Changing thermostat

General

The thermostat is a valve that opens and closes based on a specific temperature.
Once it starts to open it will allow more engine coolant fluid to pass through it and into the cooling system.
This ensures an increased flow of engine coolant fluid in the cooling system as the temperature inside the engine increases.

The OEM thermostat starts to open at 78C (172F) and will be fully opened at 90C (194F).
With the OEM ECU the radiator fans are set to turn on at 91C (196F) but real life test have shown that they turn on at 97C (207F).

Normal operating temperatures

See: Engine coolant - Normal operating temperatures

Thermostat recommendations

See: Thermostat recommendations

Required tools

Ratchet
10mm ratchet socket
Several different ratchet extensions
Oil/Fluid catch pan
Towels
Floor jack + 2 jack stands

How to change the thermostat

Pre-conditions and jacking up the car

Make sure that the engine is cold. Never open the cooling system when the engine is hot.
Put the car in the first gear and set the parking brake.
Jack up the car on the front by using the central jacking point near the engine.
There are two front-jacking-points on each side. Place one jack stand on each side at the jacking-point that is the furthest away from the front wheel.
Lower and remove your floor jack (or keep it in place for extra safety)

Removing the thermostat

The workshop manual describes a relatively complicated way of removing the thermostat.
There is a much simpler way that let's us remove the the thermostat within 15 minutes. Only two bolts are required to be removed.

There are two thick black hoses connected to the radiator.
The lower radiator hose connects on one end to the radiator and on the other end to the engine.
You will need to remove the radiator hose from the engine as the thermostat sits between the hose and the engine.

Get under the car and search for the lower radiator hose that connects to the engine.
Follow the hose until the end point that connect to the engine.
The hose is hold in place with a clamp mounted on the thermostat cover.
There is no need to remove that clamp as we will remove the hose together with the thermostat cover.
The thermostat cover it mounted with 2x 10mm bolts onto the engine.
You should reach both bolts very easily from under the car.
Loosen the bolts but to not remove them completely yet.
As soon as you remove the thermostat cover, a significant amount of engine coolant fluid will leak out of it.
So make sure that your face is out of the way and that you have your oil/fluid catch pan placed below it.
Remove the two bolts completely and remove the thermostat cover slowly as the thermostat is hold in place only by the cover.
Once the thermostat cover is removed you should either have the thermostat already falling down or it might be still stuck on the engine or inside the thermostat cover.
Simply pull it off.
Clean the thermostat cover, engine port and the area around it.

Testing your thermostat

Before installing the new thermostat it might be a good idea to test if it actually works.
You can do this by putting it inside cooking pot with water. Heat the water until it starts to boil.
Optionally you can place a thermometer inside the pot to see at which temperature the thermostat starts to open and when it is fully opened.
You can also place your old and new thermostat together in the cooking pot to see the differences in realtime.

Installing the thermostat

The OEM thermostat comes with a gasket that you still have to attach to the thermostat.
On the thermostat you will see a marker saying "Up".
Additionally the gasket will have a notch.
Place the gasket on the thermostat so that the notch is where "Up" is located.
Then place the thermostat inside it's port on the engine.
There will be a notch inside the engine port. Make sure that the notch of the gasket sits inside the notch of the engine port.
Push the thermostat inside the engine port and make sure the gasket sits flush.
Normally the thermostat should now be held in place so that you can attach the thermostat cover again.
Tighten the two bolts of the thermostat cover.
Start the engine for 30 seconds and check the engine coolant fluid level afterwards.