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Replacing Your Thermostat
 
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Pelican Technical Article:

Replacing Your Thermostat

Tom Morr

Time:

1 hour1 hr

Tab:

$25

Talent:

**

Tools:

8mm, 10mm socket, Flathead screwdriver

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

Parts Required:

Thermostat, gasket

Hot Tip:

Work on a cold engine

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.

The thermostat is located on the top of the water pump between the cylinder head and the power steering reservoir. 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 and should never be attempted. Coolant is also very toxic and 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.

If the coolant in the car is new there is no reason to replace it as long as you drain it into a clean container. Coolant is expensive and not great for the environment so if the coolant in your car is good, try and save it to reuse.

Begin by safely jacking up and supporting your car. With the car safely off the ground you will need to remove the engine tray. There are four 8mm bolts holding the tray on.

With the tray removed you will see radiator drain plug on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screwdriver to open the drain plug. The fluid drains out a small spigot facing rearward and not through the red plug. If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier. You do not need to drain all the coolant from the car, but just enough to get below the lower hose connection on the tank. If you are going to flush or replace the coolant, drain completely.

Working from the top of the car, you will need to remove the front engine cover. It simply pulls straight up off the engine.

Next remove the hose connected to the overflow tank and the radiator. If coolant comes out of either of these hoses you have not drained enough from the radiator.

Use a 10mm socket and extension to remove the three bolts holding the thermostat to the housing.

Pull the thermostat directly up on off the housing. On this model of Mercedes the top part of the housing and the thermostat are one piece. You cannot replace just the thermostat and trying to separate them will ruin the part.

Make sure you remove the old gasket, as it has a tendency to stay stuck in the housing body. The inside of the house can get a little corrosion, which you should clean up before installing the new unit. Always install a new gasket, even if you are just inspecting and reusing the old thermostat.

Check all your hoses while performing this job and replace any that are old, getting hard or brittle or beginning to weep.

Installation is the reversal of removal. Don't forget to replace your coolant.

Begin by safely jacking up and supporting your car.
Figure 1

Begin by safely jacking up and supporting your car. With the car safely off the ground you will need to remove the engine tray. There are four 8mm bolts holding the tray on (red arrows).

With the tray removed you will see radiator drain plug (red arrow) on the lower left front of the car.
Figure 2

With the tray removed you will see radiator drain plug (red arrow) on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screw driver to open the drain plug. The fluid drains out a small spigot (red arrow) facing rearward and not through the red plug (yellow arrow)..

If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier.
Figure 3

If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier. You do not need to drain all the coolant from the car, but just enough to get below the lower hose connection on the tank. If you are going to flush or replace the coolant, drain completely.

Working from the top of the car, you will need to remove the front engine cover (yellow arrow).
Figure 4

Working from the top of the car, you will need to remove the front engine cover (yellow arrow). It simply pulls straight up off the engine.

Next remove the hose connected to the overflow tank (red arrow) and the radiator (yellow arrow).
Figure 5

Next remove the hose connected to the overflow tank (red arrow) and the radiator (yellow arrow). If coolant comes out of either of these hoses you have not drained enough from the radiator.

Use a 10mm socket and extension to remove the three bolts (yellow arrows) holding the thermostat to the housing.
Figure 6

Use a 10mm socket and extension to remove the three bolts (yellow arrows) holding the thermostat to the housing.

Pull the thermostat (yellow arrow) directly up on off the housing (red arrow).
Figure 7

Pull the thermostat (yellow arrow) directly up on off the housing (red arrow). On this model of Mercedes the top part of the housing and the thermostat are one piece. You cannot replace just the thermostat and trying to separate them will ruin the part.

Make sure you remove the old gasket (yellow arrow), as it has a tendency to stay stuck in the housing body.
Figure 8

Make sure you remove the old gasket (yellow arrow), as it has a tendency to stay stuck in the housing body. The inside of the house can get a little corrosion which you should clean up before installing the new unit. Always install a new gasket, even if you are just inspecting and reusing the old thermostat. Installation is reversal of removal. Don't forget to replace your coolant.

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Comments and Suggestions:
johne Comments: Do you think it might have been time to do this replacement
August 17, 2016
  Followup from the Pelican Staff: Depends on mileage and what issue you are having. - Nick at Pelican Parts  

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