Force India COO Otmar has said in F1 Show that at the CanadianGP they ran Merc engines revision 2 (old) but with revision 3 software as they weren't that concerns with reliability. Revision 3 engines will be installed at their scheduled time because they try to do 5 races per engine and it would be foolish to throw away still good engine for small performance uplift or risk of DNF.