I suspect I have air in the coolant. Very intermittent coolant warning light when the engine is up to temperature yet the reservoir is up to max when cold. Don't believe it could be the thermostat as the cabin heating works fine, and can't see a failing water pump only giving an intermittent light, with no other signs of problems.
Figure trying to bleed it will be the simplest starting point anyhow, I had one hose out when I did the VANOS but that was months ago, curious how it's only started this recently.
Figure if it's not air, it might be a sensor going faulty?