Hi Peter,
My Aero Plus 8 does the same. Last winter the engine ran at 100 degrees gradually dropping away as the weather warmed. All summer the engine has been running at 90 deg but as soon as the temperature dropped again, it climbed back up to 100 deg. I kept a close eye on the engine temp while I was trying out Cain's prototype bump plate for him.
Tested over a good few thousand miles, the plate makes no difference to the engine temperature as far as we could tell.
