Why is winter *highway* mpg so low?

[sapperforward]

Are you doing a lot of idling or warming up before driving? I didn't, I opened my garage and started driving. Even so, that shouldn't impact a 180 mile drive appreciably.

Yes actually I am and I didn't think about that thanks for pointing that out

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[MavMeister25]

Isn't the engine running 100% of the time at 75 mph? I use almost zero electric miles on my 75 mph 180 mile highway drives. I set cruise control to 75 and it just cruises.

I'm comparing summer 75 mph, 180 miles to winter 75 mph, 180 mile drive here. Summer is 35-36 and winter is 26-27.

Just crazy it impacts it that much. That's a 25%-30% drop in fuel efficiency for the same route, same speed, just different temperature. I've not seen that in our Prius.

Found this chart on a Canadian government website, most vehicles show a 7%-12% decline in efficiency:

Excellent post. I appreciate when people use specifics and clarify terms instead of throwing out generalities.

 

[The Real Maverick]

Just look at your information on your dashboard after a winter drive compared to a summer drive. My hybrid during the summer would run on electric for about a third of the miles. During this winter of very cold weather, I've dropped from 33% electric to about 10% electric. Driving at 75 mph also uses more fuel than driving at 50 mph. Most of this is caused by the heating of the cab, and all the extra heating that is draining the battery. The colder air moving through the radiator causes your engine to have to run more to keep the water warm enough to keep you comfy in your cab. It will get much better in the warmer weather, just like it does for all internal combustion vehicles.

For the fourth time.... "heating" does not drain the battery.... and like OP stated, once up to highway speed, there is waste heat available. At least in positive F number temperatures there is.

Short answer: a bunch of little factors mentioned are all working against MPG.

 

[The Real Maverick]

Isn't the engine running 100% of the time at 75 mph? I use almost zero electric miles on my 75 mph 180 mile highway drives. I set cruise control to 75 and it just cruises.

I'm comparing summer 75 mph, 180 miles to winter 75 mph, 180 mile drive here. Summer is 35-36 and winter is 26-27.

Just crazy it impacts it that much. That's a 25%-30% drop in fuel efficiency for the same route, same speed, just different temperature. I've not seen that in our Prius.

Found this chart on a Canadian government website, most vehicles show a 7%-12% decline in efficiency:

I don't know where you learned to read charts. But looks like 20% drop
In general, to me.

 

[Whitty1]

I have a '23 hybrid, and drive a normal highway route of 180 miles @ 70-75 mpg. My average speed is around 74.

Did it today, first time in cold temps (28°F weather) and got 27 mpg. Normal is 35-36 over the summer months. Keep in mind tire pressure was ~40 on all four (just filled them prior to trip).

Curious why low temps effect the hybrid mpg so much? Heat being on shouldn't bring it down from where it is in the summer, as the engine is running 100% of the time at ~75 mph.

I took my 24 Lariat with 1300 miles on it for a short road trip yesterday to see how it would do. It clocked 36 MPG one way and a little over 43 on the way back in 50 degree weather on a sunny day.

 

[hj630]

We actually did a study on this during my graduate class for my engineering PhD degree. Several factors,
1. the Atkinson cycle efficiency is directly related to ambient temp and engine temp. When ambient temp goes down, it reduces efficiency.
2. Wind tends to be stronger in winter. And drag is proportionate to v^2. so even slight increase, will increase drag a lot on highway
3. Your engine will stay in ICE mode longer when starting up to heat up. For shorter trips, you will see big drops on MPG too.

 

[Master Blaster]

I took my 24 Lariat with 1300 miles on it for a short road trip yesterday to see how it would do. It clocked 36 MPG one way and a little over 43 on the way back in 50 degree weather on a sunny day.

Clearly you were either fighting a strong wind on the way there, or its at a much higher elevation than where you started from. Also unknown is at what speed? Aerodynamic drag is proportional to the square of the speed, so there is a huge increase in losses between going 60 and going 75.

 

[Whitty1]

Clearly you were either fighting a strong wind on the way there, or its at a much higher elevation than where you started from. Also unknown is at what speed? Aerodynamic drag is proportional to the square of the speed, so there is a huge increase in losses between going 60 and going 75.

