Mine is easier to get into EV. I need an initial 184F CHT to go EV. I have seen EV with CHT below this level and have seen FWT below 135. Cold spell here too. I should get my camera in the car and take a few photos.

 

I started up my FEH (inside my garage with the use of the engine block heater the previous 4 hours) at 8F, I had a TAV of 55F. After driving several miles my FWT rose above 152 and my CHT was 186 but I could not go into EV. A mile later, I noticed my TAV had risen to 57.6 and I slipped into EV despite my CHT only 186. After 8.5 hours of sitting outdoors in no warmer than 12F weather, my TAV was 36.4 and my SOC decreased to 33--I had backed out of the parking space as I usually do.

Does the trigger for EV also include a TAV of 57 and above? Will monitor in the next few days.

1-24-14 1F in am. Car was 55F tav at startup after long overnight session with the engine block heater. Drove to work, managed to obtain 188F CHT and 154 FWT and 57.2TAV but vehicle did not go into EV despite the trick of double brake tapping and shifting into and out of "L". Saw the tach move after moving the shift lever but..it refused to go EV. I'm assuming this due to the too cold TAV. Will report on 1-25-14 after a longer (20) mile drive.

1-25-14 20F outdoors with strong wind. FWT 156 CHT 188 TAV 60 and I go into EV. It is looking like the TAV must be around 59 or warmer for EV to occur.

1-25-14 later in the day 23F outdoors with strong winds, FWT 158 CHT 192 TAV 66 I go into EV. A few hours later with a shift of winds from the southwest to northwest brings dropping temperatures. 16F outdoors FWT 160, CHT 196 TAV 71, I can't get into EV. Braking down a long hill brings the SOC to 66.7 but still no EV at the bottom despite other parameters meeting EV requirements. It appears 20F outdoor temperature might the tripping point for allowing EV. I don't remember this as a trigger in the past and does this also relate to vehicles having more than 100,000 miles on them? More evidence that regenerative braking does not disappear when the outdoor temperature is 32F or below. Might be wise to plug in your FEH engine block heater immediately after work--if it has been sitting all day outdoors in cold winter weather--in an attempt to bring up its temperature and to improve those mpg.

 

With temps more reasonable today (near freezing), my FEH is acting perfectly normal. So it appears there is another set of parameters when it's really cold (near zero F) out. I can live with that. At least it appears nothing is broken, thank goodness.

 

I did it! Got photos of my vehicle going into EV with the temperature below 10F. An important key is that the hybrid battery temperature must be 60F or greater. Once TAV hits 70F, the frequency of EV greatly increases.

 

Yeah, I can get mine into EV mode even below zero F once it is thoroughly warmed up. It (EV mode) is just relatively short lived.

EDIT ---
Yesterday it was 'stupid cold' here with a high of around 10 below zero F. Starting with an average battery temp (Tav) of 19, once it got to 32 my FEH would drop into EV at stop lights. It took until it was above 50 (Tav) before I got any useful acceleration from a light in EV. Overall I'm still getting above 20 MPG in this 'stupid cold' weather which is way better than the 12 MPG my T&C van would get.

 

Wouldn't those wires interfere with the passenger air bag deploying? On the 2008 and later it comes straight out of the area above the glove box, not sure about the earlier models.

 

A long time ago I posted an actual graph of HV battery output in Amps vs. battery temperature. I have long ago proven that it is the battery temperature that matters, not outside air temperature.

I don't have that graph handy. But GENERALLY SPEAKING the maximum output of the battery is around 78 amps. The allowed draw on the battery decreases about one amp per degree F ABOVE 95 ( only tested to 109F ).

Going down, you loose one amp of battery output per degree F below 72F.
(going by memory, dont count this as exactly correct)

So by the time you get to 20F you only get about 20 amps.
At zero, you get hardly anything (allowed) but obviously there is enough amperage to start the car.

In brief, yes the rules change in frigid weather. Engine shut off at stoplights is possible at zero. but if the battery is cold, there are not enough amps available for EV driving.

 

Since reverse is electric only, would the power available for backing up be reduced in cold weather?

 

I haven't noticed any effect from the cold with reverse, even at sub-zero F temps.

 

The power for reverse can come from the battery, or from the gas engine generating power spinning the generator to go in reverse.

So in really cold conditions, the engine will run at high RPM to make electrical power to move the car in reverse. This power is up to 50 horsepower, more than plenty for backing up.
John

Remember your FEH has 3 power plants:

133 hp gasoline engine
94 hp traction motor (becomes generator when braking)
50 hp generator (becomes a motor for starting)

With the battery and generator on the same grid per se, either one can power the traction motor to spin the wheels. In fact, since the engine, traction motor, and generator are on the same plenetary gear set, any of the three can move the wheels too. But the engine can't spin in reverse. And there is no reverse gear.