will genius bar do a free diagnostics on a macbook pro out of warranty

Yes, absolutely.

In or out of warranty you can get a free over the counter 'Apple Service Diagnostics' test

Genius reservation http://www.apple.com/retail/geniusbar/

on-line https://getsupport.apple.com/GetproductgroupList.action

check warranty https://selfsolve.apple.com/agreementWarrantyDynamic.do

The genius will test your Mac for free, and talk to you about what you think the problem might be. They sometimes do "no parts required" repairs for you if they can. (example: remove a stuck CD, no charge).

They will work with you as long as required, but their attention may not be exclusive to you. (example: There may be another customer there who has been running a long re-install who needs the genius attention again for a while.)

All Genius Bar Appointment are free.

They will test your MacBook and tell you what's wrong with your system and cost to repair.