the importance of thermostats

On Thu, 12 Sep 2013 19:38:54 -0700, jim beam > wrote:

>
>so, [logical thinking exercise] if it's running through the radiator too
>fast to dump heat, how is it running through the engine slow enough to
>pick up heat in the first place?
>

For typical engine cooling (not the bypass method you mentioned) logic
says the more flow the more heat transfer, the cooler the engine runs.
You're not going to get turbulence from the typical water pump that
would lessen heat transfer.
So unless he's talking about something "atypical," That GM engineer
was just wrong. Maybe he's a suspension engineer.

It's all good to point out any "bypass" cooling that would overheat an
engine with the thermo removed. How about some examples of brands?

Personally, I've run a couple of old cars without thermos.
But I was ignorant. And it probably did little harm.
But it's been a long, long time since I learned that modern engines
are designed to operate best within a certain temp range.
So I would do all I could to avoid running without the specified
thermo.

But I didn't know about this bypass system in any car I'm familiar
with (not many). So I wouldn't expect overheating by removing the
thermo.

"Tegger" > wrote in message
...
> Bill Vanek > wrote in
> :
>>
>> One day when I was working on some related issue, I talked to a GM
>> engineer, and he told that running without a thermostat could indeed
>> overheat the engine, but his explanation was that the coolant would
>> move through the radiator too quickly for it to cool properly.
>
> It's not true. Any reasonably-modern engine will UNDERHEAT without its
> thermostat. Go ahead, try it yourself. I have.
>
> Tegger

Some here, not you, do not understand the principle of flow
in parallel circuits. The resultant resistance (and accordingly
the flow) follows the rule of the reciprocal of the sum of the
reciprocals. One way though that overheatring can result
from an absence of a thermostat is hose collapse on the
suction side, caused by increased flow rate. A spring in
the hose can be one method of preventing that problem.

On 09/13/2013 06:14 AM, . wrote:
> "Tegger" > wrote in message
> ...
>> Bill Vanek > wrote in
>> :
>>>
>>> One day when I was working on some related issue, I talked to a GM
>>> engineer, and he told that running without a thermostat could indeed
>>> overheat the engine, but his explanation was that the coolant would
>>> move through the radiator too quickly for it to cool properly.
>>
> > It's not true. Any reasonably-modern engine will UNDERHEAT without its
>> thermostat. Go ahead, try it yourself. I have.
>>
>> Tegger
>
> Some here, not you, do not understand the principle of flow
> in parallel circuits. The resultant resistance (and accordingly
> the flow) follows the rule of the reciprocal of the sum of the
> reciprocals.

using an electrical analogy for fluid flow is way too simplistic. there
are some very rudimentary parallels at low flow rates, but because
fluids have mass, they have momentum, and they also experience
turbulence and cavitation. all three factors can completely obliterate
any simplistic "electrical" analogy - venturi effect for example.


> One way though that overheatring can result
> from an absence of a thermostat is hose collapse on the
> suction side, caused by increased flow rate. A spring in
> the hose can be one method of preventing that problem.

not a differentiator - can happen with any pumped system.


--
fact check required

On 09/13/2013 04:52 AM, Tegger wrote:
> Bill Vanek > wrote in
> :
>
>>
>> One day when I was working on some related issue, I talked to a GM
>> engineer, and he told that running without a thermostat could indeed
>> overheat the engine, but his explanation was that the coolant would
>> move through the radiator too quickly for it to cool properly.
>
>
>
> It's not true. Any reasonably-modern engine will UNDERHEAT without its
> thermostat. Go ahead, try it yourself. I have.

????

<https://groups.google.com/forum/#!original/rec.autos.tech/QyC6zDESXsU/8rcrUcM4AHEJ>


--
fact check required

On 09/13/2013 06:00 AM, Vic Smith wrote:
> On Thu, 12 Sep 2013 19:38:54 -0700, jim beam > wrote:
>
>>
>> so, [logical thinking exercise] if it's running through the radiator too
>> fast to dump heat, how is it running through the engine slow enough to
>> pick up heat in the first place?
>>
>
> For typical engine cooling (not the bypass method you mentioned) logic
> says the more flow the more heat transfer, the cooler the engine runs.
> You're not going to get turbulence from the typical water pump that
> would lessen heat transfer.
> So unless he's talking about something "atypical," That GM engineer
> was just wrong. Maybe he's a suspension engineer.
>
> It's all good to point out any "bypass" cooling that would overheat an
> engine with the thermo removed. How about some examples of brands?
>
> Personally, I've run a couple of old cars without thermos.
> But I was ignorant. And it probably did little harm.
> But it's been a long, long time since I learned that modern engines
> are designed to operate best within a certain temp range.
> So I would do all I could to avoid running without the specified
> thermo.
>
> But I didn't know about this bypass system in any car I'm familiar
> with (not many). So I wouldn't expect overheating by removing the
> thermo.

indeed, it's entirely engine specific.

as to brands, the honda 4-bangers are big into the bypass thing. but my
old 22r toyota is not. if you look at the pics of the two thermostats i
posted before, you'll note the secondary diaphragm on one of them. that
helps control the secondary circuit flow on a honda bypass circuit.


