Temp gauge fluctuating

[Klaatu4u]

I’ve got a 2009 People 250.  Having a temp gauge issue.  When I ride...after 5 min, the temp is at about 50%, which is normal.  A few minutes later, it will climb all the way to max H.  And, after about 15 seconds, it will fall back down to 50%.  This just keeps repeating itself every few minutes for the duration of the ride.
I have about 10,000 miles on it.  Never had an issue.  My local Kymco dealer / maintenance shop closed down a while ago, and I am not sure where to take it for repairs here in South Jersey.

Any thoughts?

[Tromper]

I had a similar problem with one of my SYM's.
The factory coolant had never been changed out.
I did a flush and fill then bled the system & topped it off one more time.
The flush did got a lot of junk out, but still had some of that. the final top and bleed seemed to get the last of that.

[stuo]

What a coincadink! I had an old People 250 that had the same problem. It was a (very) used bike and when I got it home the coolant looked like it had never been changed: it was a brown sludge and after flushing/refilling...no more problem.