We've had our 2006 FEH 4x4 for about 18 months, meaning we took it through a NE Ohio non-typical mild winter last year. However, with this winter's early harsh, cold blasts, we've seen a significant reduction in mileage, both per-tank and per trip, that seems to be tied to the weather (from a typical 29-31 down to, currently 21.9). As well, we've experienced a rather odd phenomenon: On cold start, the ICE has been "revving" far more than typical for its little self, and in odd ways. While the transmission is a CVT, at lower speeds (sub-40), the RPM's stay high, even when the engine is not under load, almost the same feeling one would get in a typical automatic transmission where the car is "hanging up" in second. Once beyond 40 mph or on the highway, it returns to a relatively normal state.
We took it to the local Ford dealer suggesting that it might be either a faulty IAC valve that needed cleaned or replaced, as no trouble codes of any kind came up, other than the odd RPM issues. The dealer came back with a suggestion that the entire throttle body needed replacing to the tune of almost $800 ($493 for the part alone). A little research suggests to us that the throttle body is likely not the issue, and we've not returned to that dealer.
Add this: When it's doing what it's doing, putting the can in neutral or part and attempting to "rev" the ICE gets virtually no response; however, the ICE responds normally to the same action when going down the road.
When its really cold out, the amount of power that the computer allows to go in/out of the battery is limited. The colder the battery gets, the more you will notice stuff like that. One morning I started my FEH it was about 5F outside and I had NO electric assist until the battery pack warmed up. Reduced mileage in cold weather is normal in the FEH, especially if you take short trips. One thing that does help is if you're driving in city traffic wear a heavy coat and don't turn on the heat. The more heat you pull off the motor, the longer the computer will run the engine. I generally don't run my heat at all unless I'm on the highway and there's no chance of it shutting off anyway.
EDIT: One thing I forgot to mention. The day I had no electric assist, it was revving at 3.000 RPM to go 25 MPH.
Much thanks for the tips. We have heated front seats, so is it a good trade to skip the cabin heat and just stick with the bunwarmers? And thanks for the reply, too. Your Beast reminds me of our gone but not forgotten 1996 Suburban K1500 4x4, the Green Monster. Went off to work on a farm at 307,000+ miles with the original Vortec 5.7, with no rebuild, under the hood, and a lifetime average mpg close to 17.5 mpg.
Yeah, my average on the K1500 is low because I used it as a daily driver in the city for years. It just keeps on going though. If I covered the odometer on mine and let you drive it, you would never guess it has nearly 200,000 miles on it.
I don't have heated seats in the FEH, but I would use them before I used the cabin heat. I usually don't turn on the heater until the engine is warmed up, and then I turn it back off at stoplights so it doesn't force the engine to restart.
Our Suburban was just the same - drove just as tight as the day we brought it home and everything just held up and kept working and working. We just didn't have soccer teams and scouts and such to move from place to place anymore after15 years of service, so in came the Escape and out went the 'burb.