1992 Honda Accord Temperature Gauge

Engine Cooling problem
1992 Honda Accord 159774 miles

My temperature gauge in my recently purchased Honda Accord 1992 fluctuates a lot according to speed. It will rise rather high, not into the red but up there, then it will drop back down. The rhyme and reason behind it seems to be involved with whether it is in a higher gear while driving in the city, or a lower gear while driving in the city. It will go up on the highway, but not as high as when stopped and idling. Coolant is full with mixture of water and coolant (mostly coolant) and there doesn't appear to be any leaks. Suggestions?