Hi, there is several items that can cause this concern. I have a few questions that will help me help you.
Does the heat and a/c work? wil the cooling fans stay on when climate control is off? Is the coolant at the proper level in the reservoir? After the engine is warm and the cooling fans turn on, is the radiator hot or cool (don't burn yourself), does the air from the fan feel hot?
Hi, it is possible that the new thermostat is opening too late and opening just above the the fan turn on temp. causing the fan to run all the time after the vehicle is warmed up. The engine computer will turn the high fan on around 220' F. If the thermostat is opening at 225' F then the engine will never run cool enough for the fan to turn off. this would still keep the guage in the normal range. What brand thermostat was used? what part number was it? Was the thermostat installed correctly? See if the radiator gets hot after the engine gets a little warmer (engine will heat up quicker if the heat is off). Is there anything blocking the flow of air across the radiator? Where is the temp guage when the fans turn on?
The easy way to diagnose this would be to hook up a scan tool and monitor the coolant temp and fan commands to see if the fans are working per the engine control computer. There may be a concern with the temp sensor or a wire harness issue.
Does the fan start at a low speed at first before the high fan turns on?
Do you have a scan tool? Do you have a digital volt meter?
check to see if you think the t-stat is not opening soon enough. see if the engine will over heat with the heat off.
Let me know what you find at I will get back with you on Monday.
Great, I thought this was going to be a painful road to a solution. All you have to do is accept the answer.