BMW How To Video – Electric Water Pump Replacement DIY – N51, N52, N54, N55 6-Cylinder
Does your BMW need a new water pump belt? Maybe not ….. ever!
The new BMW N-series 6-cylinder engines (N51, N52, N54 and N55 in the US) no longer employ an engine driven water pump. These engines are designed with an electrically driven water pump that is mounted as an accessory to the engine. This allows the engine management system to fully control and modulate the coolant flow through the engine, rather than being a result of engine RPM (Revolutions Per Minute, or speed). While this design surely has advantages in engine efficiency, power production and emissions, the pumps themselves have been showing failures in the 50,000 mile and up range.
Typically, as the water pump is failing, the engine management system will begin to reduce engine power due to the reduced cooling capabilities. Eventually, the engine will go into a safe mode and only allow idling and low RPM function.
The water pump is mounted in the area that historically has been reserved for the air conditioning compressor, at the lower right side of the engine. We have seen various electric water pump replacement procedures, some suggesting that the complete front of the vehicle be removed (to include the bumper, lights, radiator support, radiator, A/C condenser, etc). However, there is a much easier method that will apply to most models that use these engines. We’ll show you these steps on a 2008 335i.
Since the thermostat resides beside the water pump, and the pump must be removed in order to replace the thermostat, we highly recommend that the thermostat be replaced when the pump is replaced. We normally would also recommend that the coolant hoses be replaced while the system is drained. However, in these models the only hose that is readily accessible for replacement is the thermostat to water pump hose. We would suggest replacing this hose, but the others would require quite a bit of additional work.
• 3/8” drive sockets, universal joint, extensions and ratchet, 8mm – 13mm
• 17mm open-end wrench
• Various flat-head and Phillips screwdrivers
• 10-amp battery charger
1) Safely and properly raise and support the front of the vehicle. This repair task can be performed with the vehicle on jack-stands or using drive-on ramps.
2) Remove the forward under-chassis splash panel.
3) Disconnect the power steering cooler hose assembly mount on the passenger side and move the hoses rearward and toward the driver side. Use a piece of wire or a cable tie to hold the hose assembly out of the way.
4) Remove the two mounting nuts on each swaybar mount and lower the swaybar. Move the bar toward the rear of the vehicle and tie it up with a section of wire or a cable tie.
5) Remove the water pump harness plug wiring connector plug.
6) Place the coolant catch pan under the water pump. Using the flexible hose clamp driver, loosen the hose clamp on the thermostat to water pump hose (the nipple that is facing the rear of the vehicle) and carefully pull the hose off the water pump inlet nipple. This will drain most of the coolant that is in the water pump, thermostat and local hoses.
7) Use the flex driver to loosen the water pump outlet (supply) hose. The hose nipple points toward the passenger side and is above and to the rear of the thermostat (look at the new water pump to help locate the nipple and hose). We cannot remove the hose as it is solidly mounted. We will pull the water pump from the hose, in step # 13.
8) Remove the two lower water pump mounting bolts, using an E12 Torx socket.
9) Place the coolant drain pan under the forward end of the thermostat and water pump. Disconnect the radiator to thermostat hose (large plastic hose elbow at the forward end of the thermostat) by pulling out the locking wire on the quick disconnect fitting and pulling the fitting off of the thermostat nipple. Allow the coolant to drain.
10) Remove the two thermostat mounting bolts.
11) Pull the ground cable from the mounting clip that is affixed to the water pump rib, just forward of the upper water pump mounting bolt. Look at the new pump and use a light to locate the ground cable and the clip. Pull the cable out of the clip and push the clip off the rib (toward the passenger side), using a long screw driver.
12) Remove the upper water pump mounting bolt using the E12 Torx socket, universal joint, extension and ratchet. Move the disconnected radiator to thermostat hose upward and the thermostat toward the passenger side to allow the socket assembly to be inserted upward between the heater return hose assembly and the subframe crossmember, to the upper water pump mounting bolt. See the new water pump for the bolt location.
13) Pull the water pump down and out, while pulling the outlet nipple out of the engine supply hose (this is the hose that we loosened the clamp on, in step # 7).
14) Disconnect the thermostat electrical harness plug.
15) Disconnect the quick disconnect fitting on the heater return hose to the thermostat and pull the hose end from the thermostat. This is the hose that runs along the front subframe rail and then connects to the thermostat just above the larger plastic elbow that we removed in step # 9. Look at the new thermostat to help locate the hose connection on the vehicle.
16) Gently pull the thermostat down and out. Note that there is one final hose connection to remove before the thermostat can be fully removed.
17) Using the hose clamp flex driver, loosen the hose clamp on the cylinder head to thermostat hose and pull the hose from the thermostat nipple. The thermostat can now be fully removed (along with the still attached thermostat to water pump hose).
18) Install a new water pump to thermostat hose to the new thermostat or transfer the original hose if desired.
19) Connect the thermostat to the cylinder head to thermostat hose (from step # 17). Note the orientation of the hose clamp and install it so that the clamp can be tightened after the thermostat and water pump are fully into place.
20) Move the thermostat up into its general location.
21) Connect the heater return hose to the thermostat (from step # 15).
22) Connect the thermostat harness connector plug.
23) Position the hose clamp on the engine supply hose (that connects to the side discharge outlet on the water pump) so that it will be accessible with the flex driver after the pump is in place.
24) Install the water pump up into place, inserting the discharge/outlet nipple into the engine supply hose. Loosely install the two lower mounting bolts to hold the pump in place.
25) Install the upper water pump mounting bolt in reverse of step # 12.
26) Tighten all three water pump mounting bolts.
27) Install the ground cable mounting clip to the water pump rib and mount the cable into the clip.
28) Connect the heater return hose to the thermostat. Make sure that the quick disconnect fitting is fully seated on the thermostat nipple and the locking clip is properly seated in the fitting.
29) Connect the radiator to thermostat hose to the thermostat. Make sure that the quick disconnect fitting is fully seated on the thermostat nipple and the locking clip is properly seated in the fitting.
30) Tighten the engine supply hose to the water pump outlet nipple.
31) Connect the thermostat to water pump hose to the water pump inlet nipple and tighten the hose clamps on each end of the hose.
32) Connect the wiring harness plug to the water pump.
33) Install the sway bar and mounts.
34) Install the power steering hose assembly mount.
35) Prepare to fill and bleed the cooling system by having the following items ready and at hand:
- One full gallon of BMW coolant mixed with one gallon of distilled water (two gallons in total.
- Coolant filling funnel
- 10 amp (or larger) battery charger
36) Unscrew and remove the bleeder plug on the expansion tank. Using the no-spill funnel, fill the system until coolant runs from the bleeder port.
37) Replace the bleeder plug, remove the funnel and install the expansion tank cap.
38) Connect a 10-amp battery charger to the under-hood charging terminals and turn the charger on and set to its 10-amp range.
39) Turn the ignition on (do not start the engine), heat to full hot with the blower on low. Press the throttle fully to the floor and hold for 10 seconds, then release. This will activate the self-bleed process. The process takes about ten minutes and is fully automatic. During this process you should be able to hear the water pump moving the coolant and turning on and off.
40) Once the self-bleed process is complete, remove the battery charger. Remove the expansion tank cap and check the fluid level. Add coolant if needed to bring the level up to full. Replace the cap.
41) Check for leakage at any of the connections under the vehicle.
42) Install the splash shield.
43) Lower the vehicle.