Allen

I know this is WAY off topic...but I have tried in the BMW forums and can't get any meaningful input...I'm sure this topic applies to most all new cars. Anyway...moderators can delete this if necessary.

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, 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 with a mechanical 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....??

Juha G

Firstly the engine coolnt water pump will allways be on when the engine is running as the coolant must circulate around the system at ll times. Secondly wheather the water pump is driven off of the crank or by an electric motor, has nothing to do with how the coolant temperature is controlled. Your 535 has a thermostat like most cars, which mixes cool water from the radiator into the hot side as necessary to keep the coolant temperature on the engine side at a desired constant level.

sonny1

The DME computer tells the pump to start,same with the thermostat. is all electronic controlled.
Sonny1.

Allen

My understanding...on older pre-computer cars...is that when the car was first started...the thermostat was closed...keeping the water flow OFF...allowing the engine to reach operating temp quicker. Once operating temp was reached...the thermostat opened allowing water flow...then remained open all the time. Is that not correct?

How does the themostat "mix cool water from the radiator into the hot side"? Does it open/close to allow water to flow or not flow into the hot side from the radiator? If the thermostat is opening and closing...how can the water pump run constantly...it would be pumping against a closed thermostat?

I told you I'm confused...lol...

Allen

The DME controls the opening and closing of the thermostat?

Ed Hughes

It keeps the water circulating in the engine to warm up, then opens up the entire system when temp is reached to allow cooling. As noted before, the water pump will always run when the engine is.

Allen

Ok…I think I’m about to get it. The water pump runs any time the engine runs. When the engine is below temp XX…thermostat (TS) is closed and radiator is bypassed…getting engine up to temp quickly. When the engine exceeds temp XX…TS opens allowing water to flow through radiator which begins to cool the engine. Now the engine drops below temp XX and TS closes again…engine temp increases to exceed XX…TS opens…temp decreases…and cycle goes on like that…is that right?

Now to my specific question…which I think Sonny1 answered. The opening/closing of the thermostat…in the old days, that was a mechanical diaphram, that caused the open/close based on water temp. In todays cars…is the "thermostat" actually just an electronic valve that is opened/closed via the computer...when the computer sees the engine temp high or low?

I apologize for my confusion…I’m an Engineer and I just can’t let it go until I understand. This board is the best place I know of to get correct information…and I do appreciate it.

Garth S

Both your pump and thermostat are 'electronic' ..... and take their ques from the DME - the pump has a duty cycle , so does not run 100% of engine run time as do mechanical pumps.

The pump & thermostat are usually replaced as a pair, as are the mounting bolts - BMW has a love affair with aluminium bolts that are one use only.

Take a read here for a better description.

My older 535i (E34 is all mechanical, and parts are cheap - my W8 Passat has an electronic thermostat @ ~ $450 ...... technology advances with the newer 535i, where both are electronic - guess where the price goes .

Ed Hughes

I would still believe that electric pumps turn when the engine is running-just like a fuel pump, even if controlled by a computer. An engine builder is going to want to distribute/diffuse heat as evenly as possible, and flowing liquid would aid in this.

Stealth 993

There will be a green coolant temp sensor in the coolant rail, this turns on the pump.

XR4Tim

The Cayenne Hybrid has an electrically-operated shield that blocks off the impeller of the mechanical water pump during the first stage of the warm-up phase. They say that there is supposed to be no flow at this stage.
If BMW is trying to get the same result (quickest warm-up for lowest emissions), they are probably not turning the electric pump on at all until a certain temperature.

Anders T.

I am going to fit an electric pump in an old Citroen B11 1951.

http://www.mawsolutions.com/html/ewp80.html

The regulator to the pump is like a thermostate and I will try to run this combo without any thermostate at all. The downside of this is that the flow will be very poor until the engine gets warmer and the pumps speed up. This will increase the time until the cupe heater gets warm.

sonny1

Yep, completely,cheers,Sonny.