This article gives detailed instructions on replacing the thermostat 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 thermostat replacement can help cure a rough cold engine idle and no interior cabin heat.
The N62 V8 engine was first introduced in 2002, and was the workhorse of all BMW eight cylinder models until 2010. The N62 was the direct successor to the M60/M62 V8 engine of the 1990’s and was recognized for its technological advancements that created better fuel economy, lower emissions and greater reliability.
One of the many enhancements incorporated into the New Generation (NG) series of N62 V8s was an advanced cross-flow coolant system that allowed the engine to reach its operating temperature much quicker after a “cold start”. An integral part of this new system is an electronically controlled map thermostat that dynamically opens and closes based on the actual needs of the engine.
The BMW N62 thermostat is simply an electronically controlled valve that controls the flow of coolant through the engine block. When the N62’s thermostat is closed, coolant is only allowed to recirculate through the engine block, allowing for faster warm ups and a smoother cold idling engine. When the N62 engine reaches operating temperature (approx. 85 ºC-110 ºC) the thermostat opens allowing coolant to flow to the radiator so the motor doesn’t overheat.
The BMW N62 thermostat is attached to the belt driven water pump housing on the front of the engine. Like all mechanical engine parts in your BMW, it has a definitive life span and will eventually fail (no part lasts forever). Since the thermostat in your N62 eight cylinder is map-controlled, it is susceptible to electronic failure simply from normal wear and age. Another common cause of thermostat failure is due to deposits and corrosion, usually from a coolant system that has not been properly maintained. The good news is two fold if you have a failing thermostat: 1) N62 thermostats are “fail safe”…they will always fail in the open position so the engine does not overheat and 2) replacing the thermostat is relatively simple…it is easily accessible on the front of the engine and you do not need to remove the water pump (or a significant amount of parts) to replace it.
The two classic symptoms that your BMW N62 thermostat has failed is a very rough idling cold engine and no interior cabin heat. Usually the big V8 engine will run smoothly once it reaches operating temperature with a faulty thermostat – until then there is a significant chance of the engine struggling when the accelerator pedal depressed or even stalling out. If you have determined your thermostat has failed, it is usually a good idea to let the vehicle’s engine warm up before taking it out on the road.
Replacing the thermostat in your N62 V8 engine is very straightforward and can be easily done by the home mechanic with average abilities. The thermostat can be unbolted from the water pump housing without having to remove the water pump itself. We give full step by step instructions below along with a parts list for your convenience.
1. Thermostat (OEM) (required) – The BMW N62 V8 thermostat comes self contained in its own housing with a replacement sealing gasket. Factory spec thermostats are preset to open when the engine temperature reaches 105º C…if you are interested in upgrading to a high performance 90° C thermostat, please see option 2 below. Always use a high quality thermostat from a reputable manufacturer to avoid premature failure.
2. Antifreeze/Coolant (required) – You will lose approximately 1/2 gallon of coolant during this repair. It is recommended that only Genuine BMW Antifreeze/Coolant mixed 50/50 with distilled water is used in your N62 8 cylinder engine.
3. Thermostat (Performance) (optional) – Factory OEM thermostats are programmed to open when the engine’s operating temperature reaches 105° C. A high performance 90° C thermostat opens sooner than an OEM promoting better cooling of your engine and greater performance. Please be aware before ordering that you may have to recalibrate your vehicle’s Engine Control Unit (ECU) to properly use this performance part. If you are uncomfortable with this, we suggest sticking with the OEM thermostat in option 1 above.
As discussed above, removing the thermostat from your N62 V8 engine is actually quite easy. It is conveniently located on the front of the engine and is easily accessed by removing just the intake boot. You will lose about 1/2 gallon of coolant during the removal process so have a drain pan ready under the engine. If your vehicle has a belly pan, you will need to jack up the front of the vehicle and remove that first before draining the coolant.
- Use a T27 torx bit to remove the upper engine cover.
- Unplug the mass air flow (MAF) sensor.
- Disconnect the vacuum line from the intake boot.
- 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.
- 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.
- Using a 10mm socket wrench, remove the three bolts anchoring the thermostat to the water pump. Make sure not to lose the secondary air pump presssure hose bracket attached to the top bolt (see below). Note that the rear one can be a challenge to get out…use patience when removing.
- Grasp the thermostat and pull it loose from the water pump. Be prepared to lose about 1/2 gallon of coolant when the thermostat is removed. Remove the thermostat from the vehicle.
Installing the new thermostat is very straightforward with no special procedures…it is simply the reverse of the above steps. Make sure that you install a fresh rubber gasket with the new thermostat. We provide a handy checklist below with the installation steps, along with important torque values for your convenience. When you finish reinstalling your new thermostat, you must refill your system with coolant to replace the 1/2 gallon that was lost during the repair. Please see the checklist below for instructions on properly refilling your coolant.
BMW N62 Thermostat Reinstallation Checklist
- Install a new rubber gasket on the new thermostat.
- Carefully slide the new thermostat into the water pump.
- Install the three thermostat mounting bolts and hand tighten. Make sure the top bolt has the secondary air pump pressure hose bracket attached to it.
- Torque the three thermostat mounting bolts to 10.5 Nm (8 ft-lb).
- Replace the nut on the secondary air pump pressure hose bracket and tighten until snug.
- Replace the return coolant line on the thermostat. Make sure the locking clip is closed and you hear the hose “snap” onto the thermostat.
- Plug the thermostat sensor back in.
- Replace the intake muffler lid. Make sure the hose clamp is securely tightened.
- Replace the vacuum line on the intake boot.
- Plug the mass air flow sensor back in.
- Replace the engine cover.
- Refill coolant system as follows:
- 1. Only use Genuine BMW Antifreeze/Coolant mixed 50/50 with distilled water.
- 2. Remove the cap from the coolant expansion tank.
- 3. Turn the vehicle ignition on (do not start the vehicle). Set the driver’s side heat to high, the AC fan blower to low.
- 4. Start pouring coolant into the expansion tank until it is full.
- 5. Start the engine and top off the expansion tank until it is full. Replace the expansion tank cap and allow the engine to reach operating temperature (let it idle 15 minutes if cold).
- 6. Let engine completely cool. Check the coolant level and top off if necessary.