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Replacing the Thermostat

How to replace the thermostat in a car

MY ENGINE HAS OVERHEATED, WHAT DO I DO?

There are two signs that your engine has overheated.

One:
The temperature gauge shows hot.
Two:
The coolant warning indicator light comes on while you are driving.

If you see either of these signs, stop driving as soon as possible and allow the engine to cool down for at least 15 minutes before checking it. If you remove the radiator cap before the engine has cooled down, the pressure released when you open the radiator cap will severely burn you.

Use a cloth or rag to remove the radiator cap, this will reduce the risk of burning yourself should the radiator not have cooled down completely. Most radiator caps come off in two stages: a quarter turn will allow most of the pressure to be released without letting out a blast of steam, and the second quarter turn will completely release the cap.

When the engine has cooled down fully, check the level of coolant. You can do this either in the radiator by slowly removing the radiator cap, some cars have a plastic expansion tank where the coolant level can be seen easily.

Do not top up an overheated engine with cold water, as this could result in engine damage. Wait until the engine has cooled enough to touch by hand.

STEP 1:
Drain and flush the cooling system

STEP 2:
Remove the thermostat housing, old gasket and thermostat

STEP 3:
Clean the gasket mounting surfaces

STEP 4:
Install the new thermostat (spring end towards the engine) and the new gasket

STEP 5:
Replace the thermostat housing and tighten

STEP 6:
Refill the cooling system with the correct ratio anti-freeze summer coolant, whilst the engine is running

STEP 7:
Once operating temperature is reached, check the coolant level

STEP 8:
Check the new housing, hose, clamps and radiator cap for leaks

TESTING THE THERMOSTAT

The thermostat can be tested by putting it in a cup of boiling water for 3 to 5 minutes. If the thermostat does not open, then it could possibly have been damaged by previous overheating caused by:

  1. The coolant not being of the correct ratio for the engine
  2. A faulty pressure cap
  3. A dirty radiator (blocked cores)
  4. A defective water pump
  5. Loose belts that drive the water pump
  6. A defective fan clutch/ electric fan motor
  7. A defective thermoswitch

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