Heater core issue?

Troubleshooting a problem is never a waste of time.

A waste of time is throwing money at a problem without making sure what's wrong first.

I never said "throw money at it", but to check the hoses for leaks and then pull it.
Steamy window.
Trouble shooting done, because where the hell else is steam going to come from and get on the inside of the window?

Slobbery dog?
Wet, hot laundry in the back seat?
Over exited wife or girlfriend?

But yea go ahead and play with it for hours first, cause for some reason a lot of people on here love to do that.