I'm sorry. I didn't answer your entire question. Without seeing how bad it is cracked, I can't tell you how long it will it will last. As far as safety, there is a chance of carbon monoxide getting into the passanger compartment and poisoning you. I don't mean to scare you, but that is a fact.
Let me know if you have other questions.
Saturday, May 22nd, 2010 AT 11:58 PM