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Re: Re-Re- head temps
RDH wrote "The design, placing the thermostat in the water intake from the
radiator rather than the head outlet leads to rather wide temp swings (and is
downright crinimally stupid and incompetent, in my opinion)."
I disagree. This is another one of those tradeoffs that can be argued either
way. As long as the thermostat is not backwards, the sensing side of it is
in the path of mixed coolant entering the water pump, regulating the coolant
temperature going INTO the engine. On the other hand, putting the thermostat
at the head outlet would regulate the temperature of coolant LEAVING the
engine. So it would seem that sensing the coolant temperature at the head of
an Audi would naturally read higher than the thermostat set temperature.
And, this temperature difference would certainly be load dependant since the
coolant temperature must rise as it absorbs varying amounts of heat from the
engine. If you are seeing what you belive to be an excessive rise in coolant
temperature under full load, there may be some restriction in the block/head,
a bad water pump, or some weird coolant mix problem with inadequate heat
capacity. I am assuming your radiator is doing its job and the thermostat is
not max'ed out.
I can't honestly think of any real advantage to putting the thermostat at the
intake side except for ensuring it is completely submerged in coolant despite
a possible low coolant situation. In all likelihood, it was just a
Hmm...hadn't thought of that one...
convenient location for the design engineers to put it, and a way to ensure
more Autobahn antifreeze sales when changing thermostats. :-)
Well, the head is the where the red-hot exhaust valves are getting
red-hot, ditto the red-hot exhaust manifold, and where, with the
exception of the piston head, the major "impact" of combustion takes
place. And all this on an "alloy" piece. [I *think* that "aluminum/
alloy" is generally more tem- perature-sensitive, and more subject to
damage with inadequate cooling.]
The head is where the temp is gonna rise *FAST and HARD*. Putting it
as far away as possible from any possible [increased] coolant seems
highly contra-intuitive. By having the thermostat in the head (at
the coolant outlet), when the head suddenly gets very hot, the
thermostat is right there and can immediately open up, allowing more
coolant to flow *right now*, without having to wait until enough heat
from the head percolates its way down to the block and eventually out
to the thermostat . . .
It just "seems to make sense" that you would regulate the temperature
where the temperature is the worst/hottest/most-important/most-dangerous,
which is the head, right?
I guess to take my thinking to its logical conclusion, it seems like
'twould be best if the coolant *flow* was reversed, coming in at the
head and then flowing thru the block and out to the radiator . . .
(you would be "pumping heat downhill", which seems somehow wrong -- I
remember when the DEC engineers discovered that just reversing the fans
in the huge KL-10 racks to exhaust out the top [sucking in cool air at
the bottom, following nature's own heat path: "heat rises"] made a sub-
stantial improvement in cooling that ECL monster! although I think air
vs "water" as the coolant medium makes all difference in this case).
Of course then you'd have to sandwich the thermostat between the block
and the head - ug!
I know - relays! Yes, RELAYS! we can install a bunch of thermoswitchs
controlling a rack of relays to govern an electric water pump. We could
up the relay count substantially, not to mention at least 30 feet of
undergauge wiring to melt, and at least 20 new crimp connectors . . .
Just think, you won't have to worry about idle/cooldown of a hot and
stressed engine anymore, run it hot and shut it off, and then be enter-
tained by the cacophony of relays chattering to themselves cycling pumps,
fans, blowers (can't forget the injector cooling fans, now can we), and
Good thing this is Friday . . .