Hyundai Repair: cooling fans 2001 sonata, combustion gases, coolant level

Question
engine was hot enough to boil over!
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Followup To

Question -
cooling fans will not start and temperature guage will not rise although the engine is warm.

Answer -
First, check your coolant level.  It's possible your coolant is low.  Second, if you temperature gauge does not rise and the fans do not come on, how did you reach the conclusion that the engine was warm?  I'm curious about the likelihood of the possiblity that the engine wasn't hot enough for the gauge to rise or the fans to start.

Answer
Gotcha!  Primarily, I'd suspect air in the cooling system, preventing the coolant temperature sensors from properly reading the coolant temperature.  If your coolant is low, check for leaks.  

Also, you should suspect that the thermostat may not be opening, and has caused the coolant to boil out through the overflow.  

It's also possible you have a head gasket or similar engine problem leaking combustion gases into the coolant, but that's a rare problem on this engine.