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Thermostat Replacement
 
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Pelican Technical Article:

Thermostat Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$100

Talent:

****

Tools:

Set of sockets, wrenches, screwdrivers

Applicable Models:

BMW Z3 (1996-02)

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 Z3 cooling system components include:

  • Radiator and coolant overflow tank.
  • Belt driven coolant pump bolted to the front of the engine block.
  • Belt driven fan attached to front of coolant pump. Viscous clutch controls fan speed based on engine temperature and rpms.
  • Electric (auxiliary) cooling fan attached to front of radiator. The cooling fan is controlled by the engine control module (ECM) via an output final stage.
  • Electrically heated thermostat.
  • Automatic transmission cooler or heat exchanger (if equipped).
  • 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 hoses and lines.

BMW Z3 models utilize two styles of thermostat depending on the engine. The thermostat is integrated with the thermostat housing; the two are replaced as a unit. It is mounted to the cylinder head at the front of the engine. 

4-cylinder models utilize a mechanical thermostat. 

6-cylinder models utilize an electrically heated engine thermostat. The engine control module (ECM) controls and monitors operation of the thermostat. If a fault occurs a code is stored in the ECM, usually with the description "Map cooling circuit". A fault code can be present yet the vehicle will lack any cooling system issues, such as overheating. If you have this fault code, replace your thermostat and bleed your cooling system. Other symptoms of a faulty thermostat are engine overheating, engine slow to warm up and lack of heat. 

Do not remove the expansion tank cap or work on any other part of the cooling system while the engine is hot. Coolant or hot steam may escape and will scald you. To do any work on the cooling system, wait until the engine has cooled off.

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

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.

Models with 4-cylinder engine: 
When replacing the thermostat, I suggest replacing both coolant hoses (green arrows) that connect to it.
Figure 1

Models with 4-cylinder engine: When replacing the thermostat, I suggest replacing both coolant hoses (green arrows) that connect to it. Many times I have replaced a thermostat, filled and bled the cooling system, only to find the hose is corroded and leaking.



Working at the sides of the thermostat, loosen hose clamps (green arrows).
Figure 2

Models with 4-cylinder engine: Working at the sides of the thermostat, loosen hose clamps (green arrows). Once loose, slide down hose away from thermostat.

With hose clamps moved, now you can remove the radiator hoses from the thermostat (green arrows).
Figure 3

Models with 4-cylinder engine: With hose clamps moved, now you can remove the radiator hoses from the thermostat (green arrows). Wiggle the hoses and pull them off the thermostat fittings.

Next you have to remove the four 10mm thermostat fasteners.
Figure 4

Models with 4-cylinder engine: Next you have to remove the four 10mm thermostat fasteners. (green arrows)

Remove thermostat from engine by pulling it away from engine.
Figure 5

Models with 4-cylinder engine: Remove thermostat from engine by pulling it away from engine. It may be stuck depending on how long it has been installed. If you have all the fasteners removed and it wonÂÂ't budge, tap it with a rubber mallet. Be prepared to catch dripping coolant, place a drain pan under the center of engine.

Using a plastic scraper, clean thermostat sealing surface.
Figure 6

Models with 4-cylinder engine: Using a plastic scraper, clean thermostat sealing surface. It is important not to use a metal scraper or razor blade here. You could damage sealing surface and thermostat seal will not seat properly, resulting in a leak. You can see my vehicle has quite a bit of corrosion (green arrow). I'ÂÂ'll need to clean all of this or the new thermostat wonÂÂ't seal. Once clean, confirm the sealing surface isn'ÂÂ't pitted. It if it, 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.


Install new thermostat and evenly tighten all fasteners. Install radiator hoses, and replace hose clamps. A small amount of new coolant can be used to lubricate the radiator hoses, this will make installing the hoses easier. Install fan shroud and fill and bleed cooling system. Remember to check cooling system for leaks and top up coolant when complete.

Models with 6-cylinder engine:
When replacing the thermostat (yellow arrow), I suggest replacing both coolant hoses(green arrows) that connect to it.
Figure 7

Models with 6-cylinder engine: When replacing the thermostat (yellow arrow), I suggest replacing both coolant hoses(green arrows) that connect to it. Many times I have replaced a thermostat, filled and bled the cooling system, only to find an O-ring on one of the coolant hoses has failed and leaks.



Working at the top of thermostat, locate the thermostat electrical connector.
Figure 8

Models with 6-cylinder engine: Working at the top of thermostat, locate the thermostat electrical connector. (green arrow)

Press the thermostat electrical connector wire retaining clip and remove electrical connector from thermostat by pulling straight off.
Figure 9

Models with 6-cylinder engine: Press the thermostat electrical connector wire retaining clip and remove electrical connector from thermostat by pulling straight off.

Working at both radiator hoses, use a flathead screwdriver to lever out the coolant hose retaining clips (yellow arrow).
Figure 10

Models with 6-cylinder engine: Working at both radiator hoses, use a flathead screwdriver to lever out the coolant hose retaining clips (yellow arrow).

Be sure to pull retaining clips out until they rest at the stop.
Figure 11

Models with 6-cylinder engine: Be sure to pull retaining clips out until they rest at the stop.

Next, remove coolant hoses from thermostat.
Figure 12

Models with 6-cylinder engine: Next, remove coolant hoses from thermostat. This can be tricky. The hoses have been attached to the thermostat for quite a while and may not come off easily. You will want to pull the hose off, while rocking it back and forth. Be careful not to damage the hose if you plan to reuse it. Once the hose moves off thermostat slightly, you can use a flathead screwdriver to gently lever the hose off while pulling. Now be very careful with this technique as everything you are prying on is made of plastic and can break.

Then, remove the 11mm engine lifting eye nut (green arrow).
Figure 13

Models with 6-cylinder engine: Then, remove the 11mm engine lifting eye nut (green arrow). This will help with removing thermostat

Remove two 13mm upper thermostat mounting fasteners.
Figure 14

Models with 6-cylinder engine: Remove two 13mm upper thermostat mounting fasteners. (yellow arrows)

Remove two 13mm lower thermostat mounting fasteners.
Figure 15

Models with 6-cylinder engine: Remove two 13mm lower thermostat mounting fasteners. (yellow arrows)


Remove the thermostat from engine. Be prepared to catch dripping coolant in a drain pan.

Using a plastic scraper, clean thermostat sealing surface.
Figure 16

Models with 6-cylinder engine: Using a plastic scraper, clean thermostat sealing surface. It is important not to use a metal scraper or razor blade here. You could damage sealing surface and thermostat seal will not seat properly, resulting in a leak. Once clean, confirm the sealing surface isnÂÂ't pitted. It if it, 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.


Install new thermostat and evenly tighten all fasteners. Install engine lifting eye nut and tighten. Install coolant hoses, listen for an audible click to confirm clips have engaged. A small amount of new coolant can be used to lubricate coolant hose O-rings, this will make installing hose easier. Connect thermostat electrical connector. Install fan shroud and fill and bleed cooling system. Remember to check cooling system for leaks and top up coolant when complete.

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Page last updated: Fri 12/9/2016 02:07:11 AM