coolant temperature goes up and down at slower speeds?

Here is a guide to help you see what's going on with additional related guides:

https://www.2carpros.com/articles/engine-overheating-or-running-hot

1. Low coolant level. You need to pressure test the system to verify no leaks.

https://www.2carpros.com/articles/radiator-pressure-test

2. Thermostat. Common problem s it sticks.

https://www.2carpros.com/articles/replace-thermostat

3. Clogged radiator. I would flush the system.

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Roy