http://john1701a.com/prius/presentat...ntation_38.htm
The hot water in thermos is only supplied to the cylinder head on starting up when the coolant temperature is less than 104F.
Prius is also easy to be cooled down on long downhill, but it does not happen on the flat road pulse and glide driving.
The thermostat
auto body part shuts off the valve to the radiator when the coolant temperature is less than the spec, 190F FEH's case.
Therefore, the radiator does not work below 190F, then the engine is trying to avoid for further cooling down.
Attached graph is an example taken by my friend during his 55 minutes Prius commute.
He is a very good pulse and glide driver and achieves more than 85 MPG on commuting.
The unit of X axis is in 0.1 second, so it took 30 minutes to reach the stable approx 88C(190F).
I would like to say please try to watch carefully how coolant temperature is changing using ScanGauge or something.
Regards,
Ken@Japan
