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Thermostat Replacement
 
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Pelican Technical Article:

Thermostat Replacement

Jared Fenton

Time:

6 hours6 hrs

Tab:

$75

Talent:

*****

Tools:

Torx driver set, screwdrivers, electric pump, vacuum coolant bleeder

Applicable Models:

Porsche 955 Cayenne S (2003-08)
Porsche 955 Cayenne Turbo (2003-08)

Parts Required:

New thermostat, coolant

Hot Tip:

Disconnect the battery before you do anything.

Performance Gain:

Better engine cooling.

Complementary Modification:

Replace water pump

The thermostat is used to restrict coolant flow in the engine. Once the temperature of the coolant reaches a certain temperature, the thermostat opens and allows the coolant to circulate unimpeded through the radiator. This allows quick warm up times. If the thermostat is stuck closed, the engine will overheat, as it will not allow coolant to circulate through the radiator.

Replacing the thermostat is a bit of a chore as it involves removing the intake manifold. Please refer to our article on Intake Manifold removal for more information.

Note to those with Cayennes that still have the original plastic coolant tubes.. You will need to update the coolant lines to the later metal style tubes. This is due to the construction of the tubes, you'll destroy them as you remove them.

Shown here is the starting point for replacing the thermostat.
Figure 1

Shown here is the starting point for replacing the thermostat. Please refer to our article on Intake Manifold removal for more info.

Since we will be working around the starter, it's a good idea to disconnect the negative lead from the chassis.
Figure 2

Since we will be working around the starter, it's a good idea to disconnect the negative lead from the chassis. The disconnect point is located under the driver's side carpet, near the seat. You'll see a slit in the carpet, pull it up and you'll see the 13mm acorn nut holding the ground lead to the frame (green arrow). Remove the nut and pull the lead up off the post.

I like to pull the ground lead up through the slit in the carpet to prevent the cable from touching any bare metal.
Figure 3

I like to pull the ground lead up through the slit in the carpet to prevent the cable from touching any bare metal.

Move to the wiring harness holder directly above the water pump at the front of the engine (green arrow).
Figure 4

Move to the wiring harness holder directly above the water pump at the front of the engine (green arrow). Pull the holder up and off the water pump. This will allow you to access the hose clamps for the upper radiator hoses.

Loosen and slide back the hose clamps on each upper radiator hose (green arrows).
Figure 5

Loosen and slide back the hose clamps on each upper radiator hose (green arrows).

Use a screwdriver to carefully pull each radiator hose up enough to slip the hose from the pump inside and push it down as far as possible.
Figure 6

Use a screwdriver to carefully pull each radiator hose up enough to slip the hose from the pump inside and push it down as far as possible. The idea here is to get as much coolant out of the engine as you can.

Now remove each radiator hose and stick the hose down into the thermostat housing.
Figure 7

Now remove each radiator hose and stick the hose down into the thermostat housing. Note that these steps may take some time depending on the strength of the pump.

Now we can begin removing the pump.
Figure 8

Now we can begin removing the pump. With the serpentine belt in place, loosen and remove the three T40 Torx bolts (green arrows) holding the water pump pulley to the pump.

Release tension on the serpentine belt and pull the belt up and over the front of the pulley (see our article on serpentine belt replacement for more information).
Figure 9

Release tension on the serpentine belt and pull the belt up and over the front of the pulley (see our article on serpentine belt replacement for more information).Once thee belt is removed, use a screwdriver behind the pulley (green arrow) to carefully pry the pulley off. Use caution as it is easy to damage the plastic pulley. You will now have access to remove the metal water line going to the thermostat housing.

On the left front cylinder head assembly, Loosen and remove the T30 Torx screw holding the dipstick to the engine and also the T30 Torx screw holding the metal water line in place (green arrows).
Figure 10

On the left front cylinder head assembly, Loosen and remove the T30 Torx screw holding the dipstick to the engine and also the T30 Torx screw holding the metal water line in place (green arrows). Pull the dipstick back about an inch and slide the metal water hose out from behind the plastic cable holder.

