HV Only Gas Mileage

Discussion in 'Clarity' started by David Towle, Dec 15, 2018.

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  1. David Towle

    David Towle Well-Known Member

    I would like folks to post their HV only gas mileage, calculated as follows:
    1. Run the battery down on EV with a full tank of gas.
    2. Reset a trip odometer when the engine starts.
    3. Refill the tank before you charge up.
    4. Divide trip odometer miles by gallons of gas to refill.
    5. Describe general temperatures, snow or regular tires, type of driving.

    I just got 38 mpg with temperatures in the 20s, no precipitation, snow tires, and highway driving around 72 mph.
    I should personally generate a number of samples now that I've started my ski season.
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  3. KentuckyKen

    KentuckyKen Well-Known Member

    I went about it from the reverse of what you asked for. Started with a full charge and took the whole trip in HV. Then on each leg, recorded miles, gals, and a small top off charge to get back to full SOC.
    I think most agree that having a significant SOC makes for better economy and driving experience since it allows the algorithm more freedom to choose between all its power flows as needed. Driving on a depleted battery, especially on hills, is asking for the angry bees and lower economy IMHO.

    Lexington KY to Elizabethton TN. I-75 south to Corbin KY then back roads, mostly 4 lane with some traffic lights, to Interstate to Johnson City and 4 lane to Elizabethton. Round trip (~500 miles) so elevation change taken care of. Driver only, high 70s-low 80s with AC at 72 F, 70-75 mph on Interstate, 60-65 on backroads (kept to speed limits).

    Calculated 49 mpg and after accounting for top off charges (only lost 1 bar each way) it was 48 mpg.

    BTW, no angry bees, every power flow possible seen on the display, and only time I heard the ICE was on one long steep hill and even then it was only a moderate rpm range. My car is perfect and I have only had the HV Range update done (afraid the other updates might mess up a good thing). Couldn’t be happier.
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  4. Viking79

    Viking79 Well-Known Member

    I get about 40 mpg around 75 to 80 mph, 45 mpg at 70 mph. Worst is about 35 mpg in really cold weather. I suppose we have put 10,000 miles on road trips so have a really good feel for how well it does.
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  5. Electra

    Electra Active Member

    David, do the test again with a full battery and a half battery to see if you get better numbers.
    KentuckyKen likes this.
  6. Sandroad

    Sandroad Well-Known Member

    But, but, but........this is not the way the Clarity works best, as we've learned from almost a year's worth of posts on this forum. My Clarity is a joy to drive on electric around town and with enough SOC in the main battery to boost acceleration when needed using the gas engine in HV on the highway. I would never purposefully run the main battery down to 0 on my Clarity and then expect the car to perform well and with peak efficiency, either in town or on the highway. Further, the list of things affecting MPG is very long; it goes way beyond temp, speed, tires and precipitation. Wind direction, wind speed, traffic, hills, weight in vehicle, driving style, HVAC use, etc. etc., all come to mind.

    I'm sure I'm overthinking it, but I really do believe the Clarity was designed with a great balance of EV and ICE operation and using either one exclusive of the other defeats its design.
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  8. David Towle

    David Towle Well-Known Member

    Well it may not be the way the Clarity works best but it is the way its designed. You start up in EV and it runs in EV until out of electrons then it goes to HV. It works fine this way and I have never yet experienced angry bees. You have to intervene to get it to do something different.
    That being said I'm 90% sure I'm going to VT again tomorrow so I will go right into HV at startup and run a comparison and report on it.
  9. David Towle

    David Towle Well-Known Member

    These are all calculated odometer/gas pump numbers not from the car's calculations right?
  10. David Towle

    David Towle Well-Known Member

    I hear the ICE every time it comes on, not a problem. You must blast your music good!
  11. KentuckyKen

    KentuckyKen Well-Known Member

    Maybe the problem is I blasted it in my youth and am paying for it now. But even with the hearing aids turned up I can barely hear it. My ICE just doesn’t rev up, but then I’m in a fairly flat area with just rolling hills and speeds under 75 mph (and mostly under 60).
    My car is library, hear a pin drop quiet. If not for my hour meter, I would miss some of the ICE operations. It’s that quiet. “Can you hear me now?”
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  13. Clarity_Newbie

    Clarity_Newbie Active Member

    David Towle

    I happen to have done this a couple months ago out of curiosity.

    My spreadsheet shows 217 miles and filled up with 4.23 gals for 51.3 mpg If memory serves me correct it was in the 60's to low 70's. Running OEM tires. Miles accumulated over 4 days driving regular route which is mostly urban 2 and 4 lane roads. Negligible Interstate miles. Rolling to some elevation gain/loss. 35 to 60 mph is the norm.

    I run HV mode purposely several times a month but rarely discharge all the way. I did discharge on purpose last week since I am ciphering on the clutch engagement while in HV mode since the updates in October.

    My current tank I filled up with 89 octane non-ethanol gas so I should see some difference vs "up to 10%" ethanol I've run in the past.

    Hope this helps.

    Good luck.
  14. Viking79

    Viking79 Well-Known Member

    Correct, and only times I could calculate because of no EV usage. Like driving IA-GA and back I was between 42 and 45 mpg between 70 an 75 mph. Moderate temps. Driving IA-WY and back between 39 and 42 mpg around 75-80 mph. Similar drives several times. Worst was a trip to Omaha around 35 mpg at 75 mph, but it was winter, I don't think car was in Atkinson cycle as much, maybe heavy heater use or something.
  15. DaleL

    DaleL Active Member

    On a 2,000 mile round trip from Florida to Ohio, subtracting out EV miles, I got 43 mpg. Almost all of this was highway miles at between 65 and 75 mph. Because of the small 7 gallon tank, I kept about 30 miles of EV range in reserve. It turns out that was wise as the car benefits from having reserve battery power when driving in the mountains.
  16. David Towle

    David Towle Well-Known Member

    I tested again with a full battery and things got worse and interesting. Did two measurements each on about 3/4 of a tank and got as follows:

    Run 1. 98% on highway at 72-73 mph with cruise set wherever possible. Temps in the 30s and 40s, no precipitation, total weight of 250 lbs in the car, started with full battery. Got 33 mpg actual, 38 indicated by the bogus dash reading. Did gain about 500 ft in altitude start to finish.

