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Coolant Temperature Sensor Replacement
 
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Pelican Technical Article:

Coolant Temperature Sensor Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$8 to $40

Talent:

**

Tools:

19mm wrench, rags

Applicable Models:

Mercedes-Benz 240D (1977-83)
Mercedes-Benz 300CD (1978-85)
Mercedes-Benz 300D (1977-85)
Mercedes-Benz 300TD (1979-85)

Parts Required:

Coolant temperature sensor

Hot Tip:

Make sure to install a new crush washer

Performance Gain:

Working temperature gauge

Complementary Modification:

Coolant flush

If your temperature gauge suddenly stops working there is a good chance that the sensor on the engine block has failed. The sensor is located on the left side of the block under the fuel injection lines and behind the glow plug.

Due to the placement of the sensor under the fuel lines I recommend draining the coolant to at least a level below the opening for the sensor. If you have really small hands you may be able to swap them out quickly but I recommend taking your time and cleaning up the mounting area. Please see our article on coolant flush and refill for additional assistance.

A couple of safety precautions/instructions you may want to observe before beginning:

Allow cooling system to cool down to a coolant temperature of less than 90 degrees C. Open the cap of cooling system slowly; turn a conventional coolant cap as far as the first detent and turn a screwed coolant cap approx. 1/2 turn and release the pressure. Wear protective gloves, protective clothing and eye protection. Always dispose of used coolant in accordance with the regulations in your region; NEVER pour coolant down a drain, on the ground or into a sewer.

Remember your car may have been serviced before and parts 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 working with the electrical system, disconnect the battery before beginning. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

The sensor is located on the left side of the block under the fuel injection lines and behind the glow plug (red arrow).
Figure 1

The sensor is located on the left side of the block under the fuel injection lines and behind the glow plug (red arrow).

The sensor is difficult to work on due to the hard metal fuel lines (red arrow).
Figure 2

The sensor is difficult to work on due to the hard metal fuel lines (red arrow).

Pull the electrical connection off the end of the sensor (red arrow).
Figure 3

Pull the electrical connection off the end of the sensor (red arrow).

Use a 19mm wrench and remove the sensor (red arrow).
Figure 4

Use a 19mm wrench and remove the sensor (red arrow).

While the sensor is out check the mounting surface and give it a cleaning.
Figure 5

While the sensor is out check the mounting surface and give it a cleaning. Make sure that the old crush washer is not stuck to the engine (red arrow).

This photo illustrates the old sensor and washer; always install a new washer with the sensor.
Figure 6

This photo illustrates the old sensor and washer; always install a new washer with the sensor. Installation is the reverse of removal. Do not forget to refill and bleed the coolant.

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Comments and Suggestions:
Rojo Comments: My normal operating temperature at idle and at highway speeds with RPM @ 2-3 I have an average of 82 degrees Celsius. The instant that I turn on my parking lights, headlights, turn signals, or any electrical draw my temp gauge drastically increases.
February 14, 2017
  Followup from the Pelican Staff: Could be a charging system issue? I would use an infrared thermometer to verify that the temp at the upper radiator hose is actually getting hotter. - Casey at Pelican Parts  
-Nate Comments: Why is the first photo of the Air conditioning receiver-dryer ? .

Makes no sense at all .

-Nate
May 16, 2016
  Followup from the Pelican Staff: The first photo is of the engine and the component location. Possible you commented on the wrong article? - Nick at Pelican Parts  

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Page last updated: Sun 4/23/2017 02:57:57 AM