Losing coolant Options

[team_omega]

I dont know why im losing coolant...no leaks.....every time i drive far(about 200 or so mile) the car starts to overheat. I always have the refill the radiator. And the resivior takes all the coolant but only spits it back in the radiator when it over heats. But when car over heats the coolant in the resivior boils up and starts spitting it out too...there's a little hole on the right side underneath the cap of the resivior(on the tube)....it looks factory to me....so im thinking its my thermostat...what do you guys think???

[Supersprynt]

Thermostats not on the resovoir, but that could be a miscommunication.

Are you noticing any white smoke out your tail pipe?

Check your crankcase for milky-white substance and maybe change your oil too and take a look see if its contaminated. Compression test wouldnt hurt, and if all that checks out, could be ur thermostat gone bad. Did you have a leak and fix it with radiator fixer? Sometimes that clogs something it shouldnt and cause an interruption in flow.