The OEM thermostat never just opens and then stays open it will open/close constantly. That is why if you monitor the temps you will see a "cycle" from cool, warm, and back down to cool.

I owned D2's when they were brand new and I can guarantee you they were doing 210-215F right off the showroom floor. I never killed one or did I have any head gaskets replaced. 188-210F is the norm operating range in my book. I'm normally at 188-204F as a range. I wouldn't really worry unless I saw it climb above 210F. Then I would certainly investigate.

 

This what I recommend doing after an initial system bleed per the manual. If you do this each morning when stone cold until you can add no more it woks very well. Clean and cuts down on coolant waste. All you need is a small funnel. It's also a good idea to do this occasionally to ensure your system is not getting too much air into it.
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