Drinks or loosing - the latter is much cheaper.
Temperature woes - first to check would be the wiring of the temp. sensors around the thermostat. Readings when it opens - if at all, if not then replacement. If the thermostat is not opening then the coolant gets over-pressurised and thrown away by the valve in the overflow tank cap - check if there are marks/wet.
Check for leaks around/under the water pump.
First off be careful , modern engines only have the minimum coolant quantity these days , no excess reserve. This is to keep the C02 levels down , but creates another problem in modern engines which can overheat very quickly & damage the head gasket as a consequence.
So if it’s overheating badly your not doing the engine any favours , is there coolant coming out the expansion overflow pipe ? If so it could be the cap needs replacing with a new one.
You could have a faulty water pump , if you’d lost about half your coolant the air coming out of the vents would be cold.