Thermostat
Last Updated: 30-12-02

Figure 1	Figure 2

The thermostat controls the flow of coolant around the engine. It has a round plate which opens and closes acting as a valve which allows more coolant through the higher the engine temperature gets. Every thermostat has a rating in 'C, e.g a Calibra or Cavalier turbo thermostat is rated to 82'C. At this rating the thermostat opens fully and the engine gets maximum coolant flow.
Without the thermostat to control things the car would either not warm up, or overheat. If your car isnt warming up properly then there's a chance its the thermostat, and it has stuck open.
On the XE engine it is a very easy fit.

Figure 1 shows where the thermostat is located in the engine -marked in the red ring.
Figure 2 shows the old thermostat, which looks as old as the car - nasty. I noticed the new one had a beefier spring so at first thought it might not be the right one. However, it appears it is the same one and has simply been uprated, which is always nice.

When my GTE's thermostat stuck open, I considered a cooler thermostat (with a lower temp rating) from a Cav turbo. This would have meant the engine ran a little cooler and was less likely to reach the temperatures where the engine becomes sluggish. In the end I decided that based on my regular short journeys I would get the standard one to allow the car to warm up as quickly as possible.
I wouldnt bother with a warmer one, performance in the summer might be hampered or even worse the car could overheat.
Note: The thermostat is completely separate to the fan switch, both devices should be checked independantly

Fitting:

You will need: new thermostat, rubber ring (cost approx. £22 from Vauxhall), tools - obviously

1) For safety, disconnect the battery

2) The thermostat is part of the cooling system, so first of all the coolant needs to be drained. Locate the radiator bottom hose. Standing in front of the car, this is on your right near the bottom. With the car on the ground, undo the powersteering reservoir clamp and move the reservoir to one side for extra access.

3) Place a container (needs to have a volume of at least a few litres) under where the hose meets the radiator union. If the coolant is clean and fairly new then it can be reused.

4) The hose clip on the bottom coolant hose can now be loosened. Note, coolant will start to seep out. The hose takes a lot of 'persuasion' to wiggle it off. This is why it helps to move the powersteering reservior out the way, it took me both hands to rip the hose off. With the hose off the coolant will gush out and will soon be completely drained.

5) At the other end of the radiator is the thermostat and the thick top hose that connects it to the radiator. Using a screwdriver or a small size socket remove the 2 hose clips from each end of the hose.

6) You can now remove the old thermostat. Use a socket to undo the 3 bolts that secure it in place. The thermostat has a rubber seal between it and the head, and is clamped down tight, so you might need a large wrench of your choosing to loosen it for removal. I found that once I had rotated it 20' or so it came free.

7) Remove any bits of debris from the area and push the new rubber sealing ring onto the new thermostat. Fit the thermostat in the same place, and line up the bolt holes.

8) As Haynes would say - refit is the reverse of removal. The coolant can be reused if it is clean and fairly new.

9) Start the engine checking for leaks around the thermostat and bottom hose. Run the car, making sure it warms up nicely - job jobbed.

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