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N62 8-Cylinder Thermostat Replacement
 
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Pelican Technical Article:

N62 8-Cylinder Thermostat Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$100

Talent:

****

Tools:

Flathead screwdriver, 10mm socket, plastic scraper

Applicable Models:

BMW 545i Sedan (2004-05)
BMW 550i Sedan (2006-10)

Parts Required:

Thermostat, hoses, engine coolant

Hot Tip:

Work with a cool engine

Performance Gain:

Car will cool down again or restore function of heater

Complementary Modification:

Change radiator hoses.

BMW E60 models utilize an electrically heated engine thermostat. Other cooling system components consist of:

  • Radiator and coolant overflow tank.
  • M54 and 8-cylinder engines: Belt driven coolant pump bolted to the front of the engine block.
  • N52 and N54 engines: Electric coolant pump bolted to the right front of the engine block.
  • Electric cooling fan attached to rear of radiator. The cooling fan is controlled by the engine control module (ECM) via an output final stage.
  • Automatic transmission cooler (heat exchanger).
  • Heater valve and heater core (for climate control).
  • Coolant level sensor inside expansion tank.
  • Coolant temperature sensor at cylinder head.
  • Radiator outlet temperature sensor
  • Coolant hose and lines.

The ECM controls and monitors operation of the thermostat. Controlling the thermostat function according to a map allows the engine management system (DME) to raise engine operating temperature quickly and precisely to the optimal range and to maintain that temperature range for maximum efficiency and minimum emissions.

If a fault occurs in the thermostat, a fault code is stored in the ECM, usually with a description of the "Map cooling circuit". A fault code can be present yet the vehicle will lack any cooling system issues, such as overheating. This is because the thermostat has a fail-safe mechanical function as well. If you have this fault code, replace your thermostat and bleed your cooling system. Other symptoms of a faulty thermostat are engine overheating, slow to warm up and lack of heat.

When replacing the thermostat, be sure to inspect the condition of the radiator hoses and radiator hose O-rings. It is a 50/50 shot that the O-ring on an old hose will reseal when reinstalling. If it does not reseal, you will have a coolant leak. If within your budget, replace the radiator hoses at the same time.

In this article I will describe how to replace the thermostat in your 8-cylinder engine. Be sure to work with a cool engine and confirm that the cooling system lacks pressure before opening the cooling system.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Drain the cooling system. See our tech article on the Cooling System Draining and Filling.

Remove the cooling fan. See our tech article on Radiator Cooling Fan Replacing.

The thermostat is located at the front of the engine, just below the coolant pump (green arrow).
Figure 1

The thermostat is located at the front of the engine, just below the coolant pump (green arrow).

Working at the intake air duct, pull the vacuum line (green arrow) off the air duct.
Figure 2

Working at the intake air duct, pull the vacuum line (green arrow) off the air duct.

Using a flathead screwdriver, loosen both the intake air duct hose clamps (green arrows).
Figure 3

Using a flathead screwdriver, loosen both the intake air duct hose clamps (green arrows).

Once the clamps are loose, pull the air duct off the throttle housing.
Figure 4

Once the clamps are loose, pull the air duct off the throttle housing. Then pull it off the intake air box. Place the duct aside.

Working below the throttle housing, disconnect the thermostat electrical connector (green arrow) by pressing the wire release tab and pulling it off.
Figure 5

Working below the throttle housing, disconnect the thermostat electrical connector (green arrow) by pressing the wire release tab and pulling it off.

Working at the radiator hose connected to the thermostat, use a flathead screwdriver to lever out the coolant hose retaining clips (green arrow).
Figure 6

Working at the radiator hose connected to the thermostat, use a flathead screwdriver to lever out the coolant hose retaining clips (green arrow). Be sure to pull the retaining clips out until they rest at the stop (yellow arrow).

Next, remove the coolant hose from the thermostat.
Figure 7

Next, remove the coolant hose from the thermostat. This can be tricky. The hose has been attached to the thermostat for quite a while and may not come off easily. You will want to pull the hose off in the direction of the green arrow, while rocking it back and forth. Be careful not to damage the hose if you plan to reuse it. Once the hose moves off the thermostat slightly, you can use a flathead screwdriver to gently lever the hose off while pulling it. Be very careful with this technique as everything you are prying on is made of plastic and can break.

Now it is time to remove the thermostat fasteners.
Figure 8

Now it is time to remove the thermostat fasteners. There are three 10mm fasteners (green arrows) and a metal bracket (yellow arrow). First remove all three 10mm fasteners. Then move the metal bracket aside, leaving it attached to the pipe above the thermostat.

Remove the thermostat from the engine in the direction of the green arrow.
Figure 9

Remove the thermostat from the engine in the direction of the green arrow. Lift the metal bracket (blue arrow) up while pulling the thermostat off the coolant pump. Be prepared to catch dripping coolant in a drain pan. Using a plastic scraper, clean the thermostat-sealing surface. It is important not to use a metal scraper or razor blade here. You could damage the sealing surface and the thermostat seal will not seat properly, resulting in a leak. Once clean, confirm the sealing surface isn't pitted. If it is, it may not seal correctly. You may have to add some epoxy and sand it down to get a smooth and even sealing surface, I see this happen more on older BMWs. You can see our subject vehicle has quite a bit of corrosion on the sealing O-ring. Install a new thermostat and evenly tighten all the fasteners. Install the coolant hose. Listen for an audible click to confirm the clip has engaged. A small amount of new coolant can be used to lubricate the coolant hose O-ring. This will make installing the hose easier. Connect the thermostat electrical connector. Install the cooling fan and fill and bleed the cooling system. Remember to check the cooling system for leaks and top up the coolant when the job is complete.


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Page last updated: Sat 12/3/2016 02:24:33 AM