my friend picked up a 2000 civic 1.6 automatic
coolant was low when she got the car so i filled it up using the funnel that attaches to the radiator let it purge the air about 3 months ago.
then the other day shes either on her way to or back from going to the beach. it starts over heating the needle goes from about 3/4 of the way then in the red she kept driving and it ended up going back down but the whole time it was in the red the car never lost any power or felt she said. and no check engine light and no code. so i added more coolant with the funnel and she said its only done it once on her way to work which is about a 30 min trip no the freeway and some up hill. im thinking its a possible thermostat or temp sensor or temp sender. but im not exactly sure. i was thinking about doing a timing belt kit and thermostat, temp sensor and sender but money is tight.

 

Pressure test the cooling system in an attempt to determine the reason for the coolant loss. AutoZone or other parts stores may offer a free rental for the required tool.