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

Anecdote:

We had driven our Ford Flex to Rockford IL to pick up a 21’ travel trailer. We normally got about 22-24 mpg on the highway, but knew we’d take a hit while towing. But our first leg southbound towards home, our car’s display was showing mpg in the 8’s. OUCH! At that rate, you can almost see the needle on the fuel gauge dropping as you watch it! Anyway, we figured out we had been driving into southerly winds gusting 20 to 30 mph. Under normal conditions we see 11 or 12 mpg, which seems to be about average for a trailer that size.

So yes, wind definitely makes a difference!

The setup in question...

 

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.

 

When I precondition my Clarity Electric with a fully charged battery, it draws 7.2 kW from the EVSE. Not apples to apples since it is using a heat pump (more efficient than resistance heating at least in the long term). Part of the heat pump operation is lots of fan noise under the hood, and fans draw a lot more power than most people realize. If the heat is on while in a parking lot, the fans drown out the pedestrian alert.
Someone with a phev and an EVSE that measures power usage could try the same and get an idea what the heater will pull.

 

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.

 

Well, the 75 mph wind was rather a rhetoric figure for a wind strong as hell, since I wasn't carrying an anemometer, but as you described, running against the wind requires an energy proportional to the force that would send a sail ship running over the waves in the opposite direction. Now I wish some smart guy would come with a device using this huge eolic force to recharge the battery...

 

They’re too busy trying to figure out how to tow a Tesla behind a motorhome and charge the battery.

 

What is the weight of that trailer?

The best trick to avoid a significant loss of mileage in head or crosswinds is to drive a 16 ton diesel motorhome. The mileage only drops from 8.5 to 7.5.

 

Rivians can be tow charged, and they did it with a prototype in Long Way Up:

 

Of course. That’s genius.

Imagine towing it with a Cybertruck, the Rivian could charge the Tesla for all eternity. They must have some other practical applications in mind as well.

Rivian is a step ahead of Tesla on this, but I’m downgrading them a notch on the Smart Guy rating for promoting this feature as useful.

 

Empty/dry spec is 3,499 lbs. Max weight 5,000 lbs.

 

Flat towing a Rivian behind a motorhome and implementing regen when braking is "free" energy that otherwise would be lost by using friction brakes.

 

This would certainly explain why it takes so long for the inside fan to start blowing when the heat is turned on. Waiting for the coolant to warm up.

 

I was referring to the concept of “tow charging” that you mentioned. My interpretation of that is, towing the EV specifically to charge the battery. It looks like they are towing the Rivian with a diesel semi tractor. That can’t be an efficient way to charge the vehicle.

I did read a review of the first 3 episodes of the show. Rivian installed 140, Level 2 charging stations along the route. They also devised a Vehicle to Motorcycle charging system. Perhaps they drained the Rivian battery while charging the motorcycles and needed to drag charge it to the next station?

Supplemental braking systems on a vehicle that is towed behind a motorhome, apply the brake pedal in the car by various means. Ours has a sensor that requires a certain amount of inertia from decelerating. It also must receive a signal that the brakes in the coach are being applied. When I utilize the Jacobs brake, the coach will slow without applying the brake pedal. In slow or stop and go traffic there is not a sufficient amount of inertia to trigger the system, even when applying the brake pedal. In those cases there would be no regenerative energy created. We also travel with a full tank in the towed vehicle as it is an “escape” option if we have a mechanical issue. So, if I towed an EV, the battery would always be fully charged prior to departure.

And it wouldn’t be “free” either, because the kinetic energy was created by the motorhome.

 

Is the Flex going to be your regular tow vehicle? I’ve seen a towing limit of 4500lbs on a property equipped Flex.

 

We’ve towed about 20,000 miles over the last 6 or 7 years to no ill effect. We did have the receiver on the Flex reinforced to accommodate tongue weight over that recommended by Ford. Can Am RV in London, Ontario did it for us. Here’s their take on a Flex’s abilities as a tow vehicle.

https://www.canamrv.ca/blog/post/hitch-hints-defined-style-434/

 

To your knowledge, are you operating in excess of any of the manufacturer’s specified maximum capacities?

Towing?
Tongue weight?
GVWR?
GCWR?

 

Without researching again, two I’m sure of.

When putting the combo together Ford said 450 lb Max tongue weight. LivinLite said 440 lb tongue weight on our model. Problem was, that must have been without battery or propane or normal loading. When we measured ours loaded it was 620 lbs! The Can Am mod tied the receiver, which had been supported by just the unibody, to the rear suspension.

Towing capacity is listed at 4,500 lbs, which we’re right up against when loaded normally.

But I apologize for the hijack - my anecdote was just to support the drastic effect wind can have on gas mileage.

 

620lbs would be just a touch high if you’re at the 5,000 GVWR. 10-12% of actual weight is ideal. RV manufacturers tend to publish the lightest weights and then tell buyers they can tow anything with their current vehicle. The 440lb they gave you is about 12% of the dry weight. The only way to know for sure is to hit the scales. If you’re confident that the trailer is around 4500lbs, the tongue weight should be ~500lbs. So maybe some heavy items need to be moved to the rear.

That 620lbs is mostly on the rear axle unless you’re using a WDH. It is also part of the Occupant and Cargo Carrying Capacity calculation for the tow vehicle. More folks than not, an estimated 60%, operate RV set ups that are overweight.

Until we hear from the OP again, we might as well chat about something.

 

WDH and sway control. Car rides level and handles well.



Here's the receiver reinforcement Can Am RV did for us:



As I said, before that the receiver was only supported by the unibody. The folks at Can Am said that looking at it even 450 lbs seemed optimistic.

Sounds good to me. We're likely staying with this setup at least until our Cybertruck gets delivered!

As an aside, I have no idea why my plain text is showing as links.

 

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 Long Way up charging was an option that was faster than the other choices available. The EnelX L2s installed were 32A, and there were 2 per location to charge 4 vehicles. This was further compounded by Harleys design/engineering choice to allow DCFC on the Livewire, but limit L2 charging to L1 speed (1.44 kW). They were traveling pretty much together and a production schedule so sitting all the vehicle for hours at the charging stations was not an option. The short tow behind the truck got them 10%+ charge and got them to the next stop. Using a Rivain as a brake while towing is something no other EV can currently do, and will hold some usefulness for people. Emma Hall drove a Rivian in the Rebelle rRally, and she was appreciative of 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? Nope. A useless feature that knocks them down a notch? Not in my opinion.