My 1999 Honda Accord EX - The temperature hand will move up then fall down as I'm riding. This happens when I orgininally start it in the morning and will do it until it's been about 7 miles down the road. I'm not sure if something is wrong. It's never done this before.
You may need to replace your thermostat, this can form deposits over time and cause it to not open and close properly. This is a fairly cheap replacement cost, if your issue persists you have a lead towards a possible temperature sending unit failure.
〉 Answered on Mar 15th, 2013 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions