With my istp father, everyone is really clear about his emotions. Though he was, when I was a young boy not so forthcoming with his emotions, I now as an adult know what it was all about. He is Libra by sign and though I do not believe in those signs, his greatest wish is always harmony.
In my opinion, if you want to, you can get an istp to cry on you. But in that moment you maybe notice that you are totally out of line and have overstepped your boundaries. Cause from what I know from my father, he is one of the greatest Dads you can have.
Btw.: He always likes to say that he would have become an investment broker, if he had the chance (which he hadnt) and not a plumber. xD He runs his own plumbing company at the moment now for like 30 years and you can say, we are pretty rich

. But that investment broker thing reminds me of the MBTI and the close connection between istp and istj. Maybe J after all, is in fact something that comes with age.
Oh dear good that will make me entj. Hope I am wrong xD