Thermostats and Temperature Control Systems

[Scott Fisher <sefisher@xxxxxxxxx>]

Graham Hilder mentions that he's owned several cars that *did* run
colder when he removed the thermostat, and wonders if there's something
different about the 164.

I can't help him with the 164, but I can offer my New And Improved
Mental Model of what a thermostat does, learned by trying to "improve"
the cooling system on my daily-driver '83 Audi Coupe.  And since I
really learned about thermostats from an M.G. Midget, which uses the
same engine as Graham's BMC Mini (barring displacement -- mine was a
1275 -- and orientation in the chassis), I can talk about that as well. 
And yes, it *will* link up, at last, with Alfas.

My experience with the Audi was that it was running a little hot in the
hottest days of summer.  So I started with the old-time hot-rod tricks
that I'd done to my various old British sports cars: run straight water
with Water Wetter, something that's typically good for 20 degrees F on a
hot California summer's day.  (And no, I've never taken the thermostat
out, though I've installed cooler 'stats in most of my old sports cars
sooner or later.)  And the Audi's cooling fan was already stuck on (due
to a wonky thermoswitch), so I figured THAT had to help.

Well, it had exactly the reverse effect on the Audi -- the car ran
*hotter*, but paradoxically only at high speed.  That is, on the
freeway, where there was lots of air flow, the car would run hotter; if
I got stuck in traffic and sat still, the car would cool down.  This,
obviously, is exactly the opposite of my expectations.

So what I did... I returned the Audi to full factory specification
(including, BTW, replacing a coolant overflow cap which turned out to
have a leak in it, one that was only apparent when comparing it to a new
cap; I also replaced the coolant overflow hose, which was torn at the
hose clamps).  I also used the official Audi Factory Coolant (which is
*blue*, and phosphate-free), in roughly 40-60 coolant-water proportions.

It's perfect.  I can drive 70 mph in 100 degrees F and the temp gauge is
right in the middle.  The cooling fan comes on only when I'm stopped in
traffic, and then for typically 20-30 seconds at a time; I note that
there are two numbers stamped on the new fan switch, 90 C - 95 C, which
corresponds to the manual's comment that the fan is set to come on when
the coolant reaches 95 degrees and shut off when it drops to 90, so
we're seeing a VERY efficient radiator if it can drop 5 degrees C over
the entire volume in the core in some 20 seconds.

One final observation: on the Audi, the thermostat is in the water pump,
connected to the *bottom* hose of the radiator.  This, too, seemed
backwards at first, but it obviously works.

So... how does this concern the 164?

I had a flash of insight as I was troubleshooting the Audi, and this
insight may also have something to do with the 164, as well as Graham's
old Mini, I suspect:

After more than a decade and a half of working on hopelessly shot old
British sports cars, it was an entirely novel experience to work on a
car THAT HAD ACTUALLY BEEN DESIGNED BY PEOPLE WHO KNEW MORE ABOUT CARS
THAN I DO.

(And yes, my flashes of insight regularly have an element of the
smart-arse to them, something which should come as no surprise to anyone
who's known me for more than about, oh, three or four postings.)

Following this admittedly comic (but not entirely false) observation, I
also realized that in modern -- that is, post-emissions-control --
engines, it's not entirely correct to call it a "cooling system."  (And
Graham: I've owned a Mini, and it's not entirely correct to call THAT
thing a "cooling system" either, but for different reasons. :-)  It's a
*temperature control* system, designed to keep the engine operating
within a specific temperature range.  And this is a good thing, because
as long as you can keep the *intake* charge cool, performance and
economy (which are the same thing, of course) go up when the engine is
kept hot, and emissions drop as well.

So a modern "cooling" system is actually designed to keep the engine
operating *above* a certain minimum temperature, as well as below a
higher one.  And that, I'm convinced after weeks of pondering, is why
the thermostat in the Audi is in the *exit* line of the radiator -- it's
more precise to meter the flow of low-temperature coolant *into* the
block than it is to regulate the flow of high-temperature coolant *out*
of it.  Looked at that way, the response is "Well, DUH..."  If you want
to cool a room, you point the air conditioner *into* it, right?

What this all -- no, I won't say "boils down to," and aren't you glad of
that? -- sums up to is that modern cars are MUCH more complex systems
than the simple, rudimentary beasts that many of us enjoyed when we were
learning the way cars worked.  And while the following is a good axiom
for any car, it's critical for modern cars that when something isn't
right, the first thing to do is *put it back exactly the way the factory
engineered it*.  THEN go figure out where things aren't adequate for
your use, climate, or application.  

The 164, by definition, is a "modern" car.  So first, put it back the
way it's supposed to be.  And if THAT doesn't solve your problem, then
it's time for some methodical engineering -- NOT the haphazard removal
of components that may or may not have done the trick on engines
designed in the early 1950s (our beloved BMC A-series engines, for
example).

- --Scott Fisher

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End of alfa-digest V7 #127
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