This article gives detailed instructions on replacing the water pump in a BMW vehicle with the N62 8 cylinder engine. Even though we used a 2005 645ci to perform this repair, this article can be applied to any vehicle with the N62 8 cylinder engine including V8 5,6,7 and X5 series vehicles with minor modifications to the repair steps.
A BMW N62 water pump replacement can help cure an overheating engine.
The BMW N62 V8 engine was the workhorse of all 8 cylinder E6x 5 series, E6x 6 series, E6x 7 series, and E53 X5 series vehicles produced till approximately 2010. It was the direct successor to the iconic M60/M62 V8s produced during the 1990s and early 2000s. The New Generation N62 V8 was produced with many enhancements to help increase fuel economy and decrease emissions...one of them being an improved coolant flow circuit to help reduce engine heat.
The BMW N62 engine was produced with a map-controlled thermostat attached to a pulley-driven mechanical water pump located on the front of the engine. The BMW N62 water pump pushes the coolant through a feed pipe to the rear of the engine block where it is drawn through the cylinder walls and heads and back to the thermostat housing. Cold coolant continues to circulate only through the engine block until the vehicle reaches operating temperature (85°C-110°C) - at operating temperature, the thermostat opens allowing hot coolant to circulate through the radiator.
The effects of a failed water pump are obvious - coolant is no longer circulated through the engine block causing immediate vehicle overheating and possible catastrophic engine damage. One of the main causes of water pump failure in the N62 V8 engine is simply due to age. The mechanical N62 water pump has a definitive lifespan and eventually will wear out. The BMW Repair Guide recommends replacing your N62 V8 water pump every 100,000 miles. Water pumps are also prone to coolant leaks around their gaskets. Heat and age cause the water pump gaskets to become brittle, allowing coolant to seep down the front of the engine creating a puddle under the front of the vehicle. If you suspect your water pump is leaking, it is best to go ahead and replace the entire unit.
The BMW Repair Guide strongly recommends also replacing the thermostat when performing a BMW N62 water pump replacement.
A BMW N62 water pump replacement is fairly straightforward except for one issue - the water pump's lower mounting bolt is located behind the harmonic balancer pulley. You must unfortunately remove the harmonic balancer pulley in order to access and remove this bolt. Although it is not technically challenging to remove the harmonic balancer pulley, it does require jacking up the front of the vehicle so the AC drive belt can be removed.
We give full step-by-step instructions below on how to perform a BMW N62 water pump replacement, along with a detailed parts list for your convenience. Please remember that you will lose approximately one gallon of engine coolant during this repair.
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This is the same factory thermostat that would be installed at the BMW dealership
Section 1 - Removing the BMW N62 Water Pump.
As discussed above, removing the BMW N62 water pump is fairly straightforward with one caveat - the harmonic balancer pulley must be removed to access the lower water pump mounting bolt. In most cases this will require jacking up the front of the vehicle so the AC drive belt can be removed (all drive belts must be loosened for this repair).
Unsnap the intake muffler lid. Loosen the hose clamp on the intake boot where it attaches to the throttle body. Grasp the lid and the boot and remove them from the vehicle.
Locate the thermostat on the front of the engine and unplug its heating element.
Locate the water pump and unplug the coolant temperature sensor.
Position a large drain pan under the vehicle. You will lose about 1/2 gallon of coolant when you remove the thermostat.
Using a small flat blade screwdriver, lift the metal locking clip on the radiator coolant return hose and pull it free from the thermostat.
Remove the secondary air pump pressure hose clamp from the top of the thermostat. This will make removing the thermostat much easier.
Use a small flat blade screwdriver or metal pick to lift the locking clip on the radiator coolant return hose where it attached to the water pump. Grasp the return hose and pull it loose from the pump.
Next, the bolts on the water pump pulley need to be loosened (DO NOT remove them yet). You must loosen the bolts now with the main accessory belt still on to keep the pulley from spinning.
Locate the main accessory belt tensioner. Remove its dust cap with a flat blade screwdriver.
Use a T50 torx bit to retract the tensioner pulley by turning it clockwise. Grasp the accessory belt and pull it loose.
Finish removing the water pump pulley bolts. Remove the water pump pulley from the vehicle.
Use a flat blade screwdriver or metal pick to release the metal locking clip on the lower water pump/radiator return hose. Pull the hose free from the water pump.
We like to remove the thermostat before the water pump...this allows the cooling system to drain with less mess and provides more room to remove the "hard to reach" lower expansion tank return hose.
