mountain mode, that made me think you'd switched back to normal mode successfully.

As far as the battery management is concerned, Sport and Normal are exactly the same. I've never heard of Normal being greyed out. I'm told the Hold gets greyed out when you drain the battery all the way...

Not getting the battery screen when you leave Mountain mode is normal. Not being able to select Normal mode isn't.
 

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Not to oversimplify things, but use mountain mode if you are driving up and down mountains. Use normal mode for most other situations. Hold mode is useful if you have a commute that starts out as highway, then hits city driving, and you know you will run out of charge for the full trip. My commute is 18 miles highway, then 7 miles city traffic to work, then reverse on the return trip. Before volts had hold mode, one would blow all their battery before switching to fuel when it would be more efficient to use fuel during the highway miles normal with all sorts of regen for stop lights in the city. Then I'd use battery all the way home until it ran out.

Since I live in flat IL, I've never had occasion to use mountain mode. Plus the grayling of normal mode sounds like a problem. Hopefully plugging it in all night might reset things. Another thing to try is locking the car and taking the keys out of range for a period of time.
 

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personally i found using mountain mode to force the engine to run allows me to get home using about .25 gal less then if I use normal or hold mode for my 35 mile trip
 

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I use Mountain when my battery is out and I'm cruising on the highway. If conditions are right I get a 1/2 charge, then switch to Normal when I'm 10-15miles from home and drive the rest of the way on battery power.
 

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I use Mountain when my battery is out and I'm cruising on the highway. If conditions are right I get a 1/2 charge, then switch to Normal when I'm 10-15miles from home and drive the rest of the way on battery power.
But does cruising in mountain mode generating electricity then switching to normal mode gain you any mileage vs. driving home in normal mode? The law of conservation of energy makes me think you can't possibly be saving gas unless something else is at play here.
 

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If you use Mountain mode from a completely discharged battery to get back up to 40% or 50% charge, then go back to normal mode, the gas icon will stay lit up and all those miles will count as engine miles, because that energy was derived from the gasoline instead of from an electrical outlet.

Also, using MM to charge your battery back up is definitely less efficient, for reasons that have been described here before.
 

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Agreed. Mountain mode is really only useful for building a power buffer for climbing steep and lengthy hills. Otherwise the fuel it consumes is not really worth the charge you get, which by the way seems to vary between years (~35% on 11 and 12, ~45/50% on 13). If you have a choice, stay out of MM when it isn't absolutely necessary. As to the greyed out battery meter, switching to mountain mode will recharge (as previously mentioned) and still give you those miles, but the meter will not revert to the normal green bars until the vehicle is power cycled. The only time I've seen this not be the case was in situations where MM was engaged before the battery drops below 5% (including ICE warm-up time - ie: starting at approximately 8%, but dropping below 5% battery before the ICE enters normal operation will still result in the greyed out battery and 0 miles/km range displayed). If you start MM before this point, the meter will return to green when Normal mode is reselected. In addition, you will also see the estimated range slowly increase as the battery charge increases.
No clue on the greyed out Normal mode. You'd think that since it is the "default" operating mode that Normal would always be available short of some sort of failure/CEL code present.
 

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I use Mountain when my battery is out and I'm cruising on the highway. If conditions are right I get a 1/2 charge, then switch to Normal when I'm 10-15miles from home and drive the rest of the way on battery power.
As many others have said, this is exactly what you don't want to use MM for. Generating electricity, storing it in the battery and using it later on ALL have losses. That's why the Volt has the extra clutch to allow engine torque to go to the wheels without making side trips to electricity. MM should be turned on BEFORE you discharge the battery.
 

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But does cruising in mountain mode generating electricity then switching to normal mode gain you any mileage vs. driving home in normal mode? The law of conservation of energy makes me think you can't possibly be saving gas unless something else is at play here.
This answer is very complicated. The efficiency of the engine at converting fuel into mechanical motion varies depending on the RPM it is operating at; at different speeds and engine RPM, the percentage of power that can go mechanically to the wheels instead of going through a double conversion to electricity and back (losing a little as heat each way) varies, and there's a penalty for putting power into and out of the battery, too.

The ultimate answer is that it is possible to beat the car's default programming with mountain mode cycling games under some circumstances, but you have to be very skilled at doing it, and most people who try actually end up burning more gas than the car would have if they'd left It alone.
 

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But does cruising in mountain mode generating electricity then switching to normal mode gain you any mileage vs. driving home in normal mode? The law of conservation of energy makes me think you can't possibly be saving gas unless something else is at play here.
There were some slight declines in the terrain. Within 10 miles I had half of a charge. In normal mode with regen braking I wouldn't have gained anything...maybe 1 mile.

Not sure if this is the most efficient way (car is still new to me), but I switched back to normal and it showed 14 mile and the battery icon, not gas.
 

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See, that's where I got confused. I could not switch back to normal mode. I had completely drained the battery, went to mountain mode and built up a half charge, but I could not switch back to normal. It was not an option on the drive mode display, it was dark. Even after I turned the car off and back on, I couldn't switch back to normal.
Although I am not in a position to duplicate your scenario, I believe that the system recognizes that the electricity stored in the battery has come from the ICE/generator and, so, will not display it on the screen as it normally would if that electricity had come from external charging or brake regeneration. The electricity is still in the battery for use, but the system will not show it to you as stored battery charge, since it was generated in MM, (which had added charge to reach the higher battery charge level). I believe that if you select NORMAL or SPORT at this point, the system will allow electric driving with the ICE/generator off until the battery again reaches the predetermined "empty" level of charge, which is at the roughly 23% level as opposed to 40% to 50% level required by MM, and the system will continue to operate the car in the usual "battery depleted" mode, cycling the ICE/generator on and off to maintain the minimum charge level of about 23%.

Why your system offers you SPORT, which is essentially NORMAL, but with a remapped "go" peddle, but not NORMAL itself is puzzling. Did you select SPORT to find out what you would get?

When I am starting out on a long trip, I immediately select MM. The system shows a reduced battery range and I drive on battery until I reach that distance, at which point the system switches over to ICE/generator electric driving and the display switches from the battery charge to the gas pump. When I am about 12-13 miles from my destination, I switch back to NORMAL and drive on battery power alone. The display switches from gas pump back to battery charge with range showing 12-13 miles left. I arrive either with the battery depleted completely, or with 1-2 miles range left, if there was recharging due to regeneration from braking.

Although I have driven in NORMAL mode to the point where the car switched to ICE/generator (roughly 23% of battery capacity) and then switched to MM and discovered how that action added additional electricity to the battery by continuously running the ICE/generator to reach 40%-50% of battery capacity, I don't recall if the system prevented me from then selecting NORMAL. It seems logical that I would be allowed to, but that the display would remain showing the gas pump, since I would be driving on electricity from the ICE/generator.

Perhaps your Volt adviser might be able to find the answer to your experience.
 
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