EBH-Transfer from Thermos Counterproductive?

The system is smart enough to only turn on the coolant transfer pump when the coolant in the thermos is hotter then the engine coolant temp.

The drop in coolant temp is caused by uneven heating of the coolant inside of the engine, and when the circulation pump turns on, its mixed with the colder coolant inside the engine block.

 

Thanks Bob. I often wondered about the drop in temp I see when the ICE fires up.

 

Keep in mind that although the Prius systems are "advanced", it still uses the interior heater "bypass" system that most other cars use. That is, even when the thermostat is not open, -some- coolant is allowed to flow from the engine to the radiator and back. This is the circuit that also supplies the interior heater, through another valve. The reason it's done this way is to prevent "hot spots" from developing in places of the engine block. It evens out the warmup.

This will also slightly drop the coolant temp at first, though it's not as big a factor as the coolant in the "farther niches" of the block. Note that the coolant pump (not the coolant -transfer- pump) only runs when the engine runs. It's the only thing belt driven off the crankshaft of the engine.