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If you turn mountain mode on before an uphill grade and start with a 11 to 15 mile "reserve" of battery power, should you turn Mountain Mode off while climbing?

The reason I ask is it seems that if you leave it on, the generator will work overtime to keep the battery at the 11 to 15 miles of battery and it doesn't seem like there should be any difference from just being in CS mode.

What am I missing?
 

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I think it might depend on the "hill". Three days ago I drove up and over Donner Summit on Hwy 80. The summit's altitude is about 7,100 feet. I put the car on mountain mode around Roseville well before the main ascent and it took on the long climb just great with plenty of power.

Going up a much smaller grade going from Truckee to Kings Beach a little later that day I did not put it in mountain mode and the car was sluggish but made it up the grade but at a reduced speed (I think 45-50). The mountain mode definitely works to make the car perform better in mountainous terrain over longer drives. My guess is it might also help the battery life too.
 

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I guess if you could be sure to make it to the top on the reserve battery power alone, then it might make sense to switch back to Normal or Sport mode at the base of the hill. It also depends on what happens at the top of the hill. Will you be at your destination where you can charge? Is it downhill from there? Or will you have to drive level for 50 miles?

Personally I would rather leave it in MM until on the top just to make sure. I've experienced "Reduced propulsion" and didn't enjoy it.
 

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If you turn mountain mode on before an uphill grade and start with a 11 to 15 mile "reserve" of battery power, should you turn Mountain Mode off while climbing?

The reason I ask is it seems that if you leave it on, the generator will work overtime to keep the battery at the 11 to 15 miles of battery and it doesn't seem like there should be any difference from just being in CS mode.

What am I missing?
It depends on where you are, and what you're trying to achieve. Turning MM off will result in the car going back to electric power immediately, and staying electric until it draws down the ~3.5kWh MM holds (depending on how you entered MM, the instrument panel may or may not go back to battery.)

If you leave it on, the engine will try to keep those 3.5 kWh in the battery, yes. That's kinda the whole point - because the real purpose of mountain mode is to give you the full 150 HP to work with for climbing long steep hills at high speeds. If you try to go up one of those hills without MM, the engine will be running as hard as it can - and it still won't be enough - it'll drain through the buffer it keeps in normal mode, and then the battery will lock down at 15% SoC, and you'll be in "Propulsion Power Reduced" (message on the DIC) - trying to climb the hill with the full 86 HP the engine can muster (which often means slowing down to 40-45 MPH, depending on the hill.) Mountain mode gives the car a larger battery reserve, so that even though the engine is still losing ground as you charge up the side of a mountain, there's a big enough buffer that you'll run out of mountain before you run out of buffer. If you switched out of mountain mode at the base of this sort of hill, you'd likely find yourself back in PPR before you reached the top - and after you hit PPR, MM can't do anything for that hill - the engine is already working as hard as it can (if there's another hill behind it, it still might be worth turning on.)
 

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Perfect post for a newbee like me. I was confused when to use mountain mode and if it was worth the reduced MPG's. Now I totally get it and have a new tech term "PPR" which I hope never to experience (it still seems a hundred times better than "turtle mode" on the Leafs)...
 

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Perfect post for a newbee like me. I was confused when to use mountain mode and if it was worth the reduced MPG's. Now I totally get it and have a new tech term "PPR" which I hope never to experience (it still seems a hundred times better than "turtle mode" on the Leafs)...
If you engage mountain mode before you get down below its nominal state of charge, MM has no impact on gas mileage - the car runs the engine in exactly the same way, just with more reserve in the battery. That's the way I use it when I know there'll be a hill somewhere on a trip that's longer than the battery (or when I want to use the rest of the battery at the other end of the trip.)
 

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On of course.
 

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On long hilly highway drives, go up the hills using battery and down the hills and flats using the engine via mountain mode, the engine revs less and you'll get better mileage. Some people don't agree with this though so...

