I have a 1995 1/2 Honda Passport which recently began overheating after idleing for a prolonged period. The engine will warm up as usual and stay at a constant temperature for 10-15 minutes while idleing, at which point the temperature begins to rise. If the engine is idled up around 1500 rpm, the temperature goes down to normal. I've tightened the drivebelt for the waterpump, but that's all so far. Any thoughts?

 

Maybe new water pump, check coolant, new radiator, change coolant, and new thermostat but I say definitely check the thermostat.