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Discussion Starter · #1 ·
I just got a 2018 Clarity PHEV and decided to take it with me on roughly a 250 mile drive today. The drive was mostly highway and I did have the AC on for the first bit since it is hot where I am. I put the Clarity in HV mode when I got on the highway since I had seen that I should do that. I ended up having to fill up my tank at about 200 miles in since the warning light came on. It took over 6.5 gallons so I know I was pretty close to being empty. Is it normal to only get 30 MPG on the highway? Everything I read was saying I should get at least 40.

In addition, while travelling at low speeds I would sometimes hear the engine revving pretty high while accelerating slowly. Is there a reason why the car does that?

Thanks!

edit: ECON was on with HV as well and before I left it said I would be able to get over 340 in total range.
 

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If the engine is both driving the vehicle and at the same time charging the high voltage battery it can rev pretty high.

The mileage estimator accounts for charging via the J-1772 socket. My son is super eco conscious and always fills the HV battery while at school. The estimated range was 7xx when my wife and I borrowed it over the weekend. There is no way you will get that if you use the approx 50 mi EV and then continue to use up the tank of gas.
 

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Discussion Starter · #3 ·
If the engine is both driving the vehicle and at the same time charging the high voltage battery it can rev pretty high.

The mileage estimator accounts for charging via the J-1772 socket. My son is super eco conscious and always fills the HV battery while at school. The estimated range was 7xx when my wife and I borrowed it over the weekend. There is no way you will get that if you use the approx 50 mi EV and then continue to use up the tank of gas.
While driving, the battery never got below 50% which I am guessing was due to the battery being recharged by the engine. Would that cause the highway MPG to drop to 30 though or might they be separate things?
 

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When HV mode is activated (by push of the button just under the climate controls) the car will maintain the current HV battery level. We hardly pay attention to the MPGs I'm afraid our other car has a 4.8 L V8 that likes (says 93 min on the fuel filler door) 93 octane fuel. We pay roughly $100 per week to keep the tank full on that car so this is super eco in comparison. Running in HV mode is basically driving like a hybrid vehicle. The car is heavy (4000 lbs aka 2 tons) so I'm not surprised that is what you observed.

Hopefully others will chime in maybe later in the morning....
 

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I just got a 2018 Clarity PHEV and decided to take it with me on roughly a 250 mile drive today. The drive was mostly highway and I did have the AC on for the first bit since it is hot where I am. I put the Clarity in HV mode when I got on the highway since I had seen that I should do that. I ended up having to fill up my tank at about 200 miles in since the warning light came on. It took over 6.5 gallons so I know I was pretty close to being empty. Is it normal to only get 30 MPG on the highway? Everything I read was saying I should get at least 40.

In addition, while travelling at low speeds I would sometimes hear the engine revving pretty high while accelerating slowly. Is there a reason why the car does that?

Thanks!

edit: ECON was on with HV as well and before I left it said I would be able to get over 340 in total range.
We've had our 2018 Clarity on several longer trips. I switch to HV on the highway and usually cruise at 70 - 75mph with the AC running (Texas hot). My mpg is usually in the high 30s on those trips when I use very little EV. I have noticed that driving into a headwind or hilly terrain can make a significant difference.
 

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While driving, the battery never got below 50% which I am guessing was due to the battery being recharged by the engine. Would that cause the highway MPG to drop to 30 though or might they be separate things?
Yes. Based on what I saw last month driving cross country, charging the battery from the ICE will cost you up to 20% of your fuel estimates.
 
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Yes. Based on what I saw last month driving cross country, charging the battery from the ICE will cost you up to 20% of your fuel estimates.
But if I remember correctly you were using HV Charge. I don't think they were using HV Charge, they only said they were driving in HV.

While driving, the battery never got below 50% which I am guessing was due to the battery being recharged by the engine. Would that cause the highway MPG to drop to 30 though or might they be separate things?
When you switch to HV mode you are essentially telling the system to keep the EV range where it was when you switched to HV. This is sometimes referred to as the set point. It will then start using a combination of gas and battery. Whenever the EV range drops below the set point, the gas engine will recharge it to bring it back to the set point. This is normal and how it always works in HV mode, the battery is constantly being drawn from and then immediately recharged.

