Hello & Welcome,
This type of symptom normally points to some air trapped in the cooling system.
Have you had any work done on the vehicle recently?
Have you tried to use your heater recently and noticed and temperature changes?
You didn't mention which engine you have, but I would check the coolant level at the radiator, when the engine is cool. I would also check any overflow bottle that you have and make sure that is has the appropriate amount of coolant in there too (between the Full Cold & Full Hot levels).
Please let me know what you find, or if you have more questions.
Thanks, XXXX X.
Master Troubleshooter
Working with Electronics & Cars for 25+ Years