How to carry out replacement: Thermostat 300 SE, SEL (126.024, 126.025) Mercedes W126
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Change Mercedes W126 300 SE, SEL (126.024, 126.025) Thermostat yourself – manuals and video tutorials

How to change engine thermostat on MERCEDES-BENZ S-Class Saloon (W126) – replacement guide

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When to replace the Thermostat on your MERCEDES-BENZ S-CLASS
Recommended replacement interval for the part category Engine thermostat : 50000 km
Important!
This replacement procedure can be used for:
MERCEDES-BENZ S-Class Saloon (W126) 260 SE (126.020), MERCEDES-BENZ S-Class Saloon (W126) 260 SE (126.020), MERCEDES-BENZ S-Class Saloon (W126) 280 S (126.021), MERCEDES-BENZ S-Class Saloon (W126) 280 SE, SEL (126.022, 126.023), MERCEDES-BENZ S-Class Saloon (W126) 300 SE, SEL (126.024, 126.025) … View more

The steps may slightly vary depending on the car design.

This video shows the replacement procedure of a similar car part on another vehicle

All the parts you need to replace – Thermostat for S-Class Saloon (W126) and other MERCEDES-BENZ models
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Engine thermostat for S-Class Saloon (W126) Petrol (180 hp)
Tools
Replacement: engine thermostat – MERCEDES-BENZ S-CLASS (W126). Tools you might need:
Wire brush
All-purpose cleaning spray
Torque wrench
Combination spanner #10
Drive socket # 7
Drive socket # 8
Drive socket # 10
Ratchet wrench
Long nose pliers
Funnel
Fluid container
Fender cover
Buy tools
Replacement: engine thermostat – MERCEDES-BENZ S-CLASS (W126). AUTODOC recommends:
  • Check the condition of the coolant every time you replace the thermostat. Change the coolant if necessary.
  • Please note: all work on the car – MERCEDES-BENZ S-CLASS (W126) – should be done with the engine switched off.
Carry out replacement in the following order:
  1. Step 1
    Open the bonnet.
    Step 2
    Use a fender protection cover to prevent damaging paintwork and plastic parts of the car.
    Step 3
    Unscrew the coolant reservoir cap.
    Step 4
    Lift the car using a jack or place it over an inspection pit.
    Step 5
    Prepare a container for fluids.
    Step 6
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    Open the coolant drain tap.
  2. Step 7
    How to replace MERCEDES-BENZ S-Class Saloon (W126) 300 SE, SEL (126.024, 126.025) 1980 Thermostat - step-by-step manuals and video guides
    Drain the coolant from the engine.
    Replacement: engine thermostat – MERCEDES-BENZ S-CLASS (W126). AUTODOC experts recommend:
    All work should be done with the engine stopped.Wait until the coolant has completely flowed out of the drain hole.
  3. Step 8
    Close the coolant drain tap.
    Step 9
    Mercedes W126 280 SE, SEL (126.022, 126.023) 1981 Thermostat replacement: free workshop manuals
    Loosen the clamp of the expansion tank hose. Use a drive socket #7. Use a ratchet wrench.
  4. Step 10
    Changing Thermostat on MERCEDES-BENZ S-Class Saloon (W126) 380 SE, SEL (126.032) 1982 by yourself
    Detach the expansion tank hose from the thermostat housing.
  5. Step 11
    How to remove MERCEDES-BENZ S-CLASS 260 SE (126.020) 1983 Thermostat - online easy-to-follow instructions
    Detach the coolant hose.
  6. Step 12
    How to replace Thermostat on MERCEDES-BENZ S-Class Saloon (W126) 1984: download PDF manuals and video instructions
    Unscrew the thermostat housing fasteners. Use a drive socket #10. Use a ratchet wrench.
  7. Step 13
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    Remove the fastening bolts.
  8. Step 14
    Need to know how to renew Thermostat on MERCEDES-BENZ S-CLASS 1986? This free workshop manual will help you to do it yourself
    Remove the thermostat together with the housing.
    Replacement: engine thermostat – MERCEDES-BENZ S-CLASS (W126). Professionals recommend:
    Caution! Coolant may leak out of the coolant lines and thermostat housing.
  9. Step 15
    Changing of Thermostat on Mercedes W126 1987 won't be an issue if you follow this illustrated step-by-step guide
    Clean the thermostat housing mounting seat. Use all-purpose cleaning spray.
  10. Step 16
    Clean the thermostat mounting seat. Use a wire brush. Use all-purpose cleaning spray.
    Step 17
    MERCEDES-BENZ S-CLASS 300 SE, SEL (126.024, 126.025) Thermostat replacement: online guides and video tutorials
    Install a new thermostat.
  11. Step 18
    Replacing Thermostat on Mercedes W126 1989 300 SE, SEL (126.024, 126.025) by yourself
    Install the thermostat housing.
    Replacement: engine thermostat – MERCEDES-BENZ S-CLASS (W126). Tip from AUTODOC experts:
    Be sure to use a new O-ring when installing the sensor.
  12. Step 19
    S-Class Saloon (W126) 260 SE (126.020) 1990 Thermostat DIY replacement workshop manual
    Install the fastening bolts.
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