In another thread Patrick Wong wrote: A pleasant surprise; I didn't know about this little detail before. In a short time, I got to thinking about how fast the ICE cools in cold temps. Whether you are on the initial warmup routine trying to get to 157 degF, or fully warmed up and in S4, ICE temps (via ScanGauge) fall very quickly and at around 135 degF IIRC, (or is it 110 degF ) ICE comes on just to reheat the ICE. The pump is shown in the coolant system diagram on page 4-10 here, but there is no further discussion of it's operation. Is the electric engine coolant pump always On, like the inverter coolant pump? Is the pump turned On/Off by the climate control system? Would there be any FE gain by hacking the electric coolant pump with a manual On/Off switch so that if you wanted you could prevent heat being drawn out of the ICE when stopped with the ICE OFF? By cycling hot water through the heater core and of necessity through the block, does the pump also play a role in evening out temps in the block and minimize hot spots in the block? Would this be a good reason not to disable it when the car is stopped and the ICE is Off?
First I'll note I've installed a warmer thermostat, 88 C which has improved cabin heat, I recommend it, more info- http://priuschat.com/forums/gen-ii-...bleshooting/58026-radiator-temperature-2.html I've heard the cabin air coolant pump run , a subtle buzz behind the dash when sitting in the car at a stop. The pump is mounted close to the firewall . I've heard it cycling on and off when sitting and waiting in my car, I would toggle the cabin air temperature up and down making it run more and less, verifying its operation. I do not use auto air, it is easier to hear the pump when the fan is on low speed. When the engine coolant temperature would go below 150 F, the ICE would start and run until the temperature would go up. My car has 182k on it, so my pump may be noisier than most. I've done a quick search for the part number and could not find one. From my observation, this cabin coolant pump only runs when the desired air temperature for the cabin air requires it, so any extra wiring to turn off this pump is unnecessary..
