Great thermal management

Our 15 Prius V gives us a consistent 45 mpg in warmer weather. Although the mileage has dropped to about 38 mpg now that it is colder, I am impressed with the thermal management. I have a ScanGauge to monitor coolant temperature, RPM, battery current and mileage. Our car is kept in an unheated garage.

This week the temperatures were in the mid 20's as indicated by the outside temperature display.

When I pressed the start button, the ICE kicked in after about 10 seconds and ran at a fast idle (1350 rpm). The first traffic light is about a mile from our home. I pull out of the driveway and head towards that light (45 mph speed limit). I see that battery current is about 60 amps and the ICE is not assisting for the first 1/2 mile. After that 1/2 mile mark I see the battery current suddenly go negative (charging) and you can feel more of a coupling between the ICE and the wheels.

As the temperature reaches about 105 degrees, the first bar of the heater fan display appears. I get a little fogging of the windows. At about 115 degrees, the second heater fan bar appears. By the time I stop at that first traffic light, the temperature is about 130 degrees, the ICE remains on, the fogging begins to dissipate and I now have multiple bars showing for the heater fan. The coolant temperature is not increasing because the idling ICE doesn't produce much heat and the heat is being removed to warm the cold cabin.

I drive on to the next light and by the time I reach that next light, the temperature is only about 135 degrees and the ICE shuts off as I remove my foot from the accelerator. The temperature only rose a little in that 1/4 mile drive because the heater fan was running near high. Waiting for that light I can see the temperature drop pretty quickly from 135 to about 110 degrees. Before the light changes the ICE starts back up.

As I drive away from that second light, the temperature gradually reaches about 150 degrees, the cabin has begun to warm up. I can see bars start dropping off on the heater fan display. It is sort of an equilibrium point where not so much heat is required in the cabin and the coolant temperature has reached 150 or more. From that time on, the ICE shuts down each time I release the accelerator. Stopping for a light doesn't cause the coolant to drop enough to cause the ICE to restart while sitting at a light.

In about six or seven minutes I am in good mileage mode even in cold weather. It's a pretty remarkable system.