Replace your coolant temperature sensor. My thermostat went bad and broke apart so I replaced it. Worked fine for a while but then it would not reach operating temp or the needle would move around on random occasions. Thought I got a faulty thermostat so I replaced it again and did the same thing. Decided to replace the coolant temperature sensor and now I haven't had any issues. The part was like $12 on ECS for an aftermarket one or like $60 for OEM. Aftermarket one looked identical to the faulty OEM one. Install was only 15 minutes. You just reach in under the SC pulley and you'll see it there. Unplug the connector, pull out retaining clip, and sensor comes out.