Chevrolet Repair: 1994 gmc blazer overheating, water temp gauge, gmc blazer

Question
I have a 1994 gmc blazer v6.  Last year I had the water pump replaced and its been running cool ever since.  I let my wife borrow the car for work last week and when she returned home she mentioned the water temp gauge was pegged.  I looked it over and there where no appearant leaks on the system.  I removed the radiator cap while the engine was running and there was coolant flow.  The fan was moving belt driven.  I did feel the out going hose from the intake manifold where the thermostat is and the hose felt cold like there was no flow out going.  Its possible the thermostat may need to be replaced.  Any ideas on what the next step would be to determine what is causing this to run hot.  Car has been parked ever since this started. hope to get this going again.  

Answer
Hello Danny,
The flow could have been what was going through the heater hoses, and the thermostat could be closed, but I am surprised there wasn't a lot of pressure in the system.

And it may not be running hot...it could be the wire to the coolant temperature sender.
With a gauge, it has a sender in addition to the coolant sensor for the computer.
The sender is beside the #1 spark plug I believe.
Pull the wire off, and see what the gauge says. Then ground the wire and see what it says.
One way should max hot, and the other way max cold if the gauge and fuse are good. You could just need a sender if the gauge does as described.

As for the thermostat...one way to see if it opens is to unhook the upper radiator hose, and see if coolant flows out.
They are only about $6.00, so replacing it would be a cheap easy option.

Van