Second the block heater. worth 2 mpg below 60 deg F on shorter trips

I also have been seeing a serious drop in FE on the highway. But my in town mileage is about the same. IMHO i think it has to do with the cold air induction and the extra cooling of the radiator constantly keeping the engine cooler than optimum.

 

I agree with Laurie that even taking 5mph off your typical speed should give you a measureable improvement in FE.

Actually, I dont usually display my trip FE gage much while on my trip - usually only when arriving. I dont get distracted/frustrated watching it.

I too, have much lower FE during cold months - down in the mid 40s now versus above 60 in the summer. I was frustrated by it but seems that much of this is temperature related - here are my 30 tanks FE versus Temps:

Regression Analysis: mpg (US) versus °F
The regression equation is
mpg (US) = 40.89 + 0.2482 °F

S = 2.57306 R-Sq = 71.4% R-Sq(adj) = 70.4%

Analysis of Variance
Source DF SS MS F P
Regression 1 478.541 478.541 72.28 0.000
Error 29 191.999 6.621
Total 30 670.540

So at 20F (today), I would expect 40.9 + 20 x 0.248 = 46mpg (which is what I am getting). At least for my HCH2 and trip, every 10F drop in temp costs me 2-3mpg.

 

Thanks to everyone for the tips (block off radiator, use an engine block heater). I have read about both of those options on other postings. I might add that my poor fuel economy experience happened on a trip from AL to MI on I-65 in early December and then back to AL this past Wednesday & Thursday. Now that I'm back in AL where it's warmer and I'll be driving more slowly (45 to 55 MPH) on the back roads here I'm hopeful that my fuel economy figures will rebound into the mid 30s.

 

Wow - you're a rarity. I don't think I've ever run into anyone (check that, any non-hybrid driver) that keeps that detailed of records on their mileage. Kudos to you!

Then obviously you probably would know better than anyone if there is a difference in the cold weather hit of hybrids vs non-hybrid vehicles.

 

Its all about THE NUMBER

 

Temperature was in the mid to upper 20's today (no wind) during my trip to a new ski area 90 miles away. First I filled up with E90. My scangauge was hanging between 30-31 mpg driving 55-60 mph on two lane and four lane state highways.

I have a complete upper grille block and use a 16 inch long (1/8 plywood) lower grille block that leaves a small opening at each end.

 

None of the current crop of hybrid vehicles are designed to be especially fuel efficient at hwy speeds, hwy cruising. Think about it, if there is little opportunity, or no opportunity, to use regenerative braking to recharge the hybrid battery then you are just like a non-hybrid car out there on the roadbed, but with a slight detriment to FE over them.

Because of the hybrid design, derated ICE, battery Boost, use of the hybrid battery cannot be avoided. And what resource do you have to recharge that battery...the derated ICE, of course.

An additional factor during the winter months may be that the FEH/MMH will substantially reduce the level of regenerative braking available for recharging the battery should the OAT decline below freezing.

 

Hmm, I still think that hybrids tend to be the MOST efficient, if not "especially" efficient vehicles in their respective classes - even in the cold and even at highway speeds.

Seems that EV boost/regen will tend to work, even on slight upgrades/downgrades - once the vehicle is warmed up.

Although I am only getting 45-50mpg at 55-60mph in freezing temps - I dont think there are many vehicles out there that would do as well. Maybe a non hybrid 1.3L Civic would do as well.

Yep, seeing your FE drop 10-20mpg can be frustrating but thats OK. My 96 Jeep XJ got 17mpg year round - it sucked all the time....

 

What do you mean by "derated ICE"???

Do you mean to imply "underpowered"?
Surly you didn't mean this.

Cruising on flat ground, the FEH requires 22 HP @ 55 MPH.
33 HP @ 65 MPH and 44 HP @ 75 MPH.

Going up the steepest parts of the Colorado Rockies ( 7% grade sustained for like 12 miles ) with 500 pounds of cargo, my FEH ICE was making 50 HP to keep me moving 60 MPH up that 7% grade. I needed 75-80 HP to pass slow semis on the upgrade at about 65 MPH.

This car has a 134 HP ICE.

Surely the only logical arguement is this engine is overpowered.
ICE's are most efficient under heavy load.
-John

 

I'm being picky on this statement. The statement "if there is little opportunity or no opportunity, to use regenerative braking to recharge the hybrid battery".

During highway travel, my Ford Escape Hybrid does not display a slowly degenerating hybrid battery state of charge. This vehicle is designed to maintain hybrid battery state of charge in more than one way. I will let the well known posters accurately describe this.

As for the cold weather effect on highway mileage. Yesterday I averaged 30 mpg (almost 200 miles) on E90 and today I got 32.1 for 210 miles on straight gasoline. Yesterday's temperature was in the mid to upper 20's and today was in the low 30's. Both days involved speeds between 50-60 mph on two and four lane highways. Mileage is less than what I experienced last summer but not the 18% drop others are reporting.