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Pelican Technical Article:

Cooling Thermostat Removal

Kerry Jonsson

Time:

3 hours3 hrs

Tab:

$150

Talent:

****

Tools:

10mm socket w/swivel and ratchet, flat head screwdriver

Applicable Models:

Mercedes-Benz 500SL (1990-93)
Mercedes-Benz SL500 (1994-02)

Parts Required:

Engine coolant, thermostat, thermostat O-ring

Hot Tip:

Remove radiator cap and drain radiator before removing thermostat

Performance Gain:

Improve poor heating in winter and overheating in summer

Complementary Modification:

Flush cooling system when replacing thermostat

Although your engine starts when it's cold it is still not running efficiently. When an engine is cold pistons, rings and cylinder sleeves have not expanded to improve sealing. An engineer designs and engine to work most efficiently within a certain temperature range. A difficult task since they don't know if the car is in Alaska or Florida. This is the main reason we have engine thermostats. An engine thermostats job is to restrict cooling flow to the engine until enough heat is generated by the combustion process and then open when the engine reaches operating temperature. If the engine cools off a little the thermostat should start to close to restrict flow and keep the temperature up. If you stuck in traffic the thermostat should be wide open for maximum cooling. In this tech article we are going to go over all the steps to replace your thermostat.

We strongly recommend draining your cooling system before removing your thermostat. Just pulling off the thermostat radiator hose will easily cause a mess in your garage or driveway. See our tech article on draining, refilling and bleeding the cooling system. To do this you will need to remove the lower splash shield. See our tech article on removing the lower splash shield. We recommend you remove the cooling fan and shroud to gain clearer access to the thermostat. See our tech article on removing the coolant fan and shroud. We have also removed the accessory drive belt for photographic purposes but you do not have to. However removing the belt does give you easier access to the thermostat and hose and will make your life a lot easier.

The thermostat is mounted on the side of the water pump, not the top. If you have a 10mm swivel socket then you will not need to remove the coolant pump, if you do not you will need to remove the coolant pump. At this point we recommend you replace the coolant pump. See our tech article on removing the coolant pump.

You should drain your cooling system prior to opening it up to prevent a mess. You can access the radiator drain plug while the car is on the ground but if you want more room to work you should jack up and support the front of your vehicle. See our tech article on jacking up and supporting your vehicle.

This photo illustrates under the front of the car on the passenger side, looking at the front of the radiator.
Figure 1

This photo illustrates under the front of the car on the passenger side, looking at the front of the radiator. From the radiator drain the coolant from the radiator. See our tech article on draining, refilling and bleeding for further information.

Remove the cooling fan and shroud see our tech article on removing the cooling fan and shroud.
Figure 2

Remove the cooling fan and shroud see our tech article on removing the cooling fan and shroud.

Working at the front of the engine loosen the four 10mm fasteners (green arrows) that hold on the coolant pump pulley (green arrow) while the belt is still on the pulley.
Figure 3

Working at the front of the engine loosen the four 10mm fasteners (green arrows) that hold on the coolant pump pulley (green arrow) while the belt is still on the pulley. This will help you hold the pulley still. You can also use a screwdriver between two fasteners to hold the pulley in place while you loosen the fasteners.

Loosen the four 10mm fasteners that hold on the idler pulley (green arrows) while the belt is still on the pulley.
Figure 4

Loosen the four 10mm fasteners that hold on the idler pulley (green arrows) while the belt is still on the pulley. This will help you hold the pulley still. You can also use a screwdriver between two fasteners to hold the pulley in place while you loosen the fasteners.

Remove the accessory drive belt from the front of the engine.
Figure 5

Remove the accessory drive belt from the front of the engine. See our tech article on removing the accessory driver belt for further information. You can delay this step until you have loosened all the fasteners that hold down the pulleys.

Remove the cooling pump pulley by fully removing the four 10mm fasteners.
Figure 6

Remove the cooling pump pulley by fully removing the four 10mm fasteners. You can use a long screwdriver or strap wrench to hold the pulley in place while you loosen the fasteners. Position a screwdriver in the place of the red arrow between the fasteners to hold the pulley in place while you loosen any of the other fasteners. You should crack all four loose before fully removing the fasteners. Here we are also using the grip of the accessory drive belt to help hold the pulley still as well.

Remove the idler pulley by fully removing the four 10mm fasteners.
Figure 7

Remove the idler pulley by fully removing the four 10mm fasteners. Here we are using a screwdriver once again to hold the pulley still while we loosen the fasteners. Position the screwdriver in place of the red arrow and loosen one of the other fasteners. Here we are also using the grip of the accessory drive belt to help hold the pulley still. Once you have loosened the 4 fasteners one each pulley you can remove the accessory drive belt.

Loosen the upper hose clamp at attaches to the thermostat housing.
Figure 8

Loosen the upper hose clamp at attaches to the thermostat housing.

Loosen the lower hose clamp of the thermostat housing hose.
Figure 9

Loosen the lower hose clamp of the thermostat housing hose.

Use a long thin pry bar and position it in the inside curve of the hose.
Figure 10

Use a long thin pry bar and position it in the inside curve of the hose. Lever the pry bar in the direction of the blue arrow to remove the hose from the thermostat housing and the pipe passage. This hose is pliable enough to do this without damaging it. It is strongly recommend you replace the hose for this repair.

Remove the three 10mm fasteners (green arrows) that hold the thermostat housing to the water pump.
Figure 11

Remove the three 10mm fasteners (green arrows) that hold the thermostat housing to the water pump. As you can see some corrosion has built up in the thermostat housing and possibly restricting coolant flow.

Pull the thermostat element out of the water pump if corrosion is holding it in.
Figure 12

Pull the thermostat element out of the water pump if corrosion is holding it in. You can use a small pry bar to lever it out of the coolant pump housing. Notice the black O-ring seal around the thermostat (green arrow). Remember its location for installation. A new one should be provided with your thermostat. Installation is the reverse of the removal procedure. Fit the thermostat element into the coolant pump housing and mount the thermostat housing. Position the two hose clamps on the small thermostat housing hose, fit the hose between the thermostat housing and the pipe passage. Tighten the clamps. Attach both idler pulley, cooling pump pulley and tighten the fasteners. Fit the drive belt and set the tension of the belt. Install the cooling fan and shroud. Close the radiator coolant drain plug and fill the cooling system according to our tech article on draining, refilling and bleeding the cooling system. Start the engine to verify there are not coolant leaks and the engine does not overheat.

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Comments and Suggestions:
Rob Comments: Will this guide also work for a 93 400e? I can't find a guide for thermostat removal for a w124 with a M119 thermostat removal
November 18, 2016
  Followup from the Pelican Staff: no. Applicable Models:

Mercedes-Benz 500SL (1990-93)
Mercedes-Benz SL500 (1994-02)

We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.


I would grab a repair manual. It will have the procedure, special tools and torque specs.


Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Jack Comments: Talk to pars people they couldn't find it either so they suggested I talk to you , 1992 Mercedes 500SL
June 23, 2016
  Followup from the Pelican Staff: Ok. I am not the best with parts numbers, more of a technical guy.

From what I can see, if you need a bleeder for the housing, you have to buy a complete housing:

Part Number: 1192011030 - Nick at Pelican Parts
 
Jack Comments: Please help me find the following part- Bleeder Screw Housing, the no. on the housing is- R119 201 07 30
June 23, 2016
  Followup from the Pelican Staff: You didn't mention what vehicle it is from.

For an instant response, give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 

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Page last updated: Fri 12/9/2016 02:27:39 AM