Is it safe to use crisco that is at least 1 ½ years old in a pie crust? How can I tell if it has gone bad?

You'll be able to tell if it's rancid if it smells bad (which will be very obvious!)—don't use it if so! The shelf life of Crisco is about a year.

Also, here's how to read their labeling: http://www.crisco.com/about_crisco/faqs.aspx#faq_bestused