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Pelican Technical Article:

Thermostat Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$100 to $180

Talent:

**

Tools:

17mm socket, E12, E10 Torx socket, flathead screwdriver, floor jack, jack stands, wheel chocks, safety glasses, torque wrench

Applicable Models:

Mercedes-Benz C350 (2007-14)
Mercedes-Benz CLK350 (2006-09)
Mercedes-Benz E350 (2006-14)
Mercedes-Benz GLK350 (2010-12)
Mercedes-Benz ML350 (2006-14)
Mercedes-Benz R350 (2006-12)
Mercedes-Benz S350 (2006, 2012-13)
Mercedes-Benz SLK350 (2005-14)

Parts Required:

Thermostat

Hot Tip:

Work on a cool car

Performance Gain:

Proper operating temperature

Complementary Modification:

Flush the radiator

The thermostat helps control the engine's 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 that 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.

Coolants last a much longer time than they did in the past so if your coolant is still good there is no need to dispose of it. Drain it into a clean container, and you can reuse it. If your coolant is old this is a great time to drain and flush the complete system. Please see our article on coolant drain and flush for additional assistance with that project.

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the coolant hoses so please see our article on engine cover removal for additional assistance.
Figure 1

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the coolant hoses so please see our article on engine cover removal for additional assistance.

Next, you need to remove the under body trays and drain the radiator (red arrow).
Figure 2

Next, you need to remove the under body trays and drain the radiator (red arrow). Please see our article on these procedures for further assistance.

The thermostat is one of the high points in the system (red arrow) so lots of people try and change it out without draining the coolant completely and then just topping up and bleeding the system after they are finished.
Figure 3

The thermostat is one of the high points in the system (red arrow) so lots of people try and change it out without draining the coolant completely and then just topping up and bleeding the system after they are finished. If you go this route please make sure to properly catch and dispose of the coolant that will come out when you release the thermostat hose.

You need to remove the drive belt to remove the thermostat; use a 17mm socket and turn the tensioner counter clockwise until the belt is loose and slip the belt off (red arrow).
Figure 4

You need to remove the drive belt to remove the thermostat; use a 17mm socket and turn the tensioner counter clockwise until the belt is loose and slip the belt off (red arrow). If you have further questions please see our article on drive belt replacement.

Use a flathead screwdriver and release the quick release clip from the thermostat (red arrow).
Figure 5

Use a flathead screwdriver and release the quick release clip from the thermostat (red arrow).

Wiggle and pull the hose from the thermostat and be prepared for some coolant to spill out.
Figure 6

Wiggle and pull the hose from the thermostat and be prepared for some coolant to spill out.

Use an E10 socket and remove the single bolt and idler pulley below the thermostat (red arrow).
Figure 7

Use an E10 socket and remove the single bolt and idler pulley below the thermostat (red arrow).

Disconnect the sensor from the bottom of the thermostat housing (red arrow).
Figure 8

Disconnect the sensor from the bottom of the thermostat housing (red arrow).

There are two E10 bolts holding the thermostat to the block (red arrow).
Figure 9

There are two E10 bolts holding the thermostat to the block (red arrow). Remove these bolts.

The upper bolt can be difficult to access as the air pump settles over time.
Figure 10

The upper bolt can be difficult to access as the air pump settles over time. You may need to use a T25 Torx and loosen the mounts (red arrows) for the pump to give you room to get at the upper thermostat bolt.

With the bolts removed pull the thermostat from the block (red arrow).
Figure 11

With the bolts removed pull the thermostat from the block (red arrow). These can get stuck over time so you may want to give it a gentle tap with a rubber mallet to help free it up. Never pry anything between the mounting surfaces of the thermostat and block or hit it with a metal hammer.

You need to thoroughly clean the mounting surface before installing the new thermostat and gasket (red arrow).
Figure 12

You need to thoroughly clean the mounting surface before installing the new thermostat and gasket (red arrow). Use something soft, plastic or a Scotch-Brite pad to clean this area. Never use a razor or anything that could gouge the surface.

If you have removed the thermostat to perform another job and are going to reinstall it, you must use a new gasket (red arrow) and O-ring (yellow arrow).
Figure 13

If you have removed the thermostat to perform another job and are going to reinstall it, you must use a new gasket (red arrow) and O-ring (yellow arrow). Installation is the reverse of removal.

This image shows you the routing of the drive belt for reinstallation.
Figure 14

This image shows you the routing of the drive belt for reinstallation. You can see where it routes around the alternator (red arrow), the power steering pump (green arrow) and the A/C compressor (yellow arrow). Do not forget to fill, bleed or top up your coolant.




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Comments and Suggestions:
Tom Comments: what is proper torque for a 2010 mercedes e350 thermostat housing. Is it 10nm or 25nm?
October 27, 2016
  Followup from the Pelican Staff: I don’t have that info.




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
 

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