GM Volt Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
144 Posts
Discussion Starter · #1 ·
I'm driving from North Texas to Disney in FL this weekend, and having only taken one relatively short road trip from DFW to Austin, I have only a vague idea of what speed will maximize CS fuel economy. On my trip to Austin, I burned most of a tank each way, but started with a full charge. I got 50MPG combined on the way down (at night, only a little AC for defroster) and 45MPG combined on the way home (daytime, more AC, headwind, higher speeds).

I'm aware that the ICE will lock into the planetary gearset in CS or Hold mode above a certain speed, but I'm not sure what it is. I gather that it also depends on load. On the TX->FL and back trip, it will be mostly flat, straight roads, so I should be able to maintain a pretty steady velocity with the cruise. I don't plan on plodding along at 50 MPH on I-20 (I don't want to die), but if I'm going to get significantly better mileage at 60MPH than 70MPH, then I'll be a right-lane turtle to see how high I can get on this inaugural epic road trip.

Anyone got any reliable stats to build a picture of what to expect?
 

·
Registered
Joined
·
144 Posts
Discussion Starter · #2 ·

·
Registered
Joined
·
175 Posts
Can't give you an answer there, but I was down a few weeks ago and got about 38+ mpg on the trip from the ICE, and that was at 75+ mph - with two people in the car. You hover at 70 -75, I suspect you will do significantly better.
 

·
Registered
Joined
·
5,486 Posts
42 mpg for me last week on the the return leg of a 700 mile round trip on the CS-mode portion going 65 mph or so. You can get better mpg going slower, of course.
 

·
Registered
Joined
·
117 Posts
My second day with our volt we went from Northern Virginia to Orlando Fl (Disney) and the first tank with full battery was high 50's. Second and 3rd tank with no battery was high 30's. I was also using cruise, a/c and car loaded down with 2 adults, stroller and the kid going 78mph. Still not bad at all IMO.

But if your able to charge overnight at hotels along the way, you'll definitely increase millage.
I have a 200mile trip coming up in a few weeks only 40% highway, and Ill see if I can manage to keep it at around 55-60mph and increase the MPG.
 

·
Registered
Joined
·
41 Posts
I spend a lot of time toodling around Houston on EV mode (I am right around 200mpg), but I have a trip to NW Arkansas coming up which I have driven in a rental Malibu at an average speed of 71mph (including stops for gas and potty breaks). The trip includes a bunch of 55mph zones and traffic lights, so 71 is haulin'.

On our trip in the Volt I expect to cruise at 70mph and take the 55mph zones in stride at 5 over. I'll be interested to see what I get.
 

·
Registered
Joined
·
1,650 Posts
Just as others have said, and as the graph referenced in the thread you linked indicated, the slower you go the better the efficiency. To answer your question about when the ICE clutches to the wheels, it is any time there is low load above around 35 mph, so at almost any speed that you set the cruise control in CS mode, you will be in power split mode, with the ICE clutched to the wheels. If you are ever curious, floor the accelerator. If there is a long delay, one or two seconds, before you get significant acceleration, you were in power split mode. The hesitation was the powertrain getting out of power split mode to accelerate. I hope GM will try to reduce that delay in Voltec 2.0.
 

·
Super Moderator
Joined
·
6,380 Posts
Just found this other thread (no idea why I couldn't find it before!) - reading it now...
http://gm-volt.com/forum/showthread.php?12304-What-s-the-most-efficient-highway-speed
I went a couple hundred miles to day at 65 MPH on cruise. Temp Mid 60's there and low 70's home. I got 42 MPG a few minutes after the engine warmed up. That is after my battery ran down and the ICE ran for a couple minutes (ICE temp hit 130 on its way to 160+) I then reset my B trip odometer. Anything above 40 is outstanding as far as I am concerned!! I used a Scangauge device to see instance MPG as well and it is interesting to watch 1500 rpm compared to 2000 rpm.
 

·
Registered
Joined
·
5,410 Posts
As your ICE gets broken in...your numbers will go up...providing you're not trying to drive 80+...:)
 

·
Registered
Joined
·
340 Posts
My experience doesn't quite reach the levels of others. I find if I go a steady 65 MPH, I get about 38 or 39 MPG. I don't get over 40 unless I drop to 60 MPH.

It does help in my experience to follow a tractor trailer, if you ever want to try it. I've tested that a time or two. You don't have to get too close to get a boost. Just find one to follow that is going the speed you want to go, and make sure it's clean (following one covered in rocks and dirt is a bad idea)
 

·
Banned
Joined
·
34 Posts
I did some cs miles at up to 73 mph and got 42mpg. I was only moderately happy with that given that the Prius claims as much as 51 mpg but I guess not at that speed. My current diesel get 45-48 driving like a hotrod.
Temp was in the 60s and I had windows open a little with no ac or fan running.
 

