Is the temperature on the guage coming up to around 85 degrees C? If so, then your thermostat is not your problem. If the temp is not coming up, then the thermostat is near the front, drivers side of the engine.
To check the control valve, feel of the hose going to the valve and then the hose going away from it. If the hose going away is colder, then the problem could be the valve or the controls that actuate the valve.
Best of luck,