Getting horrible gas mileage on our 2018 Honda Clarity, 25-28 mpg!

[Landshark]

While not "free" it is recovering something that would otherwise be wasted and turned into heat thru the friction brakes. It would not increase the RV fuel consumption, but allow for the capture of that otherwise wasted energy that could then later be utilized or driving, cooking, lighting, etc.

The amount of energy recovered would be minimal, in my experience. We’ve traveled as little as 75 miles and a much as 550 miles in a day. Many motorhome owners have a self imposed 300 mile a day limit. On a day like that, the trip would involve one stop midway for a driver swap and restroom break and a second stop at the final destination. There is very little braking along the way.

the fact that a flat tow could have gain a charge if you get stranded away from charging infrastructure (vs waiting for a tow to a charging station). A primary means of charging?

Well, don’t you have to wait for the flat tow?
What is towing the EV? An ICE vehicle?
Thats like the walk of shame.
If so, the energy stored in the EV was put there by burning fossil fuel.
Is there some level of regen that is set in the EV while it is being towed? If so, that’s more resistance for the towing vehicle to overcome.
How much fuel is being used to tow the EV?What distance must the EV be towed to restore a meaningful amount of charge?

It would probably be easier for a truck to pull up with a 12K generator, burn a gallon of diesel and charge at 40A for an hour.

 

[David Towle]

My understanding, or misunderstanding, of the electric heat in the PHEV is that it is similar to an on demand/tankless/instant water heater. It heats the coolant in the engine coolant loop. Per the manual, there are 1.31 gallons of coolant in the engine cooling system.

Under the sink instant water heaters for residential use draw ~1500 watts. They heat water to 149-167F and can deliver 2.5gpm. Coolant temperatures for ICE vehicles seem to be around 185-210F. I don’t know what temperature Honda targets for the coolant when utilized for cabin heat. 150-160F would seem to be sufficient. I can’t imagine what a 7kW or 14kW heating element would do to 1.31 gallons of coolant.

This reminds me of an interesting question I haven't brought up before, but which doesn't affect me. If you use electric heat in EV, doesn't this system waste a huge amount of heat, maybe half, in engine compartment loss? That hot water you're making has to circulate at least a little by natural convection through the radiator, has to heat up the engine block which then loses heat to the surrounding air, etc. It seems like a terrible way to utilize electric heat compared to an inline electric coil in the hvac system.

 

[David Towle]

Compared to the OP I am enjoying very high mileage in gas only mode since I moved to Florida, burned 6 tanks so far. Alternating HV Charge and EV around town I've been getting 52-54 mpg. On the highway in HV getting 45-48 range. Temperatures in the 50's to 70's. Overall the flat terrain here seems to have bumped up my mpg by about 3 versus hilly CT. Of course I would like to use the cheap electricity here, but we are temporarily in an apartment while our house gets finished with no outdoor outlet that's accessible.

 

[LAF]

Hi, my dad recently purchased a used 2018 Honda Clarity in October and have begun to experience issues with our gas mileage. We live in CT, with the cold we have to charge the battery too frequently and our energy bills had increased by $70. Charging was simply too expensive, so we decided to use it gas only, we thought it would be cheaper but we are getting between 25-28 mpg! When it was advertised to be 40mpg for highway driving.

We decided to double check. And drove the car over the span of a week while noting everything, driving only in HV mode with no battery charge, he filled up the gas tank full before driving for the week. The gas range after he filled up the tank showed that we had a range of 244 miles left on a full tank. But after a week of driving, it shows me that I have 83 miles left on my gas tank. While our odometer read that we had driven for 115 miles (which is accurate)

So the gas range shows that I have driven 161 miles, with 83 miles left on my gas tank after a full tank. While my car odometer reads that I have only driven 115 miles.

The mpg on the car system shows that he only gets 25-28 mpg. And every week we have to fill over 5 gallons of gas in the tank, while my dad drives only 90-110 miles a week. We should have to fill up 2.5-3.0 gallon a week at max.

Thank you for reading, if anyone has faced a similar issue or knows the issue, would love to hear what we can do! Going to take it to a Honda Service center next week to figure it out. Hope they can help. But the MPG we are getting while driving on gas is horrible.

I have to say that the reason to drive EV is a lot more than saving money. Driving is serene. HV driving of this car is really only for the highway.

