Pt cruiser temp gauge fluctuates from below normal to above normal

Replace thermostat. It is stick open causing the engine to run too cold.

Car overheats Chrysler Vehicles Ricks Free Auto Repair Advice

does the temp gauge work? if not check the coolant temp sensor and circuit. its on the passenger side below the radiator cap and pipe.

Is there 2 Sensor's on your Car?

One for the Gauge and one for the Computer?

could be the wiring, faulty temp gauge in the dash. or bad temp reader inside the engine. located where the top hose enters the engine.

try topping it up when cold ,sounds like a air lock

2 tests
1-- compression test for gasket and cracks
2--- coolant system pressure test to check for split tanks , welsh plugs , leaking through corrosion holes behind pump impeller

I just had the same problem happening with my 2006 PT Touring. Took it to the dealership. The issue was the electric parts of the ignition switch. They replaced it and all is well in the world again.

I’m happy to assist further over the phone at https://www.6ya.com/expert/ryan_d3121b5304fa33c4

sounds like it is a temp sensor. should be 2 one for the fans and one for the gauge inside the car. it should be the one by the thermostat housing for the gauge.

check coolant level ,must be low ,chck for coolant loss