Temparature guage runs hot then comes down. coolant and oil are fine on 2000 Saab 9-3

I was driving and noticed that the temp was moving towards hot. Checked coolant and that was fine. Noticed oil was very low, changed oil and started to drive again. When I started driving the temp ran towards hot and emergency light came on again. Let the car cool down and drove on freeway and streets, gauge started to move up near hot but not crossing the line over to hot.

Asked by for the 2000 Saab 9-3
Replace the thermostat!!!