My 91 crx seems to overheat now whenever i have been driving awhile then find myself in traffic in town. it goes up, i turn on heater, then it goes down. Causes?

 

Fan not working, low on coolant, air pocket in the system theres a lot of causes for overheating

 

Do you have a thermostat installed (no thermostat = insufficient heat transfer inside engine)?
Does your fan come on (pull over and check next time you overheat)?
Do you need to refill with water/coolant often (suggests possible leak of faulty water pump)?