BMW Coupes and Sedans 1970-1988 Repair Guide

Thermostat

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REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4

The thermostat is located near the water pump, either on the cylinder head, intake manifold or between 2 coolant hose sections. On the diesel engine, it is located directly above the water pump.

  1. Remove the fan to gain access. See the water pump removal procedure in this section for special procedures required to remove the fan.
  2.  
  3. Drain enough coolant out to lower the coolant level below the thermostat. If reusing the coolant, save it in a clean container before removing the thermostat.
  4.  



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Fig. Fig. 1: Loose and remove the thermostat housing retainer bolts ...



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Fig. Fig. 2: ... then remove the housing from the cylinder head



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Fig. Fig. 3: When you remove the thermostat, note the positioning for installation purposes



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Fig. Fig. 4: Remove the seal(s) from the thermostat and housing


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. On the M5, M6 engine, the forward (removable) portion of the thermostat housing has a hose connected to it. The hose need not be disconnected to remove the housing.
  2.  

On the 1983-87 3.2 and all 3.5 liter engines including diesel, there is a thermostat housing gasket, and also an inner rubber seal to keep the closed thermostat from leaking. On the engine used in the M5, M6, there is a large O-ring seal for the main portion of the housing and a small, O-ring located above in a small passage. Replaced the seal(s) whenever removing the thermostat.

Note that thermostats for 3.5L engines built in 1986-88 carry an A designation. This thermostat is a smaller in diameter.

On all models except the M3, the thermostat is installed with the thermostatic sensing unit facing inward and the cross-band facing outward.

  1. Remove the bolts securing the thermostat housing in place. Once removed, tap the housing lightly with the palm of your hand to break the seal.
  2.  
  3. Remove the thermostat and seal(s) from the housing. Remember the direction in which the thermostat faced.
  4.  
  5. Inspect the housing mating surface and remove any seals or gasket material which may be attached.
  6.  

No gasket material is needed to install the thermostat.

  1. Install the seal(s) around the thermostat and position in the housing.
  2.  
  3. Align the thermostat housing to the engine and secure with the retainer bolts. Tighten the bolts to 6-7 ft. lbs. (8-10 Nm).
  4.  
  5. Refill and bleed the cooling system.
  6.  

BLEEDING THE COOLING SYSTEM



With Bleeder Screw on Thermostat Housing

See Figures 5 and 6

Set the heat valve in the WARM position, start the engine and bring to normal operating temperature. Run the engine at fast idle and open the venting screw on the thermostat housing until the coolant comes out free of air bubbles. Close the bleeder screw and refill the cooling system.



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Fig. Fig. 5: Loosen the bleeder bolt until air comes out. NEVER remove the bolt entirely



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Fig. Fig. 6: Some bleeder screws are slotted

Without Bleeder Screw

Fill the cooling system, place the heater valve in the WARM position, close the pressure cap to the second (fully closed) position. Start the engine and bring to normal operating temperature. Carefully release the pressure cap to the first position and squeeze the upper and lower radiator hoses in a pumping action to allow trapped air to escape through the cap. Recheck the coolant level and close the pressure cap to its second position.