    Run 2. 1/3 on local 2 lanes averaging about 40 mph, 1/3 on highway at 72-73 with cruise, 1/3 in moderate rain on highway averaging about 62, so overall average about 55 mph. Temps in the 30s and 40s, average battery 3/4. Got 37 actual mpg, 43 by bogus dash reading. Lost 500 ft in altitude.

    I'm quite disappointed in these numbers. I had been suspicious mpg was too low since I got the car but even though I've put over 4000 miles on it in 2 months these were my first chances to calculate just HV mileage. Testing under warmer conditions will have to wait till next summer.

    In addition to the above I also experienced angry bees for the first time under very surprising conditions. About 5 miles after leaving the ski area I was driving downhill, at about 45 mph, with the battery about 3/4 full and suddenly the revs rose way up. Power was not an issue since I was going downhill but just to speed up a few mph required an incredible amount of revs. I switched to EV and back to HV but it returned. Over about 5 miles it gradually subsided and went back to normal.

    The horrible cruise control is clearly partially responsible for the low mileage, but unfortunately I have a lot of cramping problems with my feet and have to use it wherever possible. Also it did not go into gear mode very often at all, probably 10% of the time on each of the runs. I was quite surprised there was no benefit at all from a full battery.

    I'm a conservative driver and these numbers hurt my pride! With my previous car (BMW 328 convertible), rated 17 city 27 highway, I was able to average 28 mpg overall year round and on the highway almost always get over 30. I guess all I can hope for is that Honda decides to fix the software so the car operates better but since its been out a year how likely is that?
    Kailani likes this.
  17. Viking79

    Viking79 Well-Known Member

    I wouldn't be too worried about results yet, track it for some time. The elevation change might represent 4 or 5 miles driving on flat ground, would that make a difference in your calculation? Check tire pressures. Also, I am unsure if car runs differently when new vs with some miles or winter vs summer. It looks like the car wasn't using its super efficient mode as often, which might be due to cold weather or elevation changes.

    Down the hill, had you been using regen continuously for those 5 miles? The battery might have been getting too warm, remember, it is like DC fast charging the battery and at 3/4 full it might be putting in a lot of heat. I have seen the argument that the engine runs to counter some of the regen power and this would support that hypothesis. Maybe arrive with less charge in the battery (near empty). It is also possible the battery was very cold, in which case regen might be limited to prevent damage to the battery (lithium plating from charging a cold battery fast).

    I haven't noticed much difference in economy full battery vs empty (2 bars), as the battery has a fairly large buffer built in, so unless you are driving up long steep hills it might not matter, and if it tries to recharge it after it isn't efficient doing that so wouldn't expect much difference. I tend to turn on HV about half just to save some EV for my end point. See what it does in slightly warmer weather or maybe adjust your heater usage to see if it makes a difference (the engine is fairly thermally efficient, so it might not generate enough usable heat unless it runs in a less efficient mode).

    Finally, what are your tire pressures? I usually run 35 or something, so nothing particularly high.
    Last edited: Dec 17, 2018
  18. Linkmodo

    Linkmodo Member

    One thing I know for sure, HV Charge Mode my clarity's mpg is 20mpg with car running at 65-70mph on hwy. :D

    I don't really understand why would they put a HV Charge mode there it's actually very inefficient. HV mode my mpg is around 40-43, 70F florida weather.

    Owned the car for a month, put 1000 miles on it, only filled 10 gallons of gas because had some long hwy driving in HV mode. Rest of the time the car is on EV only. My mpg indicator says my EV/HV combined mpg is around 70-90, I'm sure it's quite inaccurate.. My old Accord V6 would have burned 50+ gallons of gas for the same distance...
  19. David Towle

    David Towle Well-Known Member

    No 4 or 5 miles don't make a real difference.

    It was only a slight hill I was going down, enough that some gas pedal input was required to keep the car at speed.

    I don't understand how the engine running fast and putting more energy into the battery would counter regen which is also putting energy into the battery.

    I wasn't using much heat, I keep the fan on low and it was not very cold. The engine generates plenty of heat anyway, yes its high efficiency at 40% but that still leaves 60% that goes to heat and a good fraction of that goes into the water.

    Tire pressures all at the recommended 36.
  20. Chuck

    Chuck Member

    As far as the HV Charge Mode my only guess is that Honda thought the Clarity would be sold in Europe or that US cities would start adopting policies like some Europe cities. London charges almost 12 pounds a day to drive in the city UNLESS you are an EV or PHEV. People would want to make sure they have enough juice to make it thru town. Don't ask me how they police it but I do know they have IR cameras that look for exhaust.
    David Towle likes this.
  21. neal adkins

    neal adkins Active Member

    Hv charge is an option that allows you to charge the battery before driving on long uphill/grade road or before city driving. I use hv charge when going down a mountain to regain lost charge as well.
    insightman likes this.
  22. Not sure why that would be necessary. I get lots of regen just coasting down hills and/or using the paddles as appropriate.
  23. MNSteve

    MNSteve Well-Known Member

    Question for you mountain dwellers: Do you see your EV range actually increase after a long period of downhill driving? I've never seen any tangible indication that regen is capturing anything other than the power indicator dipping into the "charge" range.

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