how do u know when your heater core is going bad

 

You smell it when you turn the vents on, mostly with heat on, more than normal moisture on the windshield when running, and you'll normally find excess coolant in the heater box to drain from the passenger side firewall in the engine bay. You may also find a wet floor board

 

^^^^What he said and if you have a nose for coolant you will smell it before anything else.

 

it leaks, plain and simple, and out the evap drain hole it rolls

 

Either it leaks or it gets clogged (no heat)

 

Or you're riding shotgun and you get hot coolant all over your legs.

 

^ normally you'll know before that happens since the heater box will drain

 

I'm saying from real life experience.