 

[LAF]

I ran a test with the heater while driving in EV this morning. I covered 14 miles in 15 minutes. One mile of slightly downhill surface streets to the freeway, 13 miles on the freeway at 60-70mph, slightly uphill with a steeper bit on the last half mile. This is the 14th time this year that I have driven this stretch. I may have driven it 100 times since owning the Clarity. Temperature was between 45-50F. Heat was set to Hi at the end of the driveway, fan was on medium, 4th bar.

I’ve made a mental note of EV range at this 14 mike mark on every trip. The remaining 13.5 miles is downhill to flat. I’ve also noted the range while cresting the hill on the return trip. The 47 mile RT has been completed completely in EV at least 95% of the time. That’s the background.

EV range at the top has always been between 28-32 miles. I’ve never used anything other than the drivers seat heater and only occasionally before this test. Today it was 26 miles. From this initial test, I would estimate that the heater consumed 2-6 miles of range. Since the car has been getting 47 miles or more on this trip, I’d estimate that it’s getting ~3.5 miles/kWh. That would be a loss of 0.6-1.7kWh’s over a 15 minute period from using the heater. It’s a pretty wide range, but the possible wattage based on this test would be from 2400-6800 watts.

you are averaging 60 mph- EV best for slower driving

 

[insightman]

This reminds me of an interesting question I haven't brought up before, but which doesn't affect me. If you use electric heat in EV, doesn't this system waste a huge amount of heat, maybe half, in engine compartment loss? That hot water you're making has to circulate at least a little by natural convection through the radiator, has to heat up the engine block which then loses heat to the surrounding air, etc. It seems like a terrible way to utilize electric heat compared to an inline electric coil in the hvac system.

There's a valve to keep the electrically heated water in a smaller loop when the ICE is not running.

 

[Atkinson]

This reminds me of an interesting question I haven't brought up before, but which doesn't affect me. If you use electric heat in EV, doesn't this system waste a huge amount of heat, maybe half, in engine compartment loss? That hot water you're making has to circulate at least a little by natural convection through the radiator, has to heat up the engine block which then loses heat to the surrounding air, etc. It seems like a terrible way to utilize electric heat compared to an inline electric coil in the hvac system.

If the engine is cold and you are in EV mode with heat on, there is a valve that isolates the heater loop from the engine to minimize losses.
What does happen in cold weather in HV mode is the electric heater is used to reheat the engine coolant each start cycle to minimize cold run time.
That constant on/off cycling costs gas generated electric energy in cold weather.
Would have been nice to use an exhaust heat exchanger and grill shutters for heat recovery like GM did for the Malibu Hybrid (but not the Volt) or like Honda did for the Accord Hybrid (but not the Clarity).
That would really help even in cool weather, but especially in cold.
Same powertrains, different expense parameters.
Apparently, they are not going to give you a big battery AND the efficiency goodies.

 

[Atkinson]

Insightman beat me by 5 minutes!

 

[insightman]

Insightman beat me by 5 minutes!

But you had more information.

 

[Landshark]

you are averaging 60 mph- EV best for slower driving

Yes, I averaged about 60 mph on the segment where the observations were made.

Yes, at slower speeds, or stop and go traffic, the car will go a greater distance on battery power. I’ve exceeded 65 miles on batteries in heavy traffic. I have variable distance round trip commutes. Typically, they are 40-50 miles, but could be 20 or 120. On the 40-50 mile days I operate in EV regardless of whatever speed the road conditions allow. Generally I keep it around 65 mph while on the freeway. Almost always the trip is completed on batteries. That’s one reason I opted for a Clarity over a Prius Prime. For me, EV is just as good for fast driving as it is for slow driving. Put another way, EV is optimal whenever I can utilize it to the fullest. I wouldn’t use EV for 10 miles of slower driving and HV for 30 miles of faster driving, when I can make the entire trip in EV.

What I did was simply a test, on a segment of a trip I have done repeatedly without using cabin heat. I made one run with the heat on and compared that to the other trips.

 

[Landshark]

If you use electric heat in EV, doesn't this system waste a huge amount of heat, maybe half, in engine compartment loss? That hot water you're making has to circulate at least a little by natural convection through the radiator, has to heat up the engine block which then loses heat to the surrounding air, etc. It seems like a terrible way to utilize electric heat compared to an inline electric coil in the hvac system.

