Coolant smell in cab

i replaced the heater core about 5 months ago. the radiator is about 3 years old. i get a hot coolant smell in the cab, coming thru the vents. sometimes a haze or smoke will come thru the vents also. 89 Ford Ranger. Could it be that the heater core has failed again or could it be something else??

Unless the connection(s) at the heater core/hoses is leaking and spraying into the cabin the heater core is leaking.