I set the cruise at 5 MPG over the speed limit (70). It was from Gastonia NC to Spartanburg SC and back. I was showing 14 electric miles when I got back out of 74 miles. I didn't pay attention to the electric miles going. It probably was more downhill coming back

 

[HeyBales]

On highway the engine runs 100% of the time, which is why I wrote *highway* in my title. Should be zero factor.

Zero factor on highway going 70-75 on flat terrain, you don't use the battery, you use the ICE for sustained highway driving.

Only initially on startup not hours into the trip, I drove 2:40. Should only have been a factor in the first 5-10 minutes.

No, A/C is off and humidity is very low right now, so should not be running much. I use Auto on low fan setting set to 72°. I did try turning heat off but that did not appreciably change the mpg.

I'll add to your excellent points that your premise as explained were missed by many.

The AC being powered from the HiCurrent side (HVB if engine not on), and with engine running on the highway, that is getting plenty of power so it really doesn't matter when defrost uses it.

Frankly even others commenting on AC - your engines are likely to be running anyway in the cold for the other factors mentioned - therefore the AC won't be having an effect on mileage as the HVB wasn't going to be used anyway.

 

[HeyBales]

I've always kept track of fillup trip mileage for over 30 years, as sometimes it's an indication of something about to go bad.
Now it used to be just on the receipt, after noting the trip and total miles, I'd note the MPG.
When putting that receipt in my car envelope (yep tracked yearly for insurance miles in case I could fall into lower category for cheaper insurance), I'd compare it to prior fillups just at a glance.
Several winter camping trips south to Ozarks (tailwind down, headwind back usually), and 1 summer trip somewhere, allowed highway only compares.
Always lower in winter.

The impact on the Maverick mainly city driving MPG's was shocking at first, because on prior cars I was never able to watch instant or trip MPG until fillup, which still takes a while but not monthly for now (barely 600 to 400 miles/fillup).
But I knew it had to be worse so once I got over the bummer, I know now why the estimated MPG avg annual figures are what they are.

Appreciate the post above about Atkinson being less efficient in cold anyway. (now I really want to find 4 fins to install in the shutter missing spots)

 

[Block]

If this is a sample size of one trip that's not valid. You may have been driving into a wind.

 

[Block]

I watch my gas mileage closely on my 2013 Ford Focus non turbo.. I average upper 30s in summer 33 to 35 in winter in Syracuse New York... Around 10% maybe 15% but not 20% lower... I'm using the same tires year round and I keep them inflated a couple pounds above recommended.

 

[Optimus]

Lots of good information has been presented already for lower MPG in winter. I concur, and it is NOT a Maverick problem, a hybrid, problem, or a Ford problem. Gas automobile engines suffer from lower MPG in cold winter temps. Engines are designed to run most efficiently at operating temperature. The cold weather robs an engine's ability to get there, be it the radiator robbing heat, the HVAC cabin heater, and yes even electric heated seats, steering wheel, windshield, and mirrors (because the gas motor has to run to charge the battery to power these devices). I consistently and predictably get about 20% less mpg in any vehicle in the winter.

If it's -20F outside, I can expect 31-32mpg for our average. IF it's +25F above zero, then we see closer to 35-36F in winter. Summertime, with temps ranging from 60's to 80's, we are consistently 46-47mpg. This same thing has happened with our other vehicles too, hybrid or not. Yes, dropping from 47 to 31 sounds a bit harsh, but try dropping from 16mpg to 12mpg! Do the math.... A 20-30% drop when you're mpg starts super low like 16 is much harsher cost-wise than when it starts at 47mpg and drops to 31.

 

[flashfearless]

It's cold. You're running the heater. You are speeding. And you are running up to 10% ethynol. My winter mpg is like 33-35. Spring / Summer is solid 45.

 

[Stillman]

I have a '23 hybrid, and drive a normal highway route of 180 miles @ 70-75 mpg. My average speed is around 74.

Did it today, first time in cold temps (28°F weather) and got 27 mpg. Normal is 35-36 over the summer months. Keep in mind tire pressure was ~40 on all four (just filled them prior to trip).

Curious why low temps effect the hybrid mpg so much? Heat being on shouldn't bring it down from where it is in the summer, as the engine is running 100% of the time at ~75 mph.

It's lower in any car in the cold.

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