Sounds to me like the coolant is just low. Check it again even if you are sure.

Check the fan clutch by spinning it when car is stone cold. If it turns more than 1/3 turn by spinning it, it is dead.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k