The open circuit voltage reading will be higher on a cold engine.

I was reading 13.8-13.9 with the orig. alternator while testing a cold system.

This began to fall off as time went on so I decided to replace the alt. before it died. I installed a Bosch AL166X(100 amp) vs. the std. AL66X(80 amp) and now see approx. 14.3 at start-up first thing in the am.