Make sure you have bled the system properly! To Bleed System, follow below taken from the WQ Work Shop Manual:
For 1.3/1.4 or 1.6L..
Filling and Bleeding
1. Remove the radiator bleed plug (if equipped).
2. Fill the coolant expansion tank until coolant
is expelled from the radiator bleed point or
stabilizes at the MAX mark (whichever occurs
first).
3. Install the radiator bleed plug (if equipped).
4. Fill the coolant expansion tank to the MAX
mark (if necessary).
5. Start and run the engine at 3000 revolutions
per minute (RPM) for two minutes.
6. Fill the coolant expansion tank completely.
7. Install the coolant expansion tank cap.
8. Start and run the engine at 3000 RPM for
another two minutes.
9.Switch Engine Off
For the 2.0L
Filling and Bleeding
1. Fill the coolant expansion tank to the MAX
mark.
2. NOTE: Do not allow the engine to reach
normal operating temperature.
Start the engine, run the engine briefly at
2500 revolutions per minute (RPM) for 10
seconds to prime the heater circuit.
3. Switch the engine off.
4. Fill the coolant expansion tank 15 mm over
the MAX mark.
5. Install the coolant expansion tank cap.
6. Start the engine, maintain the engine speed
at 2500 RPM for eight minutes or until the
engine reaches normal operating
temperature.
7. Maintain the engine speed at 2500 RPM for
three minutes after the engine has reached
normal operating temperature.
8. Increase the engine speed to 4000 RPM for
five seconds.
9. Decrease the engine speed to 2500 RPM for
three minutes.
10. Increase the engine speed to 4000 RPM for
five seconds.
11. Decrease the engine speed to 2500 RPM
for three minutes.
12. Switch the engine off.
13. Check the cooling system for leaks.
14. Allow the engine to cool.
15. Fill the coolant expansion tank to the MAX
mark.