You may not have a water valve, but if you do, it's inline with one of the heater hoses. Years ago they had a cable running to them from the controls on the dash. Today they're run by a vacuum motor and will have a small vacuum hose going to it.
If the heater hoses are just as hot as the radiator hose, coolant is circulating through the heater core, and the temperature door in the heater box is suspect. Look for a cable from the temperature lever that is slipping on the door's lever, or a vacuum hose that is disconnected or leaking.
The temperature door can be rusted in the "cold" position too. That's when a cable-operated lever seems to work, but actually where that cable connects to the door's lever is supposed to slide somewhat freely. That is the self-adjusting feature, but when the door is stuck, the cable slides back and forth in the adjustment without moving the door. This problem usually shows up in winter after the door has been in the "cold" position all summer and had a chance for the metal hinge pin to rust.
If the heater hoses are not as hot as the radiator hose, the heater core could be plugged. To clear it, remove one of the heater hoses from the engine, and the radiator cap, then run water into the hose from a garden hose. If the water doesn't flow freely after a few seconds, it may be necessary to remove the other hose and run the water the other way.
Tuesday, January 27th, 2015 AT 6:10 PM