As the diagram shows, there is a valve that isolates the coolant in the cabin heating loop from the coolant in the engine. How much coolant is in that loop if there is only 1.3 gallons in the entire system? It can’t take too much energy to heat up such a small amount of fluid, and even less to maintain that temperature. While small, there is some advantage to a bit of thermal mass.

That thermal mass may allow the heating element to have a shorter duty cycle than a pure electric heating element, such as what is in the heated seats. Those are either at 3-2-1 or off. The temperature sensor in the loop would control the duty cycle.

Another thought. When I conducted the test the car was in ECO mode, which affects the climate settings to conserve battery capacity.

 

[turtleturtle]

I wonder if OP is going to come back.

There’s a whole cadre of us angry, err… helpful, internet folks that need closure.

 

[coutinpe]

I have to say that the reason to drive EV is a lot more than saving money. Driving is serene. HV driving of this car is really only for the highway.

Absolutely agree.

Yes, I averaged about 60 mph on the segment where the observations were made.

Yes, at slower speeds, or stop and go traffic, the car will go a greater distance on battery power. I’ve exceeded 65 miles on batteries in heavy traffic. I have variable distance round trip commutes. Typically, they are 40-50 miles, but could be 20 or 120. On the 40-50 mile days I operate in EV regardless of whatever speed the road conditions allow. Generally I keep it around 65 mph while on the freeway. Almost always the trip is completed on batteries. That’s one reason I opted for a Clarity over a Prius Prime. For me, EV is just as good for fast driving as it is for slow driving. Put another way, EV is optimal whenever I can utilize it to the fullest. I wouldn’t use EV for 10 miles of slower driving and HV for 30 miles of faster driving, when I can make the entire trip in EV.

What I did was simply a test, on a segment of a trip I have done repeatedly without using cabin heat. I made one run with the heat on and compared that to the other trips.

I just moved from LA to Vegas a couple of weeks ago and my EV range jumped up 13 miles, from 52 to 65 in a few days, and it seems it goes up a mile per day. Just driving slowly on unknown territory plus way less hills here.

 

[David Towle]

If the engine is cold and you are in EV mode with heat on, there is a valve that isolates the heater loop from the engine to minimize losses.
What does happen in cold weather in HV mode is the electric heater is used to reheat the engine coolant each start cycle to minimize cold run time.
That constant on/off cycling costs gas generated electric energy in cold weather.
Would have been nice to use an exhaust heat exchanger and grill shutters for heat recovery like GM did for the Malibu Hybrid (but not the Volt) or like Honda did for the Accord Hybrid (but not the Clarity).
That would really help even in cool weather, but especially in cold.
Same powertrains, different expense parameters.
Apparently, they are not going to give you a big battery AND the efficiency goodies.

OK thanks gentlemen. Still some losses by conduction, but Honda probably weighed that against the likely longer life of a water tempered heater and the engine heating issue versus a simple inline coil in the HVAC. I probably would have gone the other way and just made sure the coil was replaceable with minimal work. Certainly would have cost less.

 

[David Towle]

But you had more information.

But you had a diagram.

 

[Landshark]

I just moved from LA to Vegas a couple of weeks ago and my EV range jumped up 13 miles, from 52 to 65 in a few days, and it seems it goes up a mile per day.

What happens in Vegas, stays in Vegas.

 

[JCA]

OK thanks gentlemen. Still some losses by conduction, but Honda probably weighed that against the likely longer life of a water tempered heater and the engine heating issue versus a simple inline coil in the HVAC. I probably would have gone the other way and just made sure the coil was replaceable with minimal work. Certainly would have cost less.

If parts of the heating system are shared with e.g. the Accord Hybrid, there might not have been room to put a heating coil directly inline. Or having a liquid coil might be more compatible with the BEV that I believe does have a heat pump. There may be safety or long term reliability benefits in keeping the high current electric coil away from the airflow too.

Hydronic heating is pretty common in home settings -- the house I grew up in and my parents' current house in New England have an oil burner heating water that circulates through baseboard convectors throughout the home. And I had an apartment in CA where the heating system circulated hot water out of the water heater, through a coil in the furnace blower, and back to the water heater. That worked okay for limited heating needs, but you could run out of hot water when showering if the heat was on!