Could be a thermoststat failure. The engine gets hot, the radiator stays cool. To check for a bad thermostat, let the engine run with the hood open. One hose (to the radiator) will get warm, the other will stay cool until the thermoststat opens. When it does open, both hoses to the radiator are warm, along with the entire radiator. The air being moved by the fan should be heated by the warm radiator core.
If the thermostst does not open. the radiator will only be warm near one hose, and the cooling air flow will not be much warmer than the ambient temp.
It is also a possibility that the temperature sender is bad. Or, the wire is grounding somewhere...
