Hyundai Repair: Hundai sonata overheating, hundai sonata, coolant level

Question
I have a 2002 sonata 80,000 miles.  I had the timing belt replaced a couple of months ago.  It didn't break but the ridges on the inside were coming off.  this broke the sensor by the belt.  Now about a month later the car began to overheat.  I saw fluid by the sensor on the right side of the motor between the cover and the fuse box cover.  It was replaced but this didn't stop the overheating.  they replaced the thermostat today and it overheated again.  it doesn't go into the red but I have to drive with the heater on to keep the temp down.

Answer
The first thing that concerns me is that it sounds like you may have a coolant leak and haven't corrected it.  The engine cover has nothing to do with the cooling system, so I'm troubled by the coolant that you found, although I'm not exactly certain where you found it.  If the coolant was on something that doesn't contain coolant, then the coolant was originating elsewhere and spraying onto the area where you saw it.  First, you should check your coolant level and, if low, check for and repair any leaks.

My next concern is that an incorrect temperature thermostat may have been put in your engine.  Since you report that the gauge doesn't go into the red but runs hotter than normal, this is a distinct possibility.

If the above items are okay, you should do an audit of your cooling system's performance.  With the radiator cap removed and the a/c off, start the engine.  As the engine reaches operating temperature, the coolant should begin to flow prior to the fan coming on or the coolant boiling out.  If it doesn't you'll need to check for blockages in the cooling system.  A stuck thermostat is the most frequent issue.  If yours has the correct temperature rating, I'd suspect that's not the issue since it's new.  The next typical culprit in a lack of coolant flow situation is a clogged radiator.

Once the coolant begins to flow, the radiator fan should begin to cycle on and off as the engine temperature increases.  If the coolant begins to boil out prior to the fan coming on, you'll need to diagnose the radiator fan control circuit.