Golf Mk1 overheating

[buttle]

Can someone please give me a checklist of things to look out for an overheating problem.
I recently replaced the front manifold temp sensor and the actual plastic manifold that is fits into (there was a small pinhole leak in the side)
The water level is correct but after driving for about 15 or 20 mins... the Temp dial goes to max and the oil and temp warning lights come on.

Could the wax motor thermostat be dead?
Are there any other sensors that need checking?
Do I need to flush the radiator?

It used to run perfectly well for sooo long!!! and now this out of the blue
TIA

[Mk12009]

The temp sensor does exactly what it says which is sensing a temperature change and the fact that it gradually goes to max on the cluster means it is sensing and i doubt the issue is there.

1. First thing to check does the radiator fan kick in - it should within 10 minutes while car is idling - probably the sensor area, fan or fuse
2. If the radiator fan kicks in then
2.1
I would suspect that the thermostat is stuck closed and not letting cooled coolant to the engine
2.2 clogging somewhere in the coolant system

Check out this video for further details

https://youtu.be/iLaJAbmAuPg

[VAG Fan]

Peter, did you bleed the air from the system?

[Gavan]

Please check that the top 8mm pipe that goes to the water bottle is open on the radiator, sounds like air is trapped in the radiator

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