It was probably this way last winter too, but I didn't really start watching mileage that close until March or so. I also didn't have 2 SGII's hooked up last winter!

The part that's really bothering me is the RPM jumpiness up to 2400. I can usually coast or accellerate lightly, but jumping up to 2400 so easily is hurting me in town.

-- Rick

 

I notice there's almost no elec assist when this happens. Below 20° or so with the battery cold, it seems to derive more (if not all) propulsion from the Atkinson-style ICE. We know this design gives away low end torque in exchange for ~5% better efficiency. Under normal conditions, it's no big deal since torque comes by the truckload from the electric motor, more than offsetting the efficiency-biased ICE design.

On mine in cold temps it seems like the computer won't even try to power the vehicle with ICE alone at low revs, and tells it to rev to where its meager torque "lives" and stay in that range. It jumps right to about 2200 RPM.

Torque manifests as that push-in-the-back feeling. In our torquey hybrids we're used to pressing the pedal a little and getting that strong push. When that push goes away or is diminished, you really notice. I think the ICE revs in an effort to make up for the missing push.

I'm not a SG owner and I'd be curious what clues a SG would provide. I notice that mine does what others have seen and sometimes revs when I stop. In addition, shifting to 'L' results in some charging for the first couple of stops, then the needle moves back to the middle and the ICE revs up just as it does when the battery is full. Lastly, it almost always revs as I park in the garage at work on very cold mornings. Right before shutdown, it goes to about 1500-2000 RPM and the dash gauge moves to the "assist" side a little. Is it possible that it's spinning off power because the cold battery can't/won't be charged?

 

Terry, I think you made a good connection. The part about when the battery is cold and can't produce, you lose the low speed torque. Thus, the engine is running ~1000 RPM faster than we are used to at launch from stop lights. Very good point, and that may very well be the reason.

I'm not sure what you are saying in your last sentence.
If you are standing still, there is nothing to "spin off".

The battery gives and takes at low temperatures.
But the amps are about 20-25% as much as usual until things warm up.

 

You are so right about the battery give-&-take. It's predictable in warmer weather, but the cold changes things. It does appear that the 05-08 models do behave about the same in regards to battery management and EV mode in cold weather.

Everyone participating in this thread is interested in what makes these beasts behave the way they do. It's a challenge that I think we all enjoy

 

Here's some more detail:

In my old Prius, as well as in the FEH, I've seen conditions where the battery charge apparently was excessive and the vehicle tried to discharge by revving the engine. Usually it's after restarting when a long descent was followed by a shut down and a period of the vehicle sitting in the sun. Upon stopping at a red light or stop sign, the engine revs to about 1500 RPM and just sits there and the charge/assist needle moves over to the assist side, and the battery cooling fan comes on noticeably higher than normal. I've been told that this is the system's way of "spinning off" excess charge from the battery.

I can not see why the FEH would do this in cold weather. But that what it does occasionally after cold starting and driving short distances in really cold weather.

I've experienced this behavior under three conditions: A) Going down a long descent then parking in the sun, then restarting B) Twice when the FEH went through what I think is called "battery conditioning" and C) The last few mornings after driving about 4 miles in 5° to 15° weather. I drive 4 miles to work. The vehicle is just warmed up, the heater fan kicks on at about the 2 mile mark, then I park. Before key off, it revs to about 1500 RPM and just sits there, with the needle over on the assist side. Weird.

 

I think it is running 1500 RPM to create heat. ( for both engine, and battery )
I suspect it is really burning gas, and the needle move is slight, amps wise.

In the cold, while parked, I've watched my SOC go from 53% to 49% to 53% to 49% repeat, while just sitting there. This is the first winter I've had the enhanced SG, so I don't have a lot of data. I'm willing to bet in warm weather, once the car gets to 53%, it just stays there ( or pretty close ) the whole time you run the engine while parked.

Maybe someone in So Calif, Arizona, or Florida can tell us now what the car SOC does when you run the ICE in park for 10 minutes. Otherwise, I'll tell you in about 5 months! -John

 

I've noticed some slightly strange behavior, beyond what has already been mentioned in this thread, but from what I've read, it seems like it's normal.

The first just seems normal for any engine in sub-zero F weather. While driving at low speeds on a cold engine, I've noticed the engine seems to run a little rough, with the RPMs fluctuating slightly but still right around 2500 RPM. It's just enough to make the needle move visibly, about once every second, and you can feel it in the car as a slight acceleration. I've only noticed it when it's below 0F and it was -18F here on Thursday night. It seems to go away when the engine starts to warm up.

The second thing I've noticed is that the battery seems to constantly drain and recharge, according to the hybrid display. Even when driving at about 45 miles per hour when it should be running entirely on ICE power, it's either charging or assisting, yet the engine RPM's remain constant around 2500. Considering that the hybrid display only shows 40-60% SOC, I would estimate the swing is between 45 and 55%. Again, it only does this when it gets down into the single digits or colder and returns to normal when the engine warms up. That seems normal enough, but it seems backwards the way it's doing it. The battery may be assisting at a complete stop or while it's warming up and charging while trying to accelerate, causing the engine to rev up to around 4000 RPM to get just enough power to go.

 

My mechanic ran my engine in the shop for a total of 1 hour.
My tank MPG is down to 19.7.

Do I have to record this one in the GH database???

 

That reminds me of my first experience with a Hybrid. I drive an 06 now, but I had an 05 FEH originally.

I work at a car dealer & we took the 05 in trade. I had always wanted an Escape Hybrid (I have always loved SUV's but refused to drive one that got 12 mpg), so I bought it immediately.

When I first went out driving it, it was reading under 20 mpg & I remember thinking hell that's hardly any better than a V6 Escape!!!!

Later I found out that our doll-up department had shampooed the rug & left it running with the heat on for an hour & a half to dry the rug.......

~John