So i took my sons 2000 ranger (V6) to the store today and noticed the engine was still cold even though i drove it for several miles, and the defrost was blowing cold air. on my way home the temperature gauge shot up to the red line and the heater was still blowing cold air. I have read various websites on things to check but still no hot air even when the engine is up to temperature.
1. upper rad hose hot once t-stat opens. T-Stat good correct?
2. valve to heater core opens when i turn selector switch inside the cab to the off position, and seems to close when i turn it to any other position but off.

 

I would check the coolant level with the engine cooled down. If there's enough coolant, the sweep to the red zone is an indicator that the engine was getting too hot. A sticky thermostat can cause that, or low coolant level that prevents the hot coolant from touching the sender that operates the gauge, until it expands enough.
Both heater hoses should be too hot to keep contact with when the engine is at normal operating temperature, and the valve is in the open position. If one is cold or warm, flow is likely restricted due to coolant level, a plugged up heater core, or a failing pump. The last should lead to overheating in normal operation.
The upper radiator hose should stay cool, and then get warm/hot when the thermostat opens. It will seep very little coolant past the thermostat until it opens. There may be bleeds built into the stat, or check valves to allow filling the system with coolant without an air-lock.
tom

 

Do both heater hoses get hot after the engine warms up? If not I would try back flushing the heater core and maybe replace the heater control valve. Is the cooling system due for a flushing?

 

I had very similar symptoms one time when the t-stat in my 4.0L failed. It seemed like it was sticking open, then sticking shut. I changed out the t-stat (Motorcraft brand) and problem fixed.

Note: If you do change out the t-stat, you need follow-up and make sure that air is bled out of the cooling system.