Posted for those interested in this saga. If not, ignore.

Yesterday, at the advice of the service manager at the dealership, I
called Nissan Customer Support, told them what was going on and was
issued a "case" number. I was told I'll receive a call sometime today
(Friday) from Nissan.

Meanwhile, this morning, I was nearby so I stopped in again at the
dealership with the intention of talking to the sales manager who makes
all the deals to make sure he was up to speed with what's going on. He
wasn't in but I talked to the second in command. The service manager
also came over to talk.

Bottom line is that as of yesterday Nissan instructed the dealership to
stop all work on trying to fix the problem. The regional Nissan "super
tech" who has been assisting in troubleshooting and the dealership tech
are both stumped. They have no idea what's wrong with the car. Then,
word came back from Nissan engineering that they suspect a bad engine
casting that is preventing proper coolant flow.

The dealership guys told me that when I talk to Nissan today, be polite
and professional as I've been with them but insist that you do *not*
want the car, even if they offer to install a new engine. They said
they are working to get Nissan to give me a replacement car of equal or
better value but it has to go through the "process" so nobody gets hurt
financially, including the dealership. He said they'll end up shipping
the one I bought back to Nissan engineering for a tear down to determine
what the actual problem is.

So, I'll wait for the phone call and comply with the next step.