THERMOSTAT

If the car warms up normally and it does not overheat the thermostat is OK. You could use a non contact thermometer on the thermostat housing to check temperature.

Using the "non contact thermometer" as FOR suggested is the best way. Start with a cold car and then monitor the temp of the housing. It should continually, but slowly, rise until the thermostat opens at which time the housing temp should jump up as the hot water that had been held in the engine block is released into the radiator through the thermostat housing.