Curious behavior of the ICE - just checking!

Completely normal. The ICE provides almost all of the heat for cabin heating and defrost, so it runs more in cold weather. There are two small electric heaters that also help.

Tom

 

just for re-assurance yes it is normal. Commonly I will start my day with heater completely off for the first 5 minutes so the ICE warms up quicker (even the non hybrid car). If I do have the heater on I will turn it off at stop lights if its still warming up so that the engine will shut off.

Just to add about how the ICE provides heat because I am under the impression that you think the heat in a car comes from electricity. Most cars including the Prius use the warmed up Coolant / Anti-Freeze from inside the engine, The engine starts to get hot and the coolant keeps it at a regulated temperature, the coolant circulates into the heater core the heater core gets hot from the coolant and then outside air through the ventilation system passes through it and picks up heat.

 

As posted above, perfectly normal.

Before Prius is fully warmed up, you can have the coolant drop below about 63C while waiting at a light. If the A/C is calling for heat, the engine will start.

Your interior temp sensor may have been just at your set temp so when you dropped it a degree it allowed the engine to shut down. Note that the -actual- interior temp is not necessarily the same as the sensor temp.

Once you get the engine coolant above about 62C - and - exceed about 40 MPH, you get into "stage 4". This allows the engine to shut down if "not needed". It will also shut down at stops earlier in the warmup cycle, just not when moving.

Note that for awhile after getting the coolant to 62C it will still drop quickly when stopped, as the parts are still not fully warmed up, and during this time the engine may start at lights. It takes about 20 min of city driving to get Prius fully warmed up. It WILL blow nice hot air after only a few minutes, however.

I shut off the A/C auto function using the steering wheel switch during warmup when stopped at lights to keep the engine off while waiting.

 

Sounds totally normal. Try selecting the off fan position (no need to muck w/defrost). The ICE will probably also stop.

 

Just turn off the climate control with the button on the steering wheel while stopped.

 

We're all complaining about how cold it is, how icy it is, and how difficult it is driving in deep snow, while Pat is sitting in his car sweating, waiting for the A/C to bring the thing to a reasonable cabin temp.