Use a 10mm socket wrench to remove the three thermostat mounting bolts. Grasp the thermostat and remove it from the vehicle. Let the system thoroughly drain before moving to the next step.
With the thermostat removed, you can now easily access the lower expansion tank return hose. Use a flat blade screwdriver or metal pick to release its locking clip. Pull the return hose free from the water pump.
Next, the five water pump mounting bolts must be removed. Start at the top of the engine and remove the four that can be reached. The final fifth bolt is behind the harmonic balancer pulley and cannot be reached until step 23 below.
With the top four bolts removed, move to the bottom of the vehicle and locate the AC drive belt. There are two versions of AC drive belts on the N62 V8 engine; the stretch style belt and those with a belt tensioner. Our 2005 645ci originally had a stretch belt, but we performed a belt tensioner retrofit to eliminate it some years back. We find stretch belts to be a pain...hence the reason we performed a retrofit. If you are interested in replacing your stretch belt with the easier best tensioner system, NOW is the time to do it! Please see our article BMW N62 AC Belt Tensioner Retrofit – Stretch Belt Delete – 8 cyl. for more information. [caption id="attachment_35620" align="alignnone" width="1000"] The AC drive belt on a 2005 645ci. Note that the original "stretch" style belt was retrofitted with a belt tensioner.[/caption]
Stretch belts - Use a stretch belt tool to remove the AC belt off of the AC compressor.
Belt tensioner - Locate the AC belt tensioner. Use a torx bit to turn the tensioner counter-clockwise until you can slip the belt off of the AC compressor pulley. Remove the belt from the ac compressor and the harmonic balancer pulley.
Next, the harmonic balancer pulley must be removed so the final water pump bolt can be accessed. The harmonic balancer is anchored to the engine's crankshaft with eight bolts. The easiest way to access these bolts is from the top of the engine. Use a T45 torx bit and a socket wrench to remove the eight bolts and remove the harmonic balancer pulley from the vehicle.
With the harmonic balancer pulley removed, the final water pump bolt can be removed.
Grasp the water pump and pull it loose from the engine. If it is stuck like ours was, use a long flat blade screw driver to gently pry it off as shown below.
Grasp the short coolant return pipe and remove it from the engine. This pipe should always be replaced when performing a BMW N62 water pump replacement.
Section 2 - Installing the New N62 Water Pump.
Installing the new N62 V8 water pump is very straightforward...it is simply the above steps in reverse without any special procedures. We do recommend adding a small amount of liquid dish detergent to the water pipe o-rings to help them slide into the water pump easier. NEVER USE petroleum-based oil or grease on the rubber o-rings (they can dame them and cause potential leaks). We have provided a handy checklist below with the installation steps and important torque values.
BMW N62 Water Pump Installation Checklist
***The following steps were performed on a 2005 BMW 645ci...other models may vary.
Install a new return coolant pipe. Apply a small amount of liquid dish detergent to its rubber o-rings if necessary to help it slide into place. DO NOT use petroleum based oils or grease.
Make sure there is a new rubber gasket installed in the new water pump.
Install the new water pump. make sure it is firmly seated on the coolant pipes.
Install the five water pump mounting bolts and torque to 10.5 Nm (7.75 ft-lb).
Reinstall the harmonic balancer pulley. Torque its eight mounting bolts to 25 Nm (18 ft-lb).
Reinstall the AC drive belt.
Install the lower expansion tank return hose. Make sure you hear it click into place on the water pump.
Reinstall the thermostat and torque its three mounting bolts to 10.5 Nm (7.75 ft-lb).
Reinstall the lower water pump/radiator return hose.
Install the water pump pulley. Hand tighten its four mounting bolts (they will be torqued after the main accessory belt is installed).
Reinstall the main accessory belt.
Torque the four water pump pulley bolts to 10.5 Nm (7.75 ft-lb).
Reattach the radiator coolant return hose to the top of the water pump.
Reinstall the secondary air pump pressure hose bracket to the top of the thermostat.
Reattach the radiator coolant return hose to the thermostat.
Plug the thermostat heating element back in.
Plug the water pump coolant temperature sensor back into the water pump.
Reinstall intake muffler lid. Make sure the intake boot hose clamp is secure.
Reconnect the vacuum line to the intake boot.
Plug the mass air flow sensor back in.
Replace the upper engine cover.
BMW N62 Water Pump Replacement Finished
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