What is going on with my car?

Could be a bad thermostat or air in the cooling system. You should have warranty coverage!

When you turn the heater on,. The little fan that blows your heat inside the car is also helping to cool your engine coolant. But after that coolant runs thru the engine the gauge should keep pretty steady. If it keeps varying in temp. Then your probably low on coolant and may have a leak. There are other things that could affect it, like warm water pump or bad thermostat. Those engines were made to run at over 200 degrees Fahrenheit up nder pressure, if you have a leak you will also have little pressure and you can't continually run any motor at 200 degrees unless it has proper pressure in the cooling system. They did have problems with the filler bottle if it is a seperate plastic bottle up on the passenger side strut tower,. The cracked and leaked often and that causes it to run to hot