[DrMaserati]

Remove the temp probe/sender from the engine. With the gauge wire attached, suspend the probe in a pan of hot/boiling water along with an accurate thermometer. The thermometer and the gauge should read close to the same. Keep in mind that factory gauges are not known for great accuracy, so there will probably be some small difference.

While we are on the subject of testing, here's another tip. In the shop where I used to work, we NEVER installed a new thermostat without testing it first. Suspend the thermostat in a container of water along with a thermometer. Heat the water and you will be able to watch the thermostat open as the water temp rises and while you monitor the temp. Make sure the thermostat is suspended in the water and not in contact with the container.

JP