--
fact check required

Vic Smith > wrote in
:

> On Thu, 12 Sep 2013 19:38:54 -0700, jim beam > wrote:
>
>>
>>so, [logical thinking exercise] if it's running through the radiator too
>>fast to dump heat, how is it running through the engine slow enough to
>>pick up heat in the first place?
>>
>
> For typical engine cooling (not the bypass method you mentioned) logic
> says the more flow the more heat transfer, the cooler the engine runs.




You're correct in that higher flow /does/ result in better heat-transfer.

The thing that improves heat-transfer the most is the "temperature
gradient", which is the temperature difference between the warmer (water)
and the cooler (air) sides. The greater the difference, the /steeper/ the
gradient; the greater the difference, the greater the transfer of heat.

Think of a playground slide: the steeper the slide, the faster your kid
goes down it, and the geater the number of kids that can go down the slide
for any given time interval. The /flatter/ the slide, the slower the kids
go down, and the fewer the number of children that can follow each other
down for any given time interval.

Modern cooling systems are designed to operate with a steep gradient, but
one that gets flattened a bit by the thermostat when necessary. Remove the
thermostat, and the gradient /steepens/, resulting in even /better/ heat-
rejection into the atmosphere. Eventually you get too much of a good thing.




> You're not going to get turbulence from the typical water pump that
> would lessen heat transfer.



Turbulence /improves/ heat-transfer. The more turbulence the better.
Turbulence can be effected by applying a texture to the solid surfaces, or
by increasing fluid-flow, or both.

Turbulence strips away the boundary layer that tends to form between solid
surfaces and cooling fluid. The boundary layer acts as a sort of
insulation. Insulation works by flattening the temperature gradient, which
results in /less/ heat transfer.

It is true that an always-open bypass can affect heat-rejection by allowing
some of the heat to recirculate back into the engine, but that would
actually eventually /steepen/ the gradient at the rad/air interface,
canceling any deleterious effect of the open bypass. However, an open
bypass results in less precise control over cooling system operation.In any
case, an open bypass certainly does NOT cause overheating.


--
Tegger

On 09/13/2013 03:35 PM, Tegger wrote:
> Vic Smith > wrote in
> :
>
>> On Thu, 12 Sep 2013 19:38:54 -0700, jim beam > wrote:
>>
>>>
>>> so, [logical thinking exercise] if it's running through the radiator too
>>> fast to dump heat, how is it running through the engine slow enough to
>>> pick up heat in the first place?
>>>
>>
>> For typical engine cooling (not the bypass method you mentioned) logic
>> says the more flow the more heat transfer, the cooler the engine runs.
>
>
>
>
> You're correct in that higher flow /does/ result in better heat-transfer.
>
> The thing that improves heat-transfer the most is the "temperature
> gradient", which is the temperature difference between the warmer (water)
> and the cooler (air) sides. The greater the difference, the /steeper/ the
> gradient; the greater the difference, the greater the transfer of heat.

in order to cool, you do indeed need a temperature delta. however, a
"steep" gradient indicates an insulator and thus little cooling.


>
> Think of a playground slide: the steeper the slide, the faster your kid
> goes down it, and the geater the number of kids that can go down the slide
> for any given time interval. The /flatter/ the slide, the slower the kids
> go down, and the fewer the number of children that can follow each other
> down for any given time interval.

too simplistic.


>
> Modern cooling systems are designed to operate with a steep gradient,

you mean high transfer.


> but
> one that gets flattened a bit by the thermostat when necessary. Remove the
> thermostat, and the gradient /steepens/, resulting in even /better/ heat-
> rejection into the atmosphere. Eventually you get too much of a good thing.

transfer rate increases. you can have a high heat transfer rate with a
low temperature delta, if the mass transfer rate is high. that's how
the fan on a car radiator works - you step up the mass transfer rate to
increase the heat transfer rate. it's important to understand that you
can't "increase" a temperature delta to assist cooling - atmospheric
temperature is whatever it is.


>