Just to make sure we understand your situation, I assume that you started with a full tank of gas when you started out on the trip in HV mode. You then drove for 200 miles and then filled up with 6.5 gallons. Normally for highway driving you would expect to get around 250 miles on 6.5 gallons. However headwinds can make a big difference. As can hills. Also speed has a large effect on mpg, how fast were you going? AC has some effect but it's not usually that much. Either way just one trip is not enough data to be conclusive, try this more than once preferably in different types of driving conditions.
 

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an important thing to get familiar with about the Clarity, below about 46mph, in HV mode, the ICE will be acting as a generator to create electricity that goes to the traction (electric) motors to move the car. So the engine RPM will change based on need for electricity, not the speed of the car. It can be unnerving and seem noisy. Above about 46mph, the ICE mechanically drives the wheels.

My approach, whenever possible, for best efficiency and enjoyable driving, go to EV mode anytime you drop below 46mph, go back into HV mode once you are above that speed.
 

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My approach, whenever possible, for best efficiency and enjoyable driving, go to EV mode anytime you drop below 46mph, go back into HV mode once you are above that speed.
I personally think that for best efficiency you just quit messing with the button and let the vehicle manage things. By switching it manually you are saying that you somehow can make it more efficient than the way the engineers designed it. I’m not saying that there is never a reason to switch to HV mode, just that in most cases the best solution is to let the car manage it.
 

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I personally think that for best efficiency you just quit messing with the button and let the vehicle manage things. By switching it manually you are saying that you somehow can make it more efficient than the way the engineers designed it. I’m not saying that there is never a reason to switch to HV mode, just that in most cases the best solution is to let the car manage it.
I don't agree, the HV mode is designed to operate the way it does (as a generator) automatically at low speeds when the Traction Battery is depleted, not because it is the most efficient.

the lower speed use of the ICE to generate electricity and drive the car is required by the lack of a transmission.

excess Traction Battery (more than enough to complete your drive and recharge): EV always the most efficient (sort of obvious).
limited Traction Battery (some HV mode required by your drive): EV mode below 46mph, HV mode above 46mph until you have excess battery, then EV mode the rest of the drive.
 

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Discussion Starter · #11 ·
When HV mode is activated (by push of the button just under the climate controls) the car will maintain the current HV battery level. We hardly pay attention to the MPGs I'm afraid our other car has a 4.8 L V8 that likes (says 93 min on the fuel filler door) 93 octane fuel. We pay roughly $100 per week to keep the tank full on that car so this is super eco in comparison. Running in HV mode is basically driving like a hybrid vehicle. The car is heavy (4000 lbs aka 2 tons) so I'm not surprised that is what you observed.

Hopefully others will chime in maybe later in the morning....
We've had our 2018 Clarity on several longer trips. I switch to HV on the highway and usually cruise at 70 - 75mph with the AC running (Texas hot). My mpg is usually in the high 30s on those trips when I use very little EV. I have noticed that driving into a headwind or hilly terrain can make a significant difference.
I was probably going more 80-85 but where I am at is relatively flat. Could that possibly be what affected my MPG so much?
 

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Discussion Starter · #13 ·
But if I remember correctly you were using HV Charge. I don't think they were using HV Charge, they only said they were driving in HV.


When you switch to HV mode you are essentially telling the system to keep the EV range where it was when you switched to HV. This is sometimes referred to as the set point. It will then start using a combination of gas and battery. Whenever the EV range drops below the set point, the gas engine will recharge it to bring it back to the set point. This is normal and how it always works in HV mode, the battery is constantly being drawn from and then immediately recharged.

Just to make sure we understand your situation, I assume that you started with a full tank of gas when you started out on the trip in HV mode. You then drove for 200 miles and then filled up with 6.5 gallons. Normally for highway driving you would expect to get around 250 miles on 6.5 gallons. However headwinds can make a big difference. As can hills. Also speed has a large effect on mpg, how fast were you going? AC has some effect but it's not usually that much. Either way just one trip is not enough data to be conclusive, try this more than once preferably in different types of driving conditions.
I started with a full tank, drove about 3 miles on city streets, then it was pretty much all highway speeds until the last 3 miles while getting home. I had to get gas about 30 miles away from my house so I almost exclusively was going at highway speeds. I don't believe it was windy and I am in a relatively flat area but I was definitely going above 80 MPH for a while. Guessing I just need to slow down then. Just wanted to post and get opinions since I have 7 days and 400 miles to decide if I like the car. But if it is more a user error issue then I am totally happy and just need to adjust my habits. Just didn't want to end up with something that potentially had issues. Thanks!
 