·
Registered
Joined
·
144 Posts
Discussion Starter · #12 ·
Thanks for the info everyone. I have learned how there isn't a specific magic speed where the ICE locks into the ring gear, but it's based on load, which is dictated by several factors - current speed, wind drag, rolling resistance, AC/heat load (electrical), and throttle position. Sounds like if I can maintain a steady, reasonable speed on flat ground without having to crank the AC, and perhaps take a draft off a caravan or big rig (at a safe distance of course), then I should easily be able to achieve 40+ MPG. I was able to get those sorts of numbers in my wife's 2002 Saturn SL2 on a trip to NW TN a few years back with these techniques, and it's rated lower than the Volt on the hwy by the EPA. The old adage of "slow and steady" comes to mind, but it's tempting to just mash it and do 75 and get there an hour and a half earlier. :p
 

·
Registered
Joined
·
1,567 Posts
It does help in my experience to follow a tractor trailer, if you ever want to try it. I've tested that a time or two. You don't have to get too close to get a boost. Just find one to follow that is going the speed you want to go, and make sure it's clean (following one covered in rocks and dirt is a bad idea)
I noticed a big boost in my 3/4 ton yukon staying behind tractor trailers. About 1.5 second follow distance was good for an extra 1.5 mpg. 2 second follow distance lost it. I wasn't comfortable staying closer than that. When you are only getting 13 mpg a 1.5 boost is a big deal! However I did suffer greatly from rock chips - it inspired me to install a bug deflector on the front of the hood after touching up all the chips.

I haven't tried it with the Volt yet but I'd be worried about the debris. And the difference between 38 and 40 isn't worthwhile to me to grab all the crap that flies up behind a big rig - especially knowing how touchy that lower air intake is where a rock chip might be enough to puncture the cooling system.
 

·
Registered
Joined
·
906 Posts
I got close to 45 MPG ICE only in flat ohio going to cleveland and back this past weekend.. my battery was at about 80%.. it seems to me the hold mode works best when there is some battery charge.. it seems to keep the ICE cycles longer than if you just run the battery dead and let the car auto-switch. to me long ICE cycles are better than short.

I was driving 65 MPH except for 60 during the 55 MPH construction zones... I used cruise control all the time... the climate was on fan only, dry and about 60 outside so no A/C or heat was running.. I had the stereo LOUD... and the windows closed..
-Christopher
 

·
Registered
Joined
·
41 Posts
I did some cs miles at up to 73 mph and got 42mpg. I was only moderately happy with that given that the Prius claims as much as 51 mpg but I guess not at that speed. My current diesel get 45-48 driving like a hotrod.
Temp was in the 60s and I had windows open a little with no ac or fan running.
A former 2010 Prius owner here - as you intimated, a Prius gets low 40's running at 70 on cruise control.
 

·
Registered
Joined
·
144 Posts
Discussion Starter · #16 ·
A former 2010 Prius owner here - as you intimated, a Prius gets low 40's running at 70 on cruise control.
1100+ miles on the trip to Florida at 75 most of the way, defrost running most of the time, 39 MPG. No drafting or hypermiling. I have to say I love the torque up hills with cruise control on, no upshifting to maintain speed!
 

·
Registered
Joined
·
6,464 Posts
I've been tracking this somewhat (I still have to gather some more info before I post anything up), but I've found that quite a few factors affect the Volt's CS mileage. Obviously, speed is the single biggest factor, but I've found that octane level and ICE break in also play a role. In a nutshell: Changing my oil (still had over 50% life according to the Volt estimator) resulted in ~ 10% increase in CS fuel economy, and increasing the octane resulted in ~ 5% increase in fuel economy. The latter is a bit tricky, though, as the octane's effect seems to be dependent on engine load and cycle time (i.e., any cycle that burns less than .25 to .5 gallons of gasoline seems unaffected by the octane). However, the increased efficiency of the oil change seems to be almost immediately noticeable, regardless of cycle time.

Obviously, the more the octane levels increase, the more diminished the returns. I haven't mapped out exactly when that occurs in terms of performance, but it happens far earlier in terms of economics (unless you are in an area where 93 octane can be had for about a 5% premium over the lower octane grades). When people finally map the ICE's timing across RPM/Load ranges and start logging ICE cycles, it will be easier to figure out.

A former 2010 Prius owner here - as you intimated, a Prius gets low 40's running at 70 on cruise control.
And this actually brings me to a very interesting (but, currently, anecdotal) conclusion: In steady-state driving, the Volt is as efficient in CS Mode at highway speeds as the Prius. Though the Prius has a more efficient ICE (37%-39% efficient versus 33% for the Volt), the Volt's superior aerodynamics actually overshadows that efficiency difference. And the faster the cars go, the more those numbers skew in the Volt's favor. I'm interested in hearing more, honest accounts of the mileage that Priuses are actually seeing at steady-state driving at 70-75 mph, because those numbers seem very close to what I'm now seeing (post oil change) in my Volt.

