This was a fairly straightforward diagnosis, the root cause was something I've never seen before. Upper hose wouldn't get above 130F idling in the shop. Sold a thermostat & gasket, then found this:
Definitely a candidate for the 'Eye spy' section in a monthly, local, automotive service magazine.
Hey Mike. And of course the customer never mentioned anything about having a thermostat installed prior to bringing the vehicle to your shop.
Not a word, though it looked like it had been there for a while.