Temperature reading on engine

[dgrinnan]

Where on the engine would be a good location to take a temperature reading? I have an after market temp guage mounted under my dash.  It seems to show a  normal operating temperature of 190.  I do have a 180 degree thermostat.  I want to check the accuracy or deviation of the temperature gauge. 

[TodFitch]

If you measure the temperature near the sending unit (bulb) on the left rear of the block you should be reading close to the temperature the bulb is sensing.