1995 Geo Metro 1995 Geo Metro Leaking Coolant

My 1995 Geo Metro temperature gauge stopped working a few weeks ago (it constantly shows no temp). I drove it to work the other day and when I came out there was coolant under the car and the coolant tank was empty (like it boiled over). I refilled the coolant and drove the car home. When I parked it I could see coolant dripping under the passenger side of the car, however after the car cooled down the dripping stopped.

I refilled the resevoir again and let the car sit for 2 days without starting it and no coolant has leaked. Is the coolant loss related to the temperature gauge not working? Where should I begin looking for the problem? Thanks.