If I may, Yes, it does.

Depending on the temperatures the FE profile is not much different than that of the Prius. The biggest issue is the warming up of the engine in order to reduce emissions. During that time the engine RPM is often high enough (1500 RPM) that the car barely needs gas pedal input to drive out of the residential areas. At this point ICE Auto Stop is absent as well.
Once it warms up - especially on the very cold days- the electric regen and assist come back to full function which also includes ICE Auto Stop and EV-only assist (both at slow or high speeds). With a cold car in a typical winter day, the first five minutes can read as lowsy as 11 mpg (or possibly even less).

A block heater though, does wonders for the HCH as it does for the Prius.

Cheers;

MSantos

How hot does that block heater get up to to have an impact? Engines run at 100s of degrees fahrenheit - does it get that hot, or just bring it up to room temperature?

That would be another nice feature of a real Plug-In Hybrid - if the engine block could be heated on a timer just by plugging it into the wall, no additional block heater required.

Prius 2006, bought September 14:

Good question.

Well, it gets hot enough to really make an big FE difference (it depends on the outside temps of course). For instance, during the spring and fall my FE remains relatively unchanged from my summer FE if I use a block heater.

On colder winter days I can cut a 5-10 minute warm-up in half or better. To me this is very important because my trips are all under 10 miles and therefore not enough to have a full warm-up for maximum FE.

My block heater is a 400W (nominal rating) element.

Here's my setup:


Cheers;

MSantos

Interesting. From a bit of googling, it sounds like that will get you to room temperature on a very cold day, or part of the way to normal engine heat on a warm day. Note that that means it'd be useful to run even on hot summer days if you knew you were heading out in a bit.

One kind of cool thing about these Hybrids is their small gas engines make them candidates for smaller, lower-wattage engine heaters (read: cheaper).

Prius 2006, bought September 14:

Well, "room temperature" is a reference point that is very subjective - perhaps even misleading.

The heating element itself is hot enough to inflict serious injury is touched while in operation. Obviously, it is expected that the mass of the engine will absorve this heat. and hence remain warmer than "room temperature".

But if we insist on a reference point, the engine - as a block of metals and fluids - will be of a measurably higher temperature than the immediate surrounding air. And that is the key to its usefullness and benefit. The engine warm-up, emmisions and FE is greatly improved.

Cheers;

MSantos

Well by room temperature I mean closer to 70F when it's Winter outside and further from 500F - where a catalytic converter would benefit immediately. Getting the block to 500F would be costly electric-wise though, and maybe dangerous.

Prius 2006, bought September 14: