Coolant Smell From Air Vents.

[blue2000s]

It very well could be the heater core. It could also be a radiator or the water pump or the air/water heat exchanger or the tank or a hose fitting. It's hard to tell because the smell can find it's way into the cabin from everywhere. Add a UV additive to the coolant and let it run for a while. Open the pressure valve to get it circulating. Then take a look around the bottom of the car and engine with the trays and bulkhead cover off first. You can see the water lines and the pump and most of the radiators that way. You can see the heat exchanger with the top engine cover off.

You'll also want to check the coolant tank for leaks.

Those are the very easy steps. The heater core comes out by removing the battery, windshield wipers, and all the plastic at the base of the windshield. It's not a hard job, but eliminate the easy ones first.

Don't buy anything until you know where the problem lies. Otherwise things will get expensive very quickly.