Cooling issues

[Scmitt]

Update! I back filled the coolant system! The expansion tank was about half full. I removed the bottom hose (from rad to t/stat) and filled it with coolant until it came out of the sensor hole. Replaced sensor and filled as much as I could then refitted hose to t/stat. I removed 1 heater matrix pipe and added some coolant. Then ran engine. All seemed ok. Heater working in car. Temp gauge showed half way. Stayed steady for about 20 mins. Electric fan didn’t cut in (relatively cold day) and gauge stayed steady in the middle. Hopefully ok now!

 

[Zephyr]

You need a scanner. It will show coolant temp and circulation sensor temp.
when you first start the car both will be at -40. Then when the coolant temp reaches 108ish the circulation sensor will start showing numbers going up to 60 on a cold day.
that would be the time to check the voltage on the fan. If sensor temp goes over 90 and the coolant climbs up to 115, without the fan kicking in, turn off the engine and check what is wrong. Do not trust just the gauge on such an operation.