Has anyone used a FEH in colder than -15'F ???
Colorado and most of the mid-U.S. had an Arctic Blast last week.

Nights in my town were -15'F and days were about 0 to +5'F.

As posted before, I have my radiator blocked with a sheet of styrofoam to help hold in engine heat.

At 0'F my engine coolent was up to 170'F in about 7-8 minutes, and I could get my first engine shut-down. However, the car also has an air-intake temperature sensor. At this cold of a level, even at a 2 minute stoplight, the engine would kick back on in 20-30 seconds. Saving 30 seconds of fuel is better than nothing, but for sure not what I'm used to.

Over 3 days of sub-zero weather, and about 100 miles of city driving in it... I was in the 29-30 MPG range. ( there was snow on the roads also )

Wish I had a gas-only Escape during this time to compare.

The radiator block works great in the 20-30 degree range.
Even in the 20's, I can keep it above 40 MPG in the city.
I think at zero and below, the air-intake temp carries more weight, and the engine runs even if the coolent is hot.
Also, my mileage is down, because at 0 degrees my engine had a fast idle, of about 1300 RPM the whole time. Even after 45 minutes of driving, the idle speed kept up at 1300. ( Normal is 1000 to 1050 )
-John

 

Interesting. I guess my driving profile is not right for the hybrid. Seventy-five percent of my dirving is long-haul, high speed (between Phoenix and Colorado). In town I drive less than 60 miles a week.

 

Seventy-five percent of my dirving is long-haul, high speed (between Phoenix and Colorado). In town I drive less than 60 miles a week.

This has got to be the most common "quote" I hear. When in fact you can never tell when you will end up using any part of the hybrid technologies. My mother-in-law drives an 05' Toyota Prius. From her commute, she travels 1000 miles/week on all highways. She gets around 50 mpg on with a 10 gallon tank (do the math, not hard.)
Maybe what you meant to say is the FEH isn't for you and maybe another hybrid car is more for you. One think I have definitely learned from several websites is that when considering any kind of car, you need to find the one car is better for you rather than making one "fit" your life style.

Between me and my mother-in-law we have 4 hybrids. 1 FEH, 1 Prius, and 2 Hylander Hybrids.

Good luck,
Rich

 

gpsman1 - I too have noticed a significant dropoff in mileage of the FEH below about 20F. This effect is also seen in my '06 Prius, but (perhaps) to a lesser extent. I don't know precisely why it is, but it seems more pronounced than a mere linear relationship to temperature. Also, not only does the ICE run substantially more at such low temps, but as the Prius display has shown me (I don't have the Navi option in the FEH), the instantaneous MPG is lower whenever the engine is running at all. For example, if I can usually climb a hill, using ICE with elec. assist, getting about 20-25 mpg in the Prius, I will be getting only 10-15 mpg on the same hill, under the same conditions, when the temp is 10F. I know the battery holds less charge as the temp decreases, so that would explain some of why the ICE is on more, but I'm sure there's more going on here than that. Any of you engineers care to proffer a suggestion?

 

So this begs the question...is there a benefit for installing a block heater so that when you first start up and leave the garage, the ICE is already warm? I never worry about it with my F150, but the FEH is a different situation...

 

If you assume an "ideal" thermodynamic cycle, one can show that for the Atkinson cycle, the work is proportional to the starting temperature (ie, air temperature, in absolute temperature, or degrees Rankine). Looking at the difference between a 20F and 80F day, the ratio of the work on the hot and cold days is proportional to (460+80R)/(460+20R) = 9/8.

Thus, if your cold day gets 32 mpg, the hot day would get 32*(9/8) = 36 mpg. Soooo, you start with a colder air temperature, you get less work and lower mpg's based just on thermodynamics. (Note that this has not accounted for mechanical effects such as colder bearings and lubricants taking longer to come up to temperature, etc.)

 

The block heats up so fast that I don't it would make a noticeable difference.

I'm trying to devise a way to heat the intake air to see if that helps any.

The radiator shield I had in place temporarily helped some but I didn't have the ScanGauge then and I was worried about overheating at highway speeds. I need to retry that now that I have the ScanGauge.

 

Unfortunately I think the only way to know is to try it.

I blocked different portions of the radiator, and over my test distance I was unable to see a difference. But there were issues with my test. 1. It was impossible to be consistant since traffic patterns changed. 2. My commute really only got the engine warm by the time I got to my destination, so it didn't examine the effects of engine cooling.

I was hoping to see the engine temp warm up quicker, with the radiator blocked, but was unable to see a difference. This is logical since the radiator is really only used when the temp gets high enough for the thermostat to open the valve. That would mean any difference with the radiator blocking would come from max running temp, and from decreased cooling rate. I tested neither of these.

In reference to the block heater, I know mine will go into EV in a shorter distance if I have to sit for a while. Certainly the engine is warming up while I sit, but so is the CAT. It is unclear what would happen if you just warmed up the block.

But get one and try it, and let us know!

 

Good point about the cat warming up. I've seen that the ICE will not shut down even though the water temp is well within the required range, so I believe the cat temp is also playing into this more than the block itself.

 

The CAT temperature is "infered" from the cylinder head temperature sensor and the intake air temperature sensor.

So far, these are the only two temperature sensors I've found on the vehicle.

When the engine is running....
If the cylinder head temperature is x, then the cat. temp. is expected to be y, and the coolent temperature is expected to be z.

When in the engine is not running...
If the intake air ( outside air ) temp. is x, the cat. temp. is expected to cool off at a rate of y/sec.

Same for the water temperature. I have not been able to physically find any direct water temperature sensor!

So yes, if we could make the intake air warmer, the computer will think the cat. is staying warmer longer in EV mode. Plus, if we could make the intake air warmer, we would get better vaporization of the gas, and a leaner mix would be used, increasing FE all the more.

It is unknown what this will do to you emissions. Seems like a paradox. Burn fuel to keep things hot to reduce emissions? Or not burn gas at all by perlonging EV mode, which will let the cat. cool below optimum?