Hyundai Repair: overheating, coolant temperature sensor, wiring relays

Question
2001 hyundai elantra, 2.0L, stick.
Replaced radiator due to top tank spliting after
engine over heating. Engine still over heating!
Help.


Answer
You'll need to investigate.  There are many possible causes of overheating.  If the coolant continues to leak out, you should repair the leak first.

Fill the radiator and let the car run with the radiator cap off.  Make sure the a/c is turned off.  As the car warms up, the thermostat should open and allow coolant flow.  As it warms further, the radiator fan should operate to keep the coolant at the desired temperature.

If the coolant never flows, there's a huge probability that the thermostat is stuck shut.  Replace it and recheck.

If the fan operates but doesn't blow hot air off the radiator, you don't have coolant flow.  See thermostat above.

If the fans never operate and the engine starts to overheat, then you'll need to diagnose the fans.  Turn your a/c on.  Both fans should operate.  If they do, you know that the fans, wiring, relays, and fuses are okay.  In this case, the ECM (Engine Control Module) is probably misreading the coolant temperature and not turning on the fans.  Check the coolant temperature sensor.  If one or more fans don't operate when the a/c is on, you'll need to electrically diagnose the circuit for the applicable fan(s).  

If you have coolant flow, and the fan blows hot air off the radiator, and you've gotten the air out of the system, you probably have an issue with your head gasket.  

Most importantly, don't try to drive the car while it's overheating.  I've replaced many cylinder heads because customers drove their car until the head warped.  Not cheap.