OEM electric water pump control strategy?
 

Hi guys, I've been doing some digging on factory EWP's and I haven't found much information regarding the control strategy for these units. From what I gather so far, automakers are using PWM to vary pump speed.

Are these pumps activated only when a certain temperature threshold is reached, or do they run constantly only varying coolant flow? What kind of flow numbers are these factory electric pumps producing?

I recall reading a BMW press release for the 330i and it sounded as though the pump was off until the engine warmed up. Though this begs the question as to whether localized hot pockets could damage the engine.

I understood that most engines had a small "back channel" that when the thermostat was closed would allow a small amount of the coolant to circulate around the engine. This would even out the temperatures, and also allows the now-heated coolant to come in contact with the thermostat due to the minor circulation...

Or is that an old wives' tale?

I have the same understanding as Plasticuser for traditionally cooled vehicles. I would imagine a similar setup for electric pump vehicles, meaning the pump would be running at least a little even when cold.

It would seem to me a good idea to have the WP start running very slowly, part way into the heating cycle.

I suspect that EWPs will eventually become standard equipment on all vehicles as they are quite simple and a more efficient way to circulate coolant.

BTW, What is PWM? I assume it is pulse width modulation? I would guess that probably is the most efficient way to have variable speed from a 12VDC motor.

...the 1.4LT Cruze engine has an "electronically controlled" thermostat that's regulated by the engine's ECM: raising temperature during constant, light-load, operation for better fuel economy; and, reducing coolant temperature during WOT, high-load, operation for "safer" operation under full turbo-spooling (higher 'effective' compression ratio).

That sounds like a smart strategy.

What is the power consumption of an electric water pump at different loads? Does anyone have a graph? Is it always going to be less than an e-fan on a radiator, where putting the energy into moving the coolant faster is a strategy on the highway to prevent e-fan use?

Depending on the coolant system, moving the coolant faster may or may not result in more cooling. I have heard of cases where moving the coolant through the radiator too quickly results in less cooling.

I don't know where you heard that, but I can guess why you heard that :)

The faster the coolant circulates, the less temperature difference there will be between the inlet and outlet. The coolant being returned to the engine will be warmer.

HOWEVER:

Because the flow is greater, the amount of heat being transferred to air by the radiator is greater, and the amount being removed from the engine is greater.

100 gallons of 150F coolant cools just as well as 50 gallons of 110F coolant in the same amount of time.

There is a loss, however. Heat likes to travel down a hill, and the steeper the hill, the better it travels. A point is reached where no matter how fast you circulate the coolant, the temperature is so close to the engine's temperature that not much heat moves. you won't see this effect in your civic or F150, however you might see this effect in an F1 or Indy car.

plasticuser is right.
Also under special circumstances (high temperature and the pump running very high rpms) the pump can cavitate, which will reduce flow - and the engine suddenly overheats.
-mort

Yes its true.
I would never run the engine with the pump off for more than 10 or 20 seconds even when cold at idle.