MrEnergyCzar
 

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Would we rather have a smartphone app or the Nav system offer advice on when to use MM.
 

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On long hilly highway drives, go up the hills using battery and down the hills and flats using the engine via mountain mode, the engine revs less and you'll get better mileage. Some people don't agree with this though so...

MrEnergyCzar
Mr. EC, I do agree you'll get better mileage with this strategy vs. not using any MM (and have proven it with data :)). However, in my tests I achieved better MPG and AER by going uphill using ICE and downhill using battery. Both approaches performed better than leaving MM off entirely. But the question comes down to whether the ICE is more efficient when just maintaining the SOC buffer while climbing or rebuilding the SOC buffer while descending. It seems the answer is the former.

Below is the elevation profile of my work commute for the last year. It was a perfect playground for MM games. I performed several tests of each approach minimizing other variables such as ambient temp, climate controls, speed, driving mode, etc. Go to the "My MM Games" link in my sig for details. In short, not using any MM gave me about 136MPG & 31AER (70% electric). Using MM on the decline gave me 151MPG & 36 AER (82% electric). And using MM on the incline gave me 170MPG & 39AER (87% electric). After posting my original results, I repeated several more iterations of each test and the results were consistent when accounting for changes in ambient temps.

Now any time I know I am going to climb and descend, I will engage MM before I get below 15 miles of EER and leave it in MM until I reach the peak. Then switch back to electric for the descent. This produces the best overall efficiency plus keeps you out of reduced propulsion mode (and is the way GM intended MM to be used anyway). Note that the efficiency gains do not apply when you engage MM below 11-14 miles EER. Then the losses of the ICE replenishing the SOC buffer offset the gains, but this still helps keep you from going into reduced power mode on long climbs so is still probably a good idea.

 

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I went on a long trip last week and preferred to use mountain mode until I reached the base of the large hills and switched to sport mode to fly up those hills in EV mode . After I reached the summits , I would switch back to MM .

However , this strategy is not recommended for extended climbing of extreme inclines like Pike's Peak or Independence Pass because you would run out of battery well before you reached the top .
 

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I just leave it in MM, as it can then also clutch the ICE directly and it reduces the peak load on the battery and electric motors.
That direct power from the engine is more efficient, not having to suffer a round trip battery loss and any I2R and eddy current loss in the motors as well. GM pointed this out in one of their documentaries on the drivetrain tech.

Many people are confused about reduced gas mileage. The truth is that reporting it correctly is just about impossible. If the engine is putting power into the batteries as well as pushing the car (net gain in battery charge) then yes, the mileage looks nasty - because it's all charged to gasoline, and when you take that charge back out of the battery, it's all reported as electric miles...even though some of the kWh came from gasoline.

Once you understand that, the actual gas mileage is pretty darn good - you're getting some electric miles that should have been added to the mpg for gasoline, but weren't. Pretty hard to keep track of which kWh came from where, they're all fungibly mixed up in the battery, after all. Kind of like trying to keep track of the basis cost of some stock you bought over years at all different prices. You can do it, but it's pretty difficult.

I have one "hill from hell" I have to climb coming home, when I'm usually also low on battery. I use MM a couple miles before that to pick up a little charge and have a better hill climb when I get to it. It works for me, and I don't burn much gas at all doing that. Depending on my current state of charge - it might instead have gone to CS mode just as I top the last hill and could coast downhill again to my place, which doesn't run the engine long enough to keep it efficient - it doesn't even get fully warmed up when that happens.

I can vouch for the engine being on while climbing. Here's a vid I made the day I got the car from a dealer 55 miles away...this was CS mode, but the same ideas apply. That hill is steeper and longer than it looks. Going down it, foot off the accelerator pedal in sport mode, the speed goes up to the point I have to use the brakes to make the corners...it's really the hill from hell - I could ask for more aggressive regen for it.
http://www.youtube.com/watch?v=flZQ_5mpm3k
 
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