Cooling Fan comes on 5-6 mins after starting engine - stays on. Periodically temperature gauge goes into red - stays there for a while then back into middle. (this possibly happening on certain bends / slopes?) More recently staying in red for longer - Temp warning light & engine warning light coming on.
Coolant levels OK - no leaks.
Have changed thermostat - no effect.
Changed engine temp sensor - problem may have got worse.
When you renewed your timing belt (due at 10 years old) did you renew the coolant (water) pump at the same time? If not I'd suspect the coolant pump.
If neither have been renewed yet do it now and give the cooling system a good back flush while you're at it. There could well be a heck of a 12 year build up of sludge in your radiator. If it is too bad then a new radiator could be on the cards too.
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