So i drove my monte today & when i turn the heat on it gets a bad Antifreeze smell that dont really go away, is this a bad heater core issue?

 

check the coolant level then start the car and watch the coolant elbows to make sure they haven't fractured or blown the o-rings, after that is ruled out i'd have to go with the heater core being the culprit

 

that is usually a tell tail sign of a bad heater core

 

Heater core going bad also can make your windshield fog up

 

It's usually a tell-tale sign of a bod core BUT it could also be a coolant leak under the hood moving the smell in through the fresh air intake.

Time to pressure test.

BTW - If it is, i'll sell you a heater core from my '04 with 62,000 mile on it, not used in winter since I got the car in '08. There is nothing wrong with it, I changed it because to change the evaporator core for my A/C I had to remove the HVAC module that holds both cores. I'd NEVER have an easier time doing the job (though doing the heater core would be much easier then the Evap core, no need to remove the HVAC module).