It's safe to drive. However, if the core starts to leak bad, it could dump hot coolant (200 degree) in the passanger compartment.
As far as the problem, it does sound like the heater core. Is there a slimy film developing on the windshield? If so, that is from the coolant.
Finally, the heater core is going to cost around $150.00. The labor which is allowed for the job is 8.5 hours. Most of the dash needs to be removed and it's an involved job.
I hope that helps.
Tuesday, October 14th, 2008 AT 1:50 PM