Block heater in 2003 Prius

Hi folks,

Here is some data recorded in December on a 32F day:

The major time units are 5 minute intervals, 300 seconds, and the minor intervals are one minute, 60 seconds. MG2 rpm is directly proportional to the vehicle speed.

INITIAL WARMUP (first 7.5 minutes)

The block heater after an hour brings the ICE block temperature up about 30C relative to the 0C ambient. MG1 receives a little heat and MG2 gets the least. Once the ICE starts, the cold coolant from other parts of the block dips the temperature down but it quickly recovers as the ICE idles. In my area, the block heater uses is a little less than $.03 of electricity.

During the warm-up phase, I shift the car into "N" at every opportunity since this results in the lowest, mass air-flow and fuel consumption. As the coolant temperature comes up, the mass air-flow decreases as the engine can run at more efficient fuel burn levels.

Once the coolant of the North American NHW11 (2003) Prius reaches 70C, the various warm-up states Ken@Japan discussed are available. For example, speeds above 35 mph allow the ICE to auto-shutdown all the way down to 0 mph or when the energy required is low enough. The final, warm-up state change occurs when the ICE auto-shutdowns while the car is stopped.

NORMAL HYBRID MODE (7.5 to 21 minutes)

During this mode, the car is driven like any other, fully warmed up hybrid. If you reset the MFD mileage indicator, you'll see typically 55 MPG. This phase ends when I exit the Interstate and regenerative braking slows my speed down as I enter the business district where my office is located.

In this mode, I try to avoid 39-45 mph by either speeding up or slowing down. This avoids transition through 42 mph that separates ICE ON/OFF mode versus ICE ALWAYS ON mode.

COOL DOWN (21-29 minutes)

Having entered the business district, I keep the speeds in the 25-35 mph range to maximize EV mode. This uses the battery charge to maximize my MPG. Extra NiMH battery charge can be lost by the 'self-discharge' so this motive energy is a good return on investment. Given the excessive ICE run times during warm-up, there is plenty of energy to put a charge on the battery on the next trip.

Bob Wilson