Thermostats

[graham.hilder@xxxxxxxxxxxxx (Graham Hilder)]

More queries on whether a car with a removed or stuck open
thermostat will overheat or underheat, and why.  

Firstly, re Scott's experience  (Digest no. 127) with the Audi which
overheated while moving fast through the air but cooled when
stuck in a jam, this was an intriguing effect, but I'm not sure that it
relates to the above issue. If I read Scott correctly, this car didn't
have a removed thermostat, and apparently the thermostat didn't
enter into his Audi process at all.  I could be wrong though.

Next, Scott observed that the "cooling system" should really be
thought of as a "temp control system", designed to keep the
engine temp within a specific range, and not just to cool it
willy-nilly. On this, I totally agree, and I shouldn't think there's
been any suggestion to the contrary. After all, if it were just an
open-loop cooling system it would never have included a t-stat or
other control device at all, so there's no argument there, over the
object of the system.
But (unlike Scott, I think), I would suggest that this must also
apply to an old Mini for example, and not only to modern engines
as I believe Scott was suggesting. I suggest that that the old Min
and the new 164 both have t-stats and both for the same reason,
i.e. to maintain a specific desired temp.   Nothing's changed there.

I feel the original issue still hasn't been settled, i.e. when a t-stat is
removed or stuck open, does the car run too hot or too cool, and if
too hot, then why?   I must note that for me this is only an
academic question, because I wouldn't dream of ripping out a
thermostat myself to cure an overheating problem; this is
definitely the wrong approach, as Scott said.  No, I'm only asking
about the effects of removed or stuck open t-stats because each
of the cars which have been in that sorry state when I acquired
them have run cold, and have run at the correct (higher) temps
with the t-stat restored, whereas the 164 apparently does the
opposite (no t-stat = hot running).  I was interested, academically
only, to find out why. Fred's answer was that removing the t-stat
reduced flow restriction which increased flow rate which caused
hotter running since radiator couldn't extract as much heat from
the faster flowing coolant. I had two problems with this :

(a) Firstly, it requires us to agree that as flow increases, the
radiator heat extraction increases up to a point, but if the flow is
further increased then the curve reverses, and the radiator now
starts to extract less heat. Does this seem natural?  (As the
engine's thermostat opens, and increases flow, it seems clear that
heat extraction increases, to stop further temp rise; so why would
this extraction-trend suddenly reverse if flow is increased a bit
further by a removed or stuck fully open t-stat?).

(b) My next difficulty was, if the "no thermostat=hot running"
effect occurs in a 164, why did it not occur in the various cars I've
acquired with no or open t-stats?  (Including mid-60s Mini,
late-70s 116 Giulietta, early-80s Alfa Sud). I wouldn't have thought
that the flow and heat transfer laws of a 164 radiator were all that
much different from the rads in my examples, and so, if Fred's
explanation holds for a 164 rad then I'd think it should have
applied equally to my old bangers.... but it didn't: they ran cold.

For these reasons, I still think there's something else or something
more to be explained about the 164 overheating when it had no
t-stat.  Academic interest only, but interesting nonetheless.
(Better than cupholders, anyway). 

Best regards,
Graham H,
N.Z. 

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