Electric water pumps are not only more efficient than belt or chain-driven water pumps, but they can earn carbon credits toward Corporate Average Fuel Economy (CAFE). Okay, electric pumps are nothing new as they have been used as auxiliary pumps for many, many years, to circulate coolant at low engine speeds for improved cabin heating, and even to provide some residual heating with the engine off (on some luxury cars, such as Mercedes).
But as the primary water pump on a mass-production, high-volume gasoline engine, an electric is somewhat new. It makes the most sense on a full hybrid, where it’s needed for the greater length of engine-off time (during idle stops). On a full hybrid, and along with an electric-drive A/C compressor and electric power steering, it also can contribute to eliminating the accessory belt. The Prius is an example.
But we’re going to see more and more electric pumps as the primary coolant-circulating pump on gasoline (or diesel) engines which are not hybrids, particularly when idle-stop systems come into greater use. The first prominent example is the 2.0-liter four-cylinder turbo on BMW, one example of where an electric water pump can keep coolant circulating through the turbo housing briefly, if necessary to cool the bearing. This engine came on stream first on the Z4, but now it’s migrating to the 3-Series and smaller models, so BMW can meet window sticker as well as CAFE.
The electric pump is computer-controlled, so it runs only when the coolant is at operating temperature. And because pump output is proportional to pump rpm, the computer just has to increase the current feed (or reduce it) as necessary to meet engine cooling requirements and cabin heating demand. The pump could be mounted anywhere in the engine compartment, and as you may have noted, indeed may be anywhere, such as at the cowl. However, the one on the BMW 2.0-turbo is at the right front bottom of the engine, exactly where it would be with a belt drive, but in this case, for convenient routing of hoses.
What this means is that the water pump is now as electronic as the A/C. The circuit connections must be clean and tight, and although the coolant temperature sensor is an obvious computer input, so may be inputs from the electric fans circuit, cabin temperature sensors, even the outside air temperature sensor. So also expect to see a full menu of trouble code diagnostics and perhaps even a data item for pump rpm.
Of course, auxiliary water pumps can’t be ignored, and if you know they exist somewhere under the hood, you can put them on the “to-check” list whenever they can be expected to come on. In the case of a Mercedes with one, a quick check with the engine off and the pump running tells you it’s working. On the Dodge Durango (of the 2001- 2009 model year period), the pump comes on under these conditions: vehicle speed under 30 mph, coolant temperature from 50 degrees F up (to 230 degrees F), front blower turned on, rear system heat set above halfway (more than 60%), and no applicable trouble codes. If vehicle speed is above 30 mph, blower turned off or coolant temperature above 230 degrees F – ANY of these – the pump turns off.
There are two trouble codes for the circuit: BO107E – circuit voltage low, and B1080—circuit open. And as we noted in the October 2012 issue, the new Dodge Dart with the 1.4-liter turbo, a Fiat engine, also has an auxiliary electric pump, to circulate coolant through the turbo housing (to cool the bearing) when the engine is shut off.
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