On Thu, 29 Jun 2017 13:32:34 -0400, "Mr. Luddite"
wrote:

How do they control the heat if the front is hot water?


I don't know. All I was told was that my theory had merit up to the
2016 model year. The design was changed in 2017 and the "Heat Control
Valve" that I suspected is no longer used. The rear heat is now
electric, eliminating the plumbing to a second heater core.

I understand that the rear heat is electric but they would not have
replaced an engine to fix an electrical problem so the front must be
hot water. That is really the only practical way to get heat into a
car anyway since a typical full size car heater core is about 24,000
BTU when the engine is at operating temperature.
That is 7 KW of power. (almost 600 amps at 12v)

I can understand that they probably get away with smaller heaters
these days but that is what the good old "GM heater" was in the olden
days and what you wanted if it was really cold outside. It does give
you a sense of scale tho. Even if they just have 1-2-1.4kw of heat (a
big hair dryer or a plug in space heater) it is still ~100 amps.

This is why sometimes an "older design" is also a more mature design
that has the benefit of having all the bugs worked out. I used to call
it the "not invented here" syndrome when I had my company. For some
reason engineers .... and it was usually the mechanical types ... were
never satisfied with a previous and proven design of something if they
didn't have a hand in it's original development. Since they didn't
"invent it" they always wanted to modify or change it. I had to
implement a standing order that if the design of some component of the
thin film deposition systems we built wanted to be changed by
engineering, it required a design review meeting that included me where
the engineer or designer was given the opportunity to pitch his or her
case for the change. One of the critical issues was the hinges for the
big chamber doors. The doors could weigh a couple of tons and the hinge
itself had to allow a certain amount of articulation to allow the door
to easily seal to the chamber flange O-ring. Without the articulation
the hinge side of the door would scuff across the O-ring causing
premature wear and making the door difficult to close. It took a while
to work out a good design but the engineers and designers often tried to
"improve" it.

I know all about "NIH". We used to have that fight between plants.
The "air cooled" guys at Endicott always ignored and dismissed any
idea that came from Kingston Poughkeepsie (water cooled)
The GSD plant in Rochester was like a different company (S/36 AS/400)
They didn't do anything the same.