You'll now need to remove the T30 Torx screw holding the metal water line to the thermostat housing (yellow arrow).
Figure 11

You'll now need to remove the T30 Torx screw holding the metal water line to the thermostat housing (yellow arrow). Also remove the air hose connectors on each side (blue arrows). These are a bit tricky to get off. You'll need to carefully squeeze the upper and lower tabs for the catch to clear the groove on each cylinder head. If you manage to break the hoses which is very common, the new air hose is part number 948-106-016-03. Now remove the E10 bolts around the perimeter of the thermostat housing (green arrows). You'll also need to remove the metal water line to the housing.

You will now be able to access the E10 Torx bolt under the metal water line (green arrow).
Figure 12

You will now be able to access the E10 Torx bolt under the metal water line (green arrow). Be sure to also pry out the O-ring inside the thermostat housing and replace it (yellow arrow).

We will now need to remove the connections holding the rear coolant tubes to the engine.
Figure 13

We will now need to remove the connections holding the rear coolant tubes to the engine. Begin by pulling the wiring harness holding pins out of the holes on the plastic bracket (yellow arrows). Next, remove the three E10 Torx bolts holding the two halves of the bracket together (green arrows). Once the upper bracket is free, open the two plastic clips on top (blue arrows) and remove the other wiring harness.

Now loosen the hose clamps holding the water lines to the coolant tubes (green arrows).
Figure 14

Now loosen the hose clamps holding the water lines to the coolant tubes (green arrows). Carefully pull each coolant hose off and lift the thermostat housing and coolant tubes out as a unit. Also note the air line connection at the end of the bracket (yellow arrow). You'll need to be careful when moving this hose as it's very easy to break.

Shown here is the thermostat housing and coolant tubes removed from the engine.
Figure 15

Shown here is the thermostat housing and coolant tubes removed from the engine. The thermostat is located underneath as shown here (green arrow).

Remove the thermostat from the housing by placing the housing in a vise and press down on the securing plate while also turning the plate (green arrows).
Figure 16

Remove the thermostat from the housing by placing the housing in a vise and press down on the securing plate while also turning the plate (green arrows). Keep in mind that the thermostat spring exerts a lot of force on the securing plate. It will take some effort to move the plate. Once free, install the new thermostat in the same manner.

Now remove the outer metal gasket (green arrow) and carefully pry out the inner rubber gasket.
Figure 17

Now remove the outer metal gasket (green arrow) and carefully pry out the inner rubber gasket. Replace both of these gaskets with new ones. It's also a good idea to clean out the inside of the thermostat housing if any dirt or contaminants are sitting at the bottom. You're now ready to reinstall the housing.

Once the pump is installed, reattach the radiator hoses.
Figure 18

Once the pump is installed, reattach the radiator hoses. You will now need to bleed the cooling system of air. This is done by using a vacuum siphon type attachment such as Airlift. The idea here is to draw a vacuum in the cooling system, then use the vacuum to draw the new coolant into the engine. Follow the manufacturers instructions for each type of bleeder.

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Comments and Suggestions:
Ryan Comments: Have you had any experience replacing the thermostat housing on the V6 2004? It's in a different location.
May 3, 2016
  Followup from the Pelican Staff: The hoses and housing has to be removed from below the engine.

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
 
Richard Comments: What is the torque values for the eight bolts on top of the thermostat housing
December 4, 2014
  Followup from the Pelican Staff: I don't have those torque specs handy.

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
 
Every Man Comments: Furthering the above comment on vacuum hoses cracking; If they do crack, what is the appropriate step to address? Would a new hose need to be purchased and installed?
November 25, 2014
  Followup from the Pelican Staff: If the hoses crack, I would replace them. New hoses are your best bet. - Nick at Pelican Parts  
Andrew Dickens Comments: I have just done this job on my 2008 S. Your DIY was very helpful, but I found it was possible to change the thermostat with a lot less work. I only drained the coolant by pulling one end of a low hose off, then removed the intake manifold and water pump and pulled the thermostat out of the housing while it was still on the engine. I didn't need to touch the coolant pipes, dipstick or upper hoses. I did find that a number of the intake manifold vacuum hoses were extremely brittle and cracked with a very small amount of force. They would take no bending at all.
May 11, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 

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