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Discussion Starter · #14 ·
an important thing to get familiar with about the Clarity, below about 46mph, in HV mode, the ICE will be acting as a generator to create electricity that goes to the traction (electric) motors to move the car. So the engine RPM will change based on need for electricity, not the speed of the car. It can be unnerving and seem noisy. Above about 46mph, the ICE mechanically drives the wheels.

My approach, whenever possible, for best efficiency and enjoyable driving, go to EV mode anytime you drop below 46mph, go back into HV mode once you are above that speed.
Awesome thanks for the tip! The high RPMs were at about 20 MPH so that might explain the noisiness.
 

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Any idea on what might have caused the battery to need so much charging in HV mode on the highway?
I had let the battery drop and was recharging before entering areas I anticipated needing both battery and gas for power. As for the battery drop - neither my Volt nor my wife's Clarity do a real good job recovering battery power after the car needs it during extended high speed driving, so the battery drops even in HV (not charge) mode.
 

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unlimited Traction Battery (enough to complete your drive and recharge): EV always the most efficient (sort of obvious).
limited Traction Battery (some HV mode required by your drive): EV mode below 46mph, HV mode above 46mph unless you have excess battery and can use more EV mode.
I think that is possibly true but it's difficult to quantify how much more efficient it might be to use one method or another without doing several controlled tests on a repeated route, and using the odometer and gas purchase receipts to do the calculations.

I think most people pretty much drive that way anyway in the situation that you are describing, which is when someone knows that they will be driving farther than their EV range. If you don't press any buttons it will use up all of the EV at the beginning of the trip, then it will automatically switch to HV where it will remain for the rest of the trip. On surface streets (i.e. stoplights and stop signs) is when you mostly hear the engine, whereas once you are at cruising speed on a highway you barely hear the engine over the wind and road noise. So for drive enjoyment if nothing else, it seems that most people start out in EV until they get on the highway/freeway, at which point they switch to HV, then switch to EV when they exit the freeway at their destination so that surface street driving at the destination is more pleasant. Then do the same on the return trip. However in many cases this will give you a surplus of EV miles, and ideally you want to arrive home with close to 0 miles, so some of the EV miles will need to be used up during the highway portion of the trip. Normally that's done sometime during the return trip when you have a better idea of how much EV range you have left.

Managing things at least to that level is probably somewhat more efficient also, because during highway driving in HV the car will often go into direct drive mode, which is when the gas engine directly powers the wheels using a single overdrive gear. There is no shifting involved, just a clutch that either engages or disengages the overdrive gear. You can see this on the energy screen which shows where the power is going, a little tiny gear appears on the display whenever it is in direct drive mode.

However one thing you will notice when watching the energy screen is that it constantly pops in and out of direct drive mode, basically any time there is any change in power needed, as direct drive only works when the power demand is steady. So that means that even at highway speeds the engine will still be acting like a generator part of the time, and directly driving the wheels at other times. And sometimes even shutting off completely and switching to EV mode for a brief period, even a highway speeds it will do that. But I'm sure it's more efficient to be in direct drive as much as possible otherwise they would not have included that functionality. The Chevy Volt did something similar (obermd correct me if I am wrong about that).

Anyway while I don't mind the three or four button pushes per trip required to use the method that I described, I think I am with ClarityDave that I'm probably not going to be switching in and out of HV any more than that to try and optimize it further. That's great that you do that, would be interesting to know how much additional efficiency can actually be gained.
 

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I learned to put the car in HV mode as soon as I start on a long drive if I know I'll want battery at the end of the drive, or even during it.

And yes, the Chevy Volt (both generations) will do a direct drive connection to the wheels under some situations. This isn't documented well for the Gen 1 Volts, which the Clarity is closer to, but is documented for the Gen 2 Volts.
 
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