When does the Thermos pump go on ?

When the engine is cold, the pump comes on to move the warm fluid from the thermos into the engine to sped warming and minimize emissions. After you've been driving a while and the engine is warm, when you shut down the hot fluid from the engine is pumped into the thermos, ready for the next start up/shut down cycle.

 

Where are you, lowspeed? Please update your profile. Only North American Prius have the thermos bottle, so if you're not in NA, don't worry. The dealer can test the pump to make sure it works; they plug into the CAN and tell the pump to run, if it doesn't, bad pump. There are no warning lights. When the coolant is warm, the pump can be almost silent.

<div class='quotetop'>QUOTE(lowspeed @ Nov 25 2007, 08:54 PM) [snapback]544124[/snapback]</div>

 

The entire water circulation system in the Prius is filled with the coolant. The hot coolant is circulated from the storage tank to the engine block and the cold coolant from the engine block is circulated to the storage tank. Neither component is ever without coolant.

There is a multi-position valve and an auxiliary pump which determines which way the coolant is circulated.

1. Preheat operation: Circulate the hot coolant from storage tank to engine block. The auxiliary pump is doing this circulation and is what you hear when the Prius starts up when cold. The radiator is also out of the loop here, which is controlled like in a normal engine with a thermostatic valve.
2. Engine warm-up: Circulate the coolant through engine block and heater core. The storage tank is out of the loop here. The auxiliary pump is off here and the regular water pump is doing the work as in an any conventional car. The radiator is still out of the picture, until the coolant has reached operating temperature.
3. Driving: After the engine block has been warmed up the valve moves into its warm engine position which lets the hot coolant circulate through the storage tank, heater core and engine block. The radiator has its own valve as mentioned already. That is the normal warm engine mode.
4. Storage – off mode: If the engine was sufficiently warmed up so that the coolant is at the same temperature as in the engine block and you turn off the engine nothing happens except for the valve changed to the position where the coolant in the storage tank is blocked and kept at that temperature as long as possible.

There is a thermostat in the engine block and in the storage tank. When you turn the car on it determines which is hotter the coolant in the storage tank or the coolant in the engine block. If the car has been off for a while then the engine block coolant will be colder and it will do what is stated in point 1 above. If you don’t drive sufficiently long enough to get to point 3 above and you turn off the car it will use the auxiliary pump to circulate the engine block coolant to the storage tank, because the engine block coolant will be warmer. If you drive long enough to completely warm the coolant to the same temperature everywhere then when you turn the Prius off if will not use the auxiliary pump at all since there will be no need to do so.

 

Please refer to page 38-41 of following presentation.
http://john1701a.com/prius/presentations/2...entation_38.htm

Ken@Japan