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I saw this question in the cue recently.
I know of no cars that are in production that use electric water pumps. I am assuming that it's continuity issue related to failure rates and engine damage risk.
I believe this question is directly related to the electric oil pump question but felt the desire to ask to validate any misplaced beliefs I have.
Does anyone know of a production vehicle that uses an electric water pump?
If not, why not?
The W12 engine produced by VW utilizes both mechanical and electric water pumps (underlined with green). According to VW's documentation:
The cooling system of the Audi A8 with W12 engine is made up of the following components:
- Water pump in cylinder block/crankcase driven mechanically by Poly-V belt
- Map-controlled electrically operated continued coolant circulation pump -V51 as back-up for mechanical water pump and for continued coolant circulation
There are more details provided on the electric pump:
The electrically driven continued coolant circulation pump -V51 is located in parallel in the large cooling circuit in the return from the radiator. The continued coolant circulation pump -V51 has two functions:
To provide back-up for the mechanically driven coolant pump at low engine speeds and to ensure adequate coolant circulation. -V51 is actuated via the additional coolant pump relay -J496 by engine control unit 1 -J623. Map control is employed to switch in the continued coolant circulation pump -V51 as required. The parameters used for this are the engine speed and the coolant temperature supplied by the coolant-temperature sender -G62.
Switching levels:
Cut-in: < 840 rpm and > 108 °C Cut-out: > 3000 rpm or < 106 °C
To circulate the coolant during continued coolant circulation
Continued coolant circulation is described as well:
Continued coolant circulation
Continued coolant circulation is regulated by engine control unit 1 -J623 in line with a map.
Both the activation condition and the continued coolant circulation time are determined from the following parameters on the basis of an arithmetic model:
- Coolant temperature (from coolant temperature sender -G62)
- Engine oil temperature (from oil temperature sender -G8)
- Ambient temperature (from intake-air temperature sender -G42)
The activation condition and continued coolant circulation period are constantly calculated from the time of starting the engine.
For continued coolant circulation, the pump -V51 and radiator fan -V7 are actuated in parallel.
The maximum continued coolant circulation time is limited to 10 minutes.
The map-controlled engine cooling thermostat -F265 is fully actuated during continued coolant circulation.
Examples of activation condition as a function of ambient and coolant temperature:
- Ambient temperature 10 °C, Coolant temperature 110 °C
- Ambient temperature -10 °C, Coolant temperature 115 °C
- Ambient temperature 40 °C, Coolant temperature 102 °C
BMW abandoned their mechanical water pump in the 3 series when they moved to the E90 generation in 2006. The electric pump is the only pump. A quick search reveals that all other typical cooling system components (i.e. thermostat) still exist, so even when the engine is warming up the coolant circulates. This is probably to prevent hot spots which could happen if the pump just stopped.
There is a flow sensor for feedback so if the pump starts to fail the ECU can set a trouble code. E90 owners have reported low flow code as much as a month before total pump failure, but I'm sure reliability and failure rates vary by make/model just like anything else.
It seems there are two primary benefits to electric pumps:
Running with the engine off seems trivial for non-turbo and non-hybrid cars until you consider that most European cars turn off their engines if they come to a complete stop for more than a couple seconds to conserve fuel. The ability to circulate warm coolant through the heater core with the engine off becomes critical for driver comfort in cold climates.
In answer to the original question you asked, yes, I happen to know for a fact that the Mk3 Volkswagen Golf VR6 uses an electric water pump. The purpose of this pump is to keep hot coolant circulating after the engine has been shut off to prevent hot spots and heat soak causing damage. However, this is used in tandem with a mechanical pump which runs all of the time that the engine is in operation.
If you're looking for cars which use only an electric water pump, then I can't name any. This websites seems to imply that some modern cars have abandoned the mechanical pump altogether but doesn't name any specifically. I could quite believe that some competition cars run electric pumps and that it may be a technology we will see in road cars at some point but I don't know what basis the linked website has for claiming that some modern cars have already forgone the mechanical pump.
UPDATE
Looking at this link to the Gates electric water pump catalog, it woudl appear that I've stumbled across a number of cars that appear to use solely an electric water pump. (Most of these are hybrid cars).
These include; 2013-12 Toyota Avalon, Camry Hybrid; Lexus ES300H 2.5L Electric, 2012-10 Lexus HS250H 2.4L Electric; 2011-07 Toyota Camry 2.4L Electric, 2014-10 Toyota Prius; Lexus CT200H 1.5L, 1.8L
The Toyota hybrids use an electric pump (at least Prius), or a combination of electric pump for the heater core and mechanical pump for the engine (RAV4 hybrid). I assume many other hybrid cars also use an electric water pump. The benefit of an electric pump for the entire system is having heat with the engine turned off, and reduced fuel consumption.
However, a single pump is suboptimal, as it both cools the engine and heats the heater core, so that's why it may be more optimal to have two pumps, like the RAV4 hybrid has. Then the engine maintains heat better when the heater core needs to be warmed by circulating coolant, and the radiator doesn't have water flow. Of course, eventually the heater core acts as a radiator, so eventually the gasoline engine needs to be turned on in extremely cold weather to provide a primary source of heat.
I don't know why the RAV4 hybrid has one mechanical (engine cooling) and one electric (heater core) pump and not two electric pumps. Perhaps Toyota didn't consider electric pumps reliable enough for such a critical application in a car that's supposed to be reliable.
