Removing & replacing a thermostat

Part 1. Preparation and safety

Objective

• Safely remove and replace a cooling system thermostat.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• Coolant in the cooling system could be above its boiling point. Never open a radiator cap fully until ALL pressure has been released.
• Before removing the pressure cap, check the temperature of the cooling system with an infrared temperature gun if you have one available.
• When removing a radiator cap, use appropriate gloves, clothes, full face shield, etc.
• Before commencing a repair or service task on the cooling system and allow approximately 30 minutes for the system to cool sufficiently before opening the pressurised system.
• When removing a radiator cap, use appropriate gloves, clothes, full face shield, etc.
• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Drain the at least 50% of the coolant in the system to avoid spills.
• Position the thermostat air bleed valve (if fitted) in the proper position.
• Make sure the thermostat is fully seated in the groove and stays there before fitting the housing. Failure to do so will damage the new thermostat and possibly break the housing as it is tightened up.
• Tighten the housing bolts to the correct torque.
• Make sure to use the manufacturer’s procedure to properly bleed all air from the cooling system.

Part 2: Step-by-step instruction

1. Remove the thermostat
   Unbolt the thermostat housing from the engine block. Be very careful not to damage the housing as it is generally made from aluminum or a similar fragile material. Remove the thermostat.
2. Inspect the mating surfaces
   Inspect the thermostat housing and remove any gasket material from the mating surface of the housing. Inspect the engine block and remove any gasket material from its mating surface.
3. Install the new thermostat
   Inspect the new thermostat to ensure that the identification number is the same as the one you have removed. Fit the new thermostat, ensuring the air bleed hole is in the correct position. Check the thermostat is fully seated in its groove. Fit the correct type of gasket for the vehicle you are working on. Carefully refit the thermostat housing to the engine block and bolt it into place.
4. Refill the cooling system
   Refill the system with coolant. Run the engine to circulate the coolant and remove any air trapped in the system. Check that the temperature indicator gauge shows the coolant temperature is in the normal operational range. Top up the radiator or reservoir with coolant if necessary.