My car keeps over heating time to time i took it to the shoo and they cant even figure out why my fan do work can u help me also when it over heats i have my coolant leaking out from underneath my car

What is your question?

My coolant makes like a sizzling sound. And like boiling up and than has smoke and when it overheats everything is hot so I lose alot. Of coolant and sometimes the coolant goes down and comes right back up after it's done cooling off but now and now and than my car still keeps overheating I am not sure what's going on I'm hoping someone can help me find some answers so I can get it fixed at first we thought it was the fan because we let it sit with the AC running and then the car shop have me test drive my car for a while where I was on the highway doing 60 back and forth when I came back to check it he heard the fan was on. And still some reason not over heating and making smoke some reason today compare from the Thursday when it was overheating and smoking and everything else so now he thinks it might be the thermostat I've been driving it for almost 2 hours now and it's still not smoking for some reason today