Thermostat replacement

January 18, 2003

Reading time ~1 minute


  • temperature gauge not reading at 12 o’clock You will need ————-
  • a new thermostat and rubber o-ring
  • a 10mm socket
  • 32mm spanner for the viscous coupling on the fan
  • some antifreeze and deionized water, to refill the system

The new thermostat

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Thermostat housing

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Don’t do this with a hot engine.

Remove the fan and viscous coupling for easier access, although it’s possible to do the job without. If you have a 32mm thin spanner then you’ll probably want to remove it, if not then try and manage without!

Remove the 4 bolts holding the thermostat housing to the front of the engine. There are two short ones and two long ones. Ease the housing off the front of the engine (leave the hose attached). Coolant will flow out of the front of the engine when you do this.

The thermostat will probably be stuck in the housing, so remove it.

Put the replacement o-ring around the edge of the new thermostat and test-fit it in the housing. There should be an arrow or dot stamped in the perimeter of the thermostat, this should point upwards. I’ve read that it’s possible to install it in the wrong orientation such that you break it when you tighten the housing bolts. If you have a temperature regulation problem again in a week’s time, this might be what happened.

Put the thermostat (correctly oriented) in the hole in the front of the engine. Replace the thermostat housing and four bolts, then replace the fan.

Fill the header tank with coolant. There are two ways to bleed the system. In the first way, you loosen the bleed screw on the top of the thermostat housing and wait until there are no more bubbles coming out. The other way is to remove the small pipe from the top of the radiator, the one that goes to the header tank. Leave it off until there are no bubbles in the coolant coming out.

Go for a 15 minute drive and check the coolant level again (take some with you just in case). If your cooling system is working properly, the temperature gauge will read exactly 12 o’clock under virtually all circumstances.

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