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Pelican Technical Article:

Thermostat Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$3 to $35

Talent:

*

Tools:

10mm socket, flathead screwdriver

Applicable Models:

Mercedes-Benz 260E (1987-89)
Mercedes-Benz 300CE (1988-93)
Mercedes-Benz 300E (1986-93)
Mercedes-Benz 300TE (1988-92)
Mercedes-Benz E320 (1994-95)

Parts Required:

Thermostat, gasket

Hot Tip:

Work on a cold cooling system

Performance Gain:

Engine runs at the proper temperature

Complementary Modification:

Replace older hoses

The thermostat helps control the engines temperature. If your car is running too hot and there is the proper amount of coolant in the car and it is not leaking, or your car is taking a long time to warm up, there is a very good chance your thermostat is bad and needs to be replaced.

If you are going to be working on the thermostat, make sure the car is cool and not under pressure. Working on a hot engine or one under pressure can cause serious harm (coolant is also very toxic) and should never be attempted. Coolant needs to be collected and disposed of in accordance with your local regulations. Pouring coolant down a drain or into the street is illegal. Also, be sure to wash your hands thoroughly after working around it. Check all your hoses while performing this job and replace any that are old, getting hard or brittle or beginning to weep.

The thermostat (red arrow) is located on the top of the water pump between the cylinder head (yellow arrow) and the power steering reservoir (green arrow).
Figure 1

The thermostat (red arrow) is located on the top of the water pump between the cylinder head (yellow arrow) and the power steering reservoir (green arrow).

Once the car is cold, begin by removing the cap on the coolant reservoir to release any residual pressure (red arrow).
Figure 2

Once the car is cold, begin by removing the cap on the coolant reservoir to release any residual pressure (red arrow).

Remove the clamp and large hose coming out of the top of the thermostat housing (red arrow).
Figure 3

Remove the clamp and large hose coming out of the top of the thermostat housing (red arrow).

There are three 10mm bolts holding the top of the thermostat to the housing.
Figure 4

There are three 10mm bolts holding the top of the thermostat to the housing. These can stick a little as coolant can get in them and corrode them. Remove the bolts and wiggle the top from the housing. Use care not to damage the thermostat switch beside the lid.

You can now separate the lid (red arrow) from the housing (yellow arrow), revealing the thermostat.
Figure 5

You can now separate the lid (red arrow) from the housing (yellow arrow), revealing the thermostat.

Pull the thermostat (red arrow) up and out of the housing (yellow arrow).
Figure 6

Pull the thermostat (red arrow) up and out of the housing (yellow arrow). You should clean the contact surfaces of the housing of any gunk or corrosion.

Always install a new seal or gasket (red arrow) even if you are reusing your thermostat.
Figure 7

Always install a new seal or gasket (red arrow) even if you are reusing your thermostat. Installation is the reverse of removal. Don't forget to replace any coolant you may have lost.





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Comments and Suggestions:
Kevin Comments: Thanks for the help Casey.
March 18, 2017
  Followup from the Pelican Staff: No problem! - Casey at Pelican Parts  
Kevin Comments: What if you are losing coolant?
March 17, 2017
  Followup from the Pelican Staff: You need to locate the source of the coolant loss. I would make sure there are no external leaks, no oil in coolant and vice versa, then perform a block test to see if you have combustion gasses present in the cooling system. If the test comes back positive then you have a head gasket, block or cylinder head issue. - Casey at Pelican Parts  
600Benz Comments: I Have 97 s320 & I Replaced Water pump & Thermostat & Still Overheating... Any Idea Why Still Overheating? I need Help. Tired Of Dealing With This Car.
December 12, 2016
  Followup from the Pelican Staff: I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts  
S T Choo Comments: My 280E1994 used to have an oil heater for use in the cooler climate area. Now that my car is used only in the hot Tropical area, my mechanic has removed the oil heater which he said is not required anymore. Only lately that I realised that whenever I start the car first time in the morning, the engine cooling fan starts to work straight away instead of waiting for the engine to get hot first. My question is why is the engine cooling fan runs straight away when I start the car and why the thermostat is not controlling the working of the of the fan? Could my thermostat b faulty? How do we know when to replace the thermostat?
September 21, 2016
  Followup from the Pelican Staff: The coolant temp sensor may be faulty. - Nick at Pelican Parts  

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Page last updated: Thu 6/29/2017 03:04:46 AM