I have exactly the same thing right now !!
ORdered a new thermostat friday, will change it today or tomorrow.
In my case it's after a water pump change, so I hope it's just air pockets.
Will try to empty the coolant, and refill. Trying to find a hagh enough spot to be able to get the air pockets out.
But I am afraid it can be the mixture of 2 differant coolants, which I know is bad, but I didn't know what type they added in US so I had to just try. Will remove all, run with water once only.
If that works I will refill with new coolant. All from one supplyer.
