What is the purpose of a thermostat if the water pump is electric

The engine will warm up quicker if the thermostat does not allow heat transfer out of the engine.

" If it takes more than five minutes for the heater to produce heat, it is a sign that the thermostat is stuck open, allowing all the coolant to flow all the time."

 

Am I missing something?
But all computers need input of data to make decisions.
Therefore you'd still need the "information" provided by a thermostat in conjunction with the electronics.

Like nearly all vehicles today the computer controlled aspect of anything is usually there to make the operation more efficient.

Automobiles in the 60's had NO real computer controlled functions.
They were easier to fix and work on in your garage.
But they were far less efficient than today's automobiles.

 

An automotive thermostat is not so much a temperature sensor as temperature-activated tap, closed when cold (blocking flow), gradually opening as the coolant temperature climbs. There is a separate temperature sensor, sending info to the computer.

(I went down the same rabbit hole, btw.)

 

OK.
I concede my ignorance.
But....the vague semantic difference between a Thermostat...which I evidently ignorantly defined as a temperature sensor and the evidently separate "temperature sensor"...which is NOT the thermostat...well...I can forgive myself for this mistake.

So then my follow up question is:
If the thermostat- Is a temperature activated tap...then IS it the thermostat-tap that is setting the parameters for the water pump behavior? Or is it the computer and the temperature sensor.

And if the Thermostat and the Temperature sensor both hit on the same woman at a bar, who get's the date?

 

On a typical automotive thermostat there's no electrical wiring, no connection to the computer. It's really an archaic contraption. I'm not sure what's inside, some sort of temperature sensitive wax, bi-metal strip? It has a strong spring, a rubber sealing gasket.

If you suspend one in a pot of water and slowly raise the temp you can see it in action. With a previous car I was noticing when commuting early morning on a freeway, cool weather, against the flow of traffic so no slow downs, as I got to my turn off the temp gauge needle was down at the bottom (you'd never get this notice with a Prius ), and after some reading, decided to try replacing the thermostat.

I took the new one and the old one, suspended both in a pot of water, along with a thermometer. Interesting. The old one opened sooner as the temperature climbed, and closed later. Also it's gasket was frayed, missing a bit around the edge. Basically letting coolant flow into the radiator at too low a temperature, and never completely shut.

 

Huh? When the engine and coolant are not hot enough overall to require coolant flow through the radiator, the thermostat blocks flow to the radiator, but coolant still circulates in the engine, thanks to the water pump. If you tried to control temperature instead by stopping the water pump, what's going to circulate coolant past localized hot spots?

 

Yes, water pump and inverter pump should both be running constantly in normal operation (Ready).

 

Another wrinkle: there are two coolant circuits in the Prius: engine and inverter. Are there thermostats in both? I'm guessing no, but clueless, lol.

 

The engine water pump is controlled by the engine ECU. The ECU relies on the temp sensor in the cyl head to determine engine temp.

The purpose of the thermostat is to keep coolant from flowing to the radiator until the temp reaches -180 degrees F.

It is possible for the pump to run while the thermostat remains closed, to equalize temp throughout the engine.

 

All engine water pumps must run continuously. This is to "scrub" bubbles of boiling coolant off the metal surfaces in the head (from Auto Mechanics books, not my idea). The engine has two coolant paths or circuits, one low flow one through the heater then radiator bypassing the thermostat (and bypassed by the heater when it's off), but still a low flow circuit - think 3/4" hose. The other circuit is the high flow one when the thermostat is open. These generally use much larger hose - 1 1/2" and larger.
Race cars (dragsters) are different, but their engines only last a few minutes. Last as in they are destroyed after a few minutes of running in some classes. They usually leave the water pump off the engine as it just cavitates anyway at 7000 RPM.

The engine temp sensor is not related to the thermostat. The thermostat is mechanical (wax melting). Oh, and it needs the low flow circuit to be running so it can warm up. So does the temp sensor, BTW.

So the water pump, mechanical or electric, must run when the engine is running. Not sure if the Prius turns it off when the engine stops in "EV" mode, but I would think if the temp isn't close to thermostat opening it should turn off. But then again, turning it on and off a lot can shorten its' life.

 

How do you suppose residual engine heat gets to the heater core when you're coasting downhill or stopped at a stoplight on a cool day---assuming the engine was initially at normal operating temperature?