Temp gauge says car is running hot

[schaery]

Several weeks ago, temp gauge on car indicated car was running hot. Mechanic found a crack in the radiator and replaced the radiator. Now temp gauge is going up again. Check radiator and coolant reservoir but both are full. What else can I check?

Also, gas gauge fluctuates up and down constantly. Is there an easy and inexpensive fix for this?

[maxhopper]

Check for air in the cooling system. Check for proper operation of coolant temp sensor and thermostat.

Not sure about the gas gauge issue.

[MTZI30]

Can you be more specific? How hot exactly? Like way near the top of the gauge? How much does the gas gauge move up and down? Like its constantly moving or it just seems off? I'd say that the overheaing could be a sticking radiator or maybe the fans arent coming on. The gas gauge could be a gauge problem itself or maybe the meter in the tank.