Honda Repair: heating & cooling, coolant system, gauge cluster

Question
"I have a 1989 accord lxi fuel injected, auto, 160k miles. It takes a long time to warm up. when i hit the road the temp gauge drops to cold and climbs back up to normal when i park but I have heat inside even when the gauge reads cold. Fluid seems to be circulating when idleling. the thermostat has been changed. What could be happening here?

       thanks, jim

Answer
Jim, flush the coolant and completely replace all the coolant. The themostat has been replaced - good. Bleed the coolant system properly there is a port to do this. I know there is a temperature sending unit located near the thermostat and this could be what is causing the inaccurate reading on the gauge cluster. Or the gauge cluster itself is failing, but, doubtful.