2005 Honda Pilot. Temp guage goes up but then comes back down to half when the a/c or defrost is on. If sitting in traffic is still goes up until moving again.

There are several possible problems causing the temp increase.

1. Low coolant level
2. Leak in radiator hose
3. Leak in radiator
4. Bad waterpump

With low coolant levels by any 1 or a combination of 1-4, the vehicle will run hot at low speeds and at idle. Running the AC or heater pushes the remaining coolant through the system faster, aiding in cooling the engine but all indications are you've definitely have a cooling system issue that should be looked at immediately before doing damage. If the coolant level is good (when car is cold, open radiator cap and check for coolant level), the issue most likely lies in the waterpump.