I have replaced radiator and cap. My jeep will build more pressure in the radiator and coolant will be leaking through and overheat. When checking coolant level it will be low. Removed thermostat still doing the same. At start up white smoke from the exhaust noticed and the fade away but smell of burnt coolant and starting up will be like it is misfire and the idle fine in less than 30 sec. What couls be wrong?