Overheating on 2000 Hyundai Elantra

When I am parked for a few minutes, the anti freeze starts to boil. it shoots out of the antifreeze overflow spout. It does not happen, when I am driving. Could this be the thermostat, or the fans?

Asked by for the 2000 Hyundai Elantra
it concerns me that you may have a real problem. get a leak down test done at a shop to see if compression is leaking into the cylinders from a head gasket. if it is not, a bad cap may be the culprit but not to the severity of what you are describing.
get it done asap so you do not damage anything internal.

1 more answer
I had the same problem. Found out the bypass hose was leaking and running low on coolant causing the overheating. Bypass hose is on the driver side of engine just below valve cover at front corner of block. Only overheated every now and then as coolant level dropped too low. Very slow leak.