I've had this van for four years and all that time the dash temp gauge has remained steady well below 90 (or halfway).

Two things happened during a journey in the very hot weather recently.
1) The Glow Plug Light started flashing and doesn't stop until the ignition is turned off.
2)The dash temp gauge flicked up over 90 and stays there now as a new "normal".

Could the two things be connected and if so where do I look to solve the "problem"?