After just buying this 1999 Ford Ranger 3.0 L and driving a long distance, the truck ran hot when stopped at an intersection. After inspecting I realized there is no thermostat. I added radiator flush and ran the motor for a while then tried to drain the radiator but nothing would come out of the stop cock. The top radiator hose is hot to the touch. How do I diagnose the problem?
If nothing will come out of the petcock, then you will need to drain it by removing the lower radiator hose. Chances are the radiator is plugged.
As far as not having a thermostat, that in and of itself can cause the engine to overheat. Without the thermostat, there is no restriction for coolant flow. Thus, the coolant has no time to cool when going through the radiator.
Drain the cooling system, flush it, make sure the radiator is clean and not plugged, and replace the thermostat. My GUESS is someone removed the thermostat thinking it would stop it from overheating, but the real cause is a plugged radiator.