For those in Australia - SuperCheapAuto have in their Easter Sale Catalogue available from 29/3/17 - 14/4/17 a Black Ridge brand Infrared Thermometer able to measure from -50C to 380C The sale price is $34.95 (40% discount) - a saving of $25.02. This enables the safe and accurate testing of your Coolant Temperature Sensor at an affordable price.  I have no commercial affiliation with SuperCheapAuto.

Thanks mate.  What do you mean - do you take a temp reading at the tower that houses the temp sensor?

That looks like a good buy for an infrared laser thermometer. I bought a cheapie off ebay a while ago that seems to work ok but the build quality is pretty poor. I've used it to measure various engine parts as well as my big toe.
The lasers are powerful so be careful how you use it as they can damage your eyes.
Getting a reliably accurate reading off reflective metal surfaces is difficult so you need to find a suitable spot to take the reading. If your engine is painted black all the better.

Response to Nod's post: You can more easily and thoroughly test a Coolant Temperature Sensor (CTS) by removing it, suspend it with the base rod part of the sensor (brass usually) immersed in a saucepan of water, heating the water on a stove and taking temperature readings and at the same time taking ohm readings with your multimeter. This enables you to get a good idea of how your CTS is functioning at various temperatures and then make a decision to refit it or replace it. A scale of temperature to ohm readings is posted elsewhere in this and on other forums.

Where exactly would you aim the Infrared Thermometer to get an accurate indication of the coolant temp?

Cheap coolant sensor $10.92 US shipped  https://www.aliexpress.com/item/High-Quality-Engine-Coolant-Temperature-Temp-Sensor-For-BMW-Motorcycles-K-100-K-75-K75-K100/32680512124.html? Doesn't work.
Regards Martin.

michaelvass wrote:Where exactly would you aim the Infrared Thermometer to get an accurate indication of the coolant temp?

Metal surfaces won't give you an accurate reading especially if they are really shiney. Probably best to aim it at the bottom of the left side of the radiator itself. Its black plastic. This is where the coolant enters the radiator from the crankcase and it will be at its hottest.

To accurately check the temp sensor you need to pull it out and place it in a controlled environment with hot water and a thermometer, then check the Ωvalue against the chart in the trouble shooting section off the Portal Tab.

Alternatively, just assume that when the engine has been sitting overnight, the coolant is around ambient temperature. After running for around 10 min and the fan kicks in it's at operating temp. Do a rough check on the temp graph at those points. Personally, I think this is all you need