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

What type of driving, all highway or mix? Heavy use of heat and/or defrost? Regardless I'd say you have some type of issue IMO.

I live in CT also. I've only measured mpg when on a road trip to Ohio and back and when I did it was at/above the rating. IIRC was closer to 42-45.

 

Really sorry to hear it. If charging is expensive, are there any free chargers near you? Volta at the grocery store? This is a great way to boost your range and mileage by plugging in when you go out for shopping. Car performs at its best when it starts with a charge.

 

Also all the standard things. Checking the engine air filter, tire pressure, recent oil change, and unburned transmission fluid.

 

There are a lot of “distractors” in the OP’s post.

First, disregard anything the displays tell you about range or miles remaining or gas mileage or anything else.

Then just run on HV all the time through several tanks of gas. Let the nozzle decide when to stop filling - don’t attempt to “top off”. Divide miles traveled by gallons used. Simple.

If, after that, your real life mileage is as reported, something may very well be wrong. From numerous trips in HV mode, I’ve always seen between 35 to 45 mpg. If you’re not seeing numbers in that range, it’s time for a trip to the dealer.

 

I find the heater dramatically affects my mpg. I am in upstate New York. Running outside air, with high inside temperature is hard on mpg. I often see real mpg below 35 in winter. (I like to be comfortable, so I run the heater.)

It acts like the engine has to generate electricity to run the electric heater. Maybe there is something wrong with my car, but it has acted this way since it was new.

 

@ClarityBill , my experience is limited since I live in Alabama, but I have easily seen several miles per gallon hit when running the heater and operating in HV mode. Probably easily as much as 5 mpg hit in cold weather driving (around 30 degrees F).

 

The gas mileage issue is likely due the short driving trips. One hundred miles divided by 7 is around 14 miles a day round trip.

Some areas of the country electricity cost makes driving a gas car cheaper. How much does he pay for electricity per kw/h?

 

I seem to get amazingly good mpg if I start with a fully-charged battery and run in HV mode on the interstate.

 

Is there a baseline mpg for this car?
Bought in Oct, presumably charged and drove in EV for a month or two, then in Nov or Dec started driving in HV.

Starting a trip in HV, the engine will need to warm up for a few minutes. During that time the car will be using primarily battery power. Once the engine is warm it will work to bring the battery SOC back up to the original set point as well as send some electricity to the motor. On a short trip the engine could spend most of the time warming up and recharging the battery. This is not an efficient procedure.

Despite the horrendous fuel efficiency, which actually works out to 18-23mpg, if you are indeed using 5 gallons every 90-115 miles, it may be cost effective at $2.70/gallon or $54/mo, compared to $70/mo for electricity.

Are you metering electricity for recharging the car separately or could there be other electricity consuming devices at play?

 

The 40 mpg highway is the yearly average. You get better in the summer when it is warmer and worse in the winter when it is colder and you are heating the interior of the car. We typically get 45 mpg (70 mph) highway summer and 30-35 winter in Michigan.

 

This.

Ignore the display. The fuel tank has about a gallon left after it reads zero.
Go through several tanks like the person above stated and let the pump shut off. Then figure out the mileage.

Also check with your utility, they might have a EV rate. Which utility is it?

 

That's my point. His dad is driving short trips.

Instead of driving 7 miles one way, try driving 20 miles one way and tell us what the mpg is calculating to be.

It seems to me, that his dad is getting hammered twice: once because the gas engine isn't efficient at doing short trips and two because the cost of electricity is high where he lives.

 

Robert_AlabamaWell-Known Member
New@ClarityBill , my experience is limited since I live in Alabama, but I have easily seen several miles per gallon hit when running the heater and operating in HV mode. Probably easily as much as 5 mpg hit in cold weather driving (around 30 degrees F)

Yes, because you don't get as much regen and it all goes to heating. The heating does not effect the gas milage but does effect the EV milage and you are not getting the full results of the hydbid.

 

I can't provide any numerical evidence, but my instinct is that HV mode greatly reduces the use of electrical energy for heating because once the engine warms up cabin heat comes mostly from the engine waste heat. Perhaps this doesn't reduce the electrical impact to zero (although it's possible that it does). Of course, you need time for the engine to warm up so short little trips will have a greater electrical impact than longer ones.

 

It can get rather cold here in E TN. My habit on cold days is to start out in HV mode for 2 or 3 miles, letting the engine warm up so as to let the engine heat warm up the car initially. I then switch to EV mode for the rest of the trip.

Probably makes very little difference, but it seems more efficient to use engine heat as opposed to electric heat for initially warming up the cabin.

 

Most probably your engine runs in generator mode. The 40-45 mpg is mostly for highway, where the engine drives the wheels mechanically (direct drive mode). The direct drive mode is very efficient because power directly goes from engine to a single speed transmission (reduction gear) and to the front wheels. I have seen 40+ mpg in high speed extended (600 mile) highway driving.

If your driving condition doesn't allow direct drive to be engaged (e.g. city driving), your car will work in series hybrid or range extender mode (like a BMW i3 REX). This mode is much less efficient because the mechanical energy converted to electrical in the generator and back to mechanical in the motor. As a comparison the BMW i3 REX gets 30-35 mpg when running on gas, therefore a heavier Clarity with more complex drivetrain could get less than 30 mpg.

 

Some quick math with one assumption. Let’s say that your winter EV range is 28-30 miles on a full charge. The car would be getting 2 miles per kWh. 400 miles per month would require 200kWh’s. $70 for 200kWh’s equals $.35/kWh.

Are you/your dad paying $.35/kWh for electricity?

 

As others have noted, don't use the car's MPG or remaining range estimates for any of the calculations; they simply aren't accurate enough for this purpose.

Knowing the driving pattern would help a lot -- 100 miles as a once a week drive to a place 50 miles away (and back) is going to be *very* different from 4 drives of 3.5 miles each every day with the car cooling off between. Short trips in very cold weather with heavy heat and defrost use will cost MPG and EV range substantially. And potentially by a greater percentage than in an ICE vehicle, because the Clarity is firing up the costly electric heater (using battery or motor generated power) right away when the engine is cold (where the ICE vehicle simply isn't getting heat then), only switching to the engine's heat when it warms up, which for a 3-4 mile trip is not going to be until you get where you're going.

You could do some experiments on a nicer day where you can turn off the heat (set the temp controls to Lo, defrosters off, make sure the AC control on the climate screen is off), and I bet you'll find both the EV range on a charge and the MPG in HV are much higher. But for HV experiments you really need to fill the tank in a consistent fashion and measure the miles between fills divided by the second fill's gallons. For EV experiments, use Econ mode (or be careful not to trigger the engine) and drive until the EV range reads 0.0 and the engine comes on; the number of miles you drove divided by ~14kWh is the Miles per kWh.

FWIW in both Clarities I've had (2019 and 2020) HV highway mileage was 43-45, but that's with just a few road trips to measure. I've never used HV around town for long enough to measure.

 

I fear we are wasting our energy here.
The OP stirred up quite a number of constructive comments, but now is MIA.

This sort of a post is frustrating.
It is clear that the OP did not provide concise enough information to resolve this, but has not participated in the discussion.
The bottom line is that Clarity users do NOT experience 25-28 MPG under any circumstances.
It is likely that his 'measurement' is suspect, rather than having something wrong with the vehicle.