Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Thermostat

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REMOVAL & INSTALLATION 4 and 5-Cylinder Engines



See Figures 1, 2, 3 and 4

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Fig. Fig. 1: Exploded view of the thermostat housing and related componentsV8 engines



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Fig. Fig. 2: To remove the thermostat, loosen the housing retaining bolts ...



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Fig. Fig. 3: ... then remove the thermostat housing



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Fig. Fig. 4: Remove the thermostat from the engine block and clean the old gasket from the mating surfaces [bu5]

The thermostat housing is a light metal casting attached directly to the cylinder head, except on the 190D where it is attached to the side of the water pump housing.

  1. Open the radiator cap and depressurize the system.
  2.  
  3. Open the radiator draincock and partially drain the coolant. Drain enough coolant to bring the coolant level below the level of the thermostat housing.
  4.  


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

  1. Remove the bolts on the thermostat housing cover and remove the cover.
  2.  
  3. Note the installation position of the thermostat and remove the thermostat.
  4.  
  5. Installation is the reverse of removal. Be sure that the thermostat is positioned with the ball valve at the highest point and that the bolts are tightened evenly against the seal. On the 190D, the recess in the thermostat casing should be located above the lug in the thermostat housing.
  6.  
  7. Refill the cooling system and check for leaks.
  8.  

V8 Engines

  1. Drain the coolant from the radiator and block.
  2.  


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

  1. Remove the air cleaner.
  2.  
  3. Disconnect the battery and remove the alternator. Usually this need not be done on V8 Engines.
  4.  
  5. Unscrew the housing cover on the side of the water pump and remove the thermostat. Note that the thermostat used on 4.5 liter V8 models differs from the one used on other models by a different positioning of the ball valve.
  6.  
  7. If a new thermostat is to be installed, always install a new sealing ring.
  8.  
  9. Installation is the reverse of removal. Be sure to tighten the screws on the housing cover evenly to prevent leaks. Refill the cooling system and check for leaks.
  10.  

6-Cylinder Engines

  1. Drain the coolant from the radiator.
  2.  


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

  1. Remove the vacuum pump and put the pump aside.
  2.  
  3. Remove the three bolts on the thermostat housing.
  4.  
  5. Remove the cover and the thermostat.
  6.  
  7. Installation is the reverse of removal. Install the thermostat so that the ball valve is at the highest point. Refill the cooling system.
  8.  

 
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