Hi folks,
I've posted this warm-up data in the General area because block heating should help any hybrid. It is especially useful for Toyota systems but it should help all hybrids with an auto-stop capability.
I have been recording the first warm-up: (1) using "N" while parked, (2) "D" while parked, and (3) "P" after using the block heater. The battery current scale is on the right and the air mass flow data in grams per second on the left. I've offset the zero scales so the upper battery currents are separate from the lower air flow data:
This is a North American NHW11, 03 Prius that has the HC emission system and extended warm-up. The chart shows the block heater is especially useful for my NHW11 03 Prius. The data suggests:
1) ~80 grams / 2.81 oz - "D" stationary
2) ~78 grams / 2.76 oz - "N" stationary
3) ~26 grams / 0.92 oz - "P" with block heater, stationary
Although "N" had slightly less fuel burned compared to "D", "N" defeats the auto-stop. For "N" to be useful, it needs a timer, say 60 seconds, before flipping over to "P" or "D". But the quantity of fuel saved does not justify the savings when stationary. Worse, "N" does not come even close to the block heater savings.
Remember, this is a 2001-03, North American Prius, with the HC system. European and Japanese versions will not have the same "D" warm-up cycle. I don't have data for other hybrids however I suspect they would also benefit.
Bob Wilson