without knowing what yesr make and model of car it is hard to determine the problem,but I will be willing to bet that the cooling fans aren/t working .
Has the air been bled from your cooling system?
Does the fans work when temp gauge reaches 3/4?
Was the water pump changed with the radiator? The pump is the key to the whole system. And ask your mechanic if the system has been pressure checked and whether the system was flushed when the new radiator was put in. Corrosion inside the engine will inhibit cooling just like a corroded radiator. Also, as noted above, most newer model cars have an electrical switch which turns on the radiator fan when the engine gets hot (maybe this is your AC sensor switch you note?). In any case check that the radiator fan comes on when you idle with the AC on---do this now in your driveway.
Report back to us on your findings if you need more help.
If the head gasket is leaking hot gas into the coolant you will see a marked change in the color of the new coolant that was added when the radiator was changed. The coolant was probably red---maybe green. Check the color by opening the expansion tank. If the color has not changed significantly then the head gasket is not the problem.
I'm sorry it's a 2004 Hyundai sonata and I also got the head gasket replaced when the radiator was done because both had leaks.
It would be easier to help you if you had listed the year, make and model of your car.
#1. Have an inexpensive *cooling system pressure test done to see of there are any external or internal cooling system leaks.
#2. When was the last time that your cooling system was drained, flushed and *CLEANED with one part powered acid cooling system cleaner to get the corrosion, rust and slime out of the heater core, radiator and water jackets?
#3. When you run the air conditioner it will make the engine run hotter.
#5. To cool an overheating cooling system turn the heater on with the temperature set at maximum.
According to my bf, the head gasket. Which is big bucks. Sorry to be the bearer of bad news. I don't think this will help but mine is mickey moused and you have to keep the fan on low, so try different speeds and settings to see if that helps, otherwise I'm afraid you will have to live without AC or decide if the head gasket is worth fixing on your car.
are your fans working ?
I've already replaced the radiator, got new hoses (2), changed the AC sensor and put in a new thermostat. My mechanic doesn't know what else it could be. I'm so frustrated and want this to be over. What could it be??? Any idea?
