I also faced the same problem with my Xli few month back.
I approached the mechanic. He checked up the radiator and said to me to remove Thermosat valve.
I did not followed mechanic advice.
After few day I myself open the fan and radiator. I was surprised to see that radiator were leaking from the area behind the fan which was invisbile. (Very minimal discharge just wetting the outer surface of the radiator).
So my suggestion is to put back the Thermosat valve and do a complete checkup of radiator after removing it.
Thermosat valve removal is not solution to problem. It is used to get faster heater air in cold weather.