Take out and put in a pan of boiling water!!
Check the thermostat, it may be stuck in place.
check coolant level check thermostat may be stuck closed
Check the engine thermostat. Its probably stuck open.
Check for a stuck open thermostat, check for an always on radiator fan, control valve stuck partially open or a clogged heater core.
Check your thermostat. Probably stuck open.
Check your thermostat, it is either stuck open or not in the engine.
Check the serpentine belt or Thermostat stuck.
When the car is hot, squeeze the upper radiator hose. If it feels soft, then the thermostat is not opening and therefore bad. If you squeeze the hose and its hard to squeeze, then it is pressurized and the thermostat is open. That is one way to check if the thermostat is stuck closed. If the thermostat is stuck open, then in cold conditions the car will take a long time to produce hot air from the heater.
I would suspect the thermostat is stuck open. Replace the thermostat.
Check your heater core and thermostat. The thermostat may be stuck open. Does the S10 run hot or cold?
Yes. Check that first. If you are not getting heat then it could also be a stuck thermostat.
Check the coolant level. Or, thermostat could be stuck in open position.