Prius Thermal Thresholds

Dan. · 03-28-2007, 05:03 PM

Disclaimer: I'm a Fuel Efficiency phreak. I do unusual things to save gas.

I've been reading on thermal mods the the Prius and I've read the articles on the Prius Stages. What I gathered is that stage transitions begin around 45c and complete around 85c.

So I deduced that the best (efficient) temperature to operate the Prius at is 85c (or possibly above).

Does anyone know what temperature is too hot? 110c, 120c, 130c, 140c? I just got the ScanGuage II so I'll have hard numbers next month.

Since my morning commute rarely lands me in S4, I think that my block temp is a slow progression from 20c to 80c. With a block heater, It should move up to 40c to 100c. With grill blocks possible 40c to 140c.

So when does heat hurt and not help efficiency? What temp is too hot? What temp turns on the idiot light for overheat?

I know it seems absolutely insane to do this in Texas, but please refer to my disclaimer.

PS. Prius refers to '07 Prius II

11011011

tochatihu · 03-28-2007, 07:43 PM

I suppose that all the good mpg stuff happens when your ICE coolant is above 85 oC. You would have to do a lot of 'thermal management' to get it above 100 oC. Prius is pretty darn good at shedding engine heat.

Anyway, if you can manage to exceed 100 oC, you are beginning to pressurize the rubber tubing that runs the coolant here and there. It is not to your advantage to do that.

The electrical fans will begin to spin and draw a hundred watts (or two) when that coolant gets above 95 oC or so. You don't want to throw that away, so plan to live your efficient life between 85 and 95.

It ain't hard.

I am not sure whe know what it takes to make the hot coolant light come. I've not seen it, nor have I heard it reported by others. Our best hope is that it would appear before the rubber tubing fittings detach.

PS: if you are a phreak, check in at www.cleanmpg.com

ken1784 · 03-28-2007, 09:17 PM

Japanese Prius Tech Manual says the thermostat specification is starting to open at 82C and fully open at 95C.
Cooling fans starts at 96C.
We see the typical coolant temperature is about 88C.

Ken@Japan

03-28-2007, 05:03 PM	#1
Dan. MPG Centurion Join Date: Sep 2005 Location: Houston, Texas Posts: 226 My Car: 2007 Prius Package: #3 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 2	Disclaimer: I'm a Fuel Efficiency phreak. I do unusual things to save gas. I've been reading on thermal mods the the Prius and I've read the articles on the Prius Stages. What I gathered is that stage transitions begin around 45c and complete around 85c. So I deduced that the best (efficient) temperature to operate the Prius at is 85c (or possibly above). Does anyone know what temperature is too hot? 110c, 120c, 130c, 140c? I just got the ScanGuage II so I'll have hard numbers next month. Since my morning commute rarely lands me in S4, I think that my block temp is a slow progression from 20c to 80c. With a block heater, It should move up to 40c to 100c. With grill blocks possible 40c to 140c. So when does heat hurt and not help efficiency? What temp is too hot? What temp turns on the idiot light for overheat? I know it seems absolutely insane to do this in Texas, but please refer to my disclaimer. PS. Prius refers to '07 Prius II 11011011 __________________ Dan is an official (Honda) Hydrogen Economy Convert! Houston Hybrid and Hypermilers Club <106mpg.com> Best commute = 14.3mi @ 114 MPG (sg2) Best (non-trivial) tank = 769mi @ 85.7 MPG (fcd) MPG Centurion-Hybridfest 2007-Prius II-26mi @ 106 MPG (sg2) Dan <11011011> @ CleanMPG.com

03-28-2007, 07:43 PM	#2
tochatihu Senior Member Join Date: Apr 2004 Location: Kunming Yunnan China Posts: 1,823 My Car: 2001 Prius Package: Pioneer #1 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 7	I suppose that all the good mpg stuff happens when your ICE coolant is above 85 oC. You would have to do a lot of 'thermal management' to get it above 100 oC. Prius is pretty darn good at shedding engine heat. Anyway, if you can manage to exceed 100 oC, you are beginning to pressurize the rubber tubing that runs the coolant here and there. It is not to your advantage to do that. The electrical fans will begin to spin and draw a hundred watts (or two) when that coolant gets above 95 oC or so. You don't want to throw that away, so plan to live your efficient life between 85 and 95. It ain't hard. I am not sure whe know what it takes to make the hot coolant light come. I've not seen it, nor have I heard it reported by others. Our best hope is that it would appear before the rubber tubing fittings detach. PS: if you are a phreak, check in at www.cleanmpg.com __________________ DAS Tochatihu, the Hopi hummingbird kachina

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
aerodynamic and thermal benefits of vent block	chronon	Fuel Economy	7	07-01-2007 12:48 AM
EV mode vs normal stealth thresholds for ICE	efusco	Prius Technical Discussion	12	04-23-2007 04:20 PM

03-28-2007, 09:17 PM	#3
ken1784 SuperMID designer Join Date: Dec 2003 Location: Yokohama, JAPAN Posts: 1,391 My Car: 2004 Prius Package: G Touring Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 3	Japanese Prius Tech Manual says the thermostat specification is starting to open at 82C and fully open at 95C. Cooling fans starts at 96C. We see the typical coolant temperature is about 88C. Ken@Japan