New heater core but now white smoke?

K so I replaced my heater core. But now every time I turn the heat on I get white smoke from the vents. Any ideas?

Coolant in heater core. Maybe just some coolant on the outside part, or a leak.

So there's coolant in the housing?

"Something" is volatilizing, that's the white smoke. If just turning on the fan does not produce the smoke, then must be from the heater core getting hot. Maybe it's on the outside and will burn off.

Take a spray bottle with rubbing alcohol in it and run the engine and spray the alcohol into the intake of the heater. It will get all the stuff out eventually.

Does the smoke (or is it steam?) appear as soon as the cold engine is started and heater/fan turned on? If not until the engine is warm, the heater core probably has a water leak.
Or can be protective coating on the new core, which will stop. Run it, see if the radiator gets low, then it is a leak. There should eventually be a puddle under the truck, like the a/c is working (that puddle is from moisture condensed from the air, water when the a/c is not used- heater core)