Allen

My car is a '08 535i. The water pump is an electric driven pump motor. What tells the water pump to start pumping when the car is heating up after initial start...from cold? In the old days, the thermostat was inline and blocked the flow of water until the thermostat determined the water was hot enough, then it opened up and the water flowed. Do the new cars use a thermostat wit a valve (that can stick), or does the computer just leave the pump off until it sees the water temp raised to certain value? I'm wondering if instead of a "true" thermostat, our cars just have a water temp signal that goes into the computer and the computer just turns the pump on as needed....??

pukka

I could be way off, but I always thought the main reason for using an electric water pump was less parasitic loss. The engine has one less accessory wheel to turn which meant more power to the wheels. I also suspect an electric pump is lighter than a mechanical one.

With that being said, I couldn't imagine the water pump not running constantly. The engine block and head(s) are aluminum, which have far less heat tolerance compared to iron.

Allen

You are right...I really should restrict my question to the start up portion of the "cycle"...I don't think the water pump runs when the engine is cold...that's really my question. However, I am almost positive that once the engine has reached full temperature...as determined by a temp sensor...the pump runs all the time after that...like when the old-style thermostats would "open up". THEN, the electric radiator fan is used to regulate the temp.

Allen

I hate to drag up an old post...but this is still something I wonder about. Does anyone have input on this?