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 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

 

I have been watching the engine temperature in the Ford Escape for more than 2 years. If you are doing P&G with ICE off on the glide, the graph would look like a sine wave.

 

If you are happy on 140F Pulse and Glide driving, it's OK for me.
However, the most efficient coolant temperature is approx 190F and that's why the thermostat control exists.

Ken@Japan

 

I don't think you hear what I'm saying.

Getting ( well, keeping ) a water temp of 190'F is impossible in a Ford Escape during the city drive cycle. It has nothing to do with want, or not want, like, or dislike, being happy, or unhappy.

 

In the evening commute home, I have a stretch of about 5 miles (8 km) on flat and level streets that I can hold 28-30 miles per hour (45-48 km/hr) using cruise control. This is well after warming up the ICE and putting a good charge on the battery due to a decrease in altitude after leaving work. When the temperatures are below ~50F (10C), I can watch the coolant temperature fall off when running on battery. It becomes significantly more rapid as temperatures approach or fall below 32F (0C.) On those rare evenings I'll take the limited access, 50 miles per hour (80 km/hr) lanes since the ICE will soon run just to keep the coolant above 60C.

Bob Wilson

 

I would like to say it's not impossibe but hard or long way.
There are a lot of factors you take a lot of time to raech the optimum 190F.
- short city driving
- cold environment
- cold initial coolant temperature
- grill block is not enough
However, the 140F pulse and glide driving is not trying to set optimum temperature by Ford 190F thermostat mechanism.

Back to the original point...
Again, the 140F city pulse and glide driving is not optimum, and FEH is designed to run 190F optimum temperature.

Ken@Japan

 

More to the point...

I DO NOT DRIVE A PRIUS!
( Your rules do not apply. )

 

Hope every drivers know the optimum coolant temperature on your vehicle.
You will know it from the specification of thermostat open temperature.

Ken@Japan

 

Maybe we were not on the same wavelength.

I agree, for best, most efficient ICE operation, warmer is better up to a point.
At some point, it becomes futile to try and be warmer.

However, for stop and go, P&G operation... 190'F is not generally attainable... and trying to keep the engine this hot, in the Ford Escape, would require more gasoline overall, due to the fact you would have almost zero EV operation, if you tried to keep the engine block over 190'F.
-John

P.S. I think warmer intake air is more important than warmer water temp also.
The "top" stage of warm-up I think occurs sooner than a Prius, but I don't own a Prius so I don't really know.

P.P.S. Durning a long ( 700 mile ) trip at highway speeds on a 28'F day, my water temperature was hovering between 184'F and 188'F with sustained 2500 RPM for hour after hour with the radiator 90% covered up with canvas ( top ) and plywood ( bottom ). I really think it is correct to say keeping my car 190'F with P&G is impossible... more than difficult, but impossible in winter.

 

Bro, whats the graph for???