Hyundai Repair: Car Overheating, coolant leaks, radiator hoses

Question
I have a Hyundai 2000 GLS. I recently had an oil change, and immediately the car overheated. Since that time the thermostat and the fan belt was replaced, and it still runs hot while in stop and go traffic or long periods of idling. The smell of antifreeze is evident.  

Answer
First, you'll want to check the coolant level.  If the coolant is low, check for and repair any coolant leaks and recheck for overheating.

Since the car overheats only in stop-and-go traffic or when idling, you should expect a radiator fan issue.  Turn on your a/c.  At least one of the fans should run.  Check your radiator and condensor fan fuses in the underhood fuse box.  Neither should be blown.

If at least one fan runs and the fuses, you should check whether the fan operates based on coolant temperature.  Since this involves starting cool and taking the car to operating temperature, it's a good opportunity to do a good audit of overall cooling system operation.  

Remove the radiator cap and start the car (a/c off).  As the car reaches operating temperature, the coolant should begin to flow.  If you cannot tell by looking into the filler neck of the radiator whether the coolant is flowing, you can also test by checking the radiator hose temperatures and air temperature blown off the radiator.  If one is hot and the other is cold, the coolant is not flowing.  If the radiator fan blows cool air off the radiator, the coolant is not flowing.  If both radiator hoses are hot, the coolant is flowing.  The coolant should begin to flow prior to the cooling fan coming on and prior to the coolant beginning to boil out of the radiator.  If not, you've got a blockage somewhere in the system (or the water pump impeller came off (very, very rare)).  Since you've already replaced the thermostat, my next suspicion would be that the radiator is clogged, if you indeed do not have coolant flow.

Once the coolant begins to flow, the radiator fan (driver's side) should eventually begin to cycle on and off.  This is because the coolant will eventually get too hot unless air is blown across the radiator.  If you have coolant flow, but the coolant begins to boil out prior to the fan coming on, you have a problem with the fan control circuit.