My charger has been having some coolant issues when i idlr it for to long the coolant begins to bubble in the over flow tank and there is no heat sometimes what could be the problem? When it has these symtoms the heat gauge never goes over half ways. Could it be the fan or the termostat or in need of a rad flush??

I would check the thermostat it might not be letting the water pass
Or you might have air in the system