I'm not sure exactly what the problem is, but I think that the way the Volt's ICE was prepped (e.g., initial break in) and the way the the EPA test cycle was conducted (e.g., short ICE cycles) both resulted in a poor EPA estimated mileage. After my oil change, a short 18 mile run on flat ground with the cruise control pegged at 55 mph resulted in close to 50 mpg on 91 octane. Pre-oil change, I'd never seen anything close to those numbers (best at that speed with 91 octane was 40-42 mpg). I should have had the original oil tested, but from my personal experience with oil changes, it was far overdue. Anyway, this is a snapshot after I stopped:

 

·
Registered
Joined
·
3,165 Posts
Interesting about the oil impacting MPG.. should be some others here that have changed their oil. Anyone else see a difference. I'm at 21 months so I'll find out soon.

I've already had multiple 50MPG days (over longer distances), which is why I posted a 50/50 club, 50 miles per charge + 50 MPG days. But its a little easier here as the air is thinner up here and I run my tires at 40-42psi. Maybe I can get some 60+MPGdays after the change.
 

·
Registered
Joined
·
2,005 Posts
I've been tracking this somewhat (I still have to gather some more info before I post anything up), but I've found that quite a few factors affect the Volt's CS mileage. Obviously, speed is the single biggest factor, but I've found that octane level and ICE break in also play a role. In a nutshell: Changing my oil (still had over 50% life according to the Volt estimator) resulted in ~ 10% increase in CS fuel economy, and increasing the octane resulted in ~ 5% increase in fuel economy. The latter is a bit tricky, though, as the octane's effect seems to be dependent on engine load and cycle time (i.e., any cycle that burns less than .25 to .5 gallons of gasoline seems unaffected by the octane). However, the increased efficiency of the oil change seems to be almost immediately noticeable, regardless of cycle time.

Obviously, the more the octane levels increase, the more diminished the returns. I haven't mapped out exactly when that occurs in terms of performance, but it happens far earlier in terms of economics (unless you are in an area where 93 octane can be had for about a 5% premium over the lower octane grades). When people finally map the ICE's timing across RPM/Load ranges and start logging ICE cycles, it will be easier to figure out.



And this actually brings me to a very interesting (but, currently, anecdotal) conclusion: In steady-state driving, the Volt is as efficient in CS Mode at highway speeds as the Prius. Though the Prius has a more efficient ICE (37%-39% efficient versus 33% for the Volt), the Volt's superior aerodynamics actually overshadows that efficiency difference. And the faster the cars go, the more those numbers skew in the Volt's favor. I'm interested in hearing more, honest accounts of the mileage that Priuses are actually seeing at steady-state driving at 70-75 mph, because those numbers seem very close to what I'm now seeing (post oil change) in my Volt.

I'm not sure exactly what the problem is, but I think that the way the Volt's ICE was prepped (e.g., initial break in) and the way the the EPA test cycle was conducted (e.g., short ICE cycles) both resulted in a poor EPA estimated mileage. After my oil change, a short 18 mile run on flat ground with the cruise control pegged at 55 mph resulted in close to 50 mpg on 91 octane. Pre-oil change, I'd never seen anything close to those numbers (best at that speed with 91 octane was 40-42 mpg). I should have had the original oil tested, but from my personal experience with oil changes, it was far overdue. Anyway, this is a snapshot after I stopped:
The EPA ratings have always been like this . Every Nissan , Toyota or Honda I've owned has struggled to meet the rating.

Every Ford , GM or VW has exceeded the ratings by around 10% or so .

A Prius uses 5-8 % less fuel than a Volt when in CS mode . It also weighs less , doesn't have the power , torque , great handling or ability to drive 1,000 miles per month without a drop of fuel .


Interesting about the oil impacting MPG.. should be some others here that have changed their oil. Anyone else see a difference. I'm at 21 months so I'll find out soon.

I've already had multiple 50MPG days (over longer distances), which is why I posted a 50/50 club, 50 miles per charge + 50 MPG days. But its a little easier here as the air is thinner up here and I run my tires at 40-42psi. Maybe I can get some 60+MPGdays after the change.
My best has been about 48/46 . I usually only get a 43/43 . I think CO has it's advantages .
 

·
Registered
Joined
·
6,464 Posts
Well, like I said, I think the key to figuring out exactly what is going on with the ICE is data logging. I really want to see the effect of load on the timing map. If we can identify sweet spots in the drag and rolling resistance loads, it will be easier to determine the best speeds for cruising and ideal octane. I know the octane plays a factor, but at typical cruising loads, the difference between 91 and 93 seems to be less than 5% (not financially worth it).
 
1 - 20 of 24 Posts
Top