How to carry out replacement: Thermostat 240 D 2.4 (123.123) W123
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Change W123 240 D 2.4 (123.123) Thermostat yourself – manuals and video tutorials

How to change engine thermostat on MERCEDES-BENZ Saloon (W123) – replacement guide

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Download your free tutorial and fix MERCEDES-BENZ Saloon (W123) 200 D 2.0 (123.120) problems yourself Download for free 1.42 MB Thermostat for W123 Shop now
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When to replace the Thermostat on your MERCEDES-BENZ Baureihe 123
Recommended replacement interval for the part category Thermostat : 50000 km
Important!
This replacement procedure can be used for:
MERCEDES-BENZ Saloon (W123) 200 (123.020), MERCEDES-BENZ Saloon (W123) 200 (123.220), MERCEDES-BENZ Saloon (W123) 230 E (123.223), MERCEDES-BENZ Saloon (W123) 230 (123.023), MERCEDES-BENZ Saloon (W123) 250 (123.026), MERCEDES-BENZ Saloon (W123) 280 (123.030), MERCEDES-BENZ Saloon (W123) 280 E (123.033), MERCEDES-BENZ Saloon (W123) 250 (123.026) … 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 Saloon (W123) and other MERCEDES-BENZ models
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Tools
Replacement: engine thermostat – MERCEDES-BENZ Saloon (W123). 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 Saloon (W123). 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 Saloon (W123) – 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
    How to change Thermostat on W123 1976 - free PDF and video manuals
    Open the coolant drain tap.
  2. Step 7
    How to replace MERCEDES-BENZ Saloon (W123) 240 D 2.4 (123.123) 1977 Thermostat - step-by-step manuals and video guides
    Drain the coolant from the engine.
    Replacement: engine thermostat – MERCEDES-BENZ Saloon (W123). 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
    W123 300 D 3.0 (123.130) 1978 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 Saloon (W123) 200 2.0 (123.220) 1979 by yourself
    Detach the expansion tank hose from the thermostat housing.
  5. Step 11
    How to remove MERCEDES-BENZ Baureihe 123 200 D 2.0 1980 Thermostat - online easy-to-follow instructions
    Detach the coolant hose.
  6. Step 12
    How to replace Thermostat on MERCEDES-BENZ Saloon (W123) 1981: download PDF manuals and video instructions
    Unscrew the thermostat housing fasteners. Use a drive socket #10. Use a ratchet wrench.
  7. Step 13
    How hard is it to do yourself: Thermostat replacement on W123 280 E 2.8 (123.033) 1982 - download illustrated guide
    Remove the fastening bolts.
  8. Step 14
    Need to know how to renew Thermostat on MERCEDES-BENZ Baureihe 123 1983? This free workshop manual will help you to do it yourself
    Remove the thermostat together with the housing.
    Replacement: engine thermostat – MERCEDES-BENZ Saloon (W123). Professionals recommend:
    Caution! Coolant may leak out of the coolant lines and thermostat housing.
  9. Step 15
    Changing of Thermostat on W123 1984 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 Baureihe 123 240 D 2.4 (123.123) Thermostat replacement: online guides and video tutorials
    Install a new thermostat.
  11. Step 18
    Replacing Thermostat on W123 1976 240 D 2.4 (123.123) by yourself
    Install the thermostat housing.
    Replacement: engine thermostat – MERCEDES-BENZ Saloon (W123). Tip from AUTODOC experts:
    Be sure to use a new O-ring when installing the sensor.
  12. Step 19
    Saloon (W123) 200 D 2.0 1977 Thermostat DIY replacement workshop manual
    Install the fastening bolts.
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