[Chromehero]

You might start with the Temp Sensor. It is called something different now, but function is the same. It is on the Head of the engine on the Driver's side (at least it is on mine).
It should be cheap to get another one, but it is difficult to replace due to it's location.

If you are looking for faster/easier things to check: see if you are leaking coolant. Check your hoses. If the level is low, that could cause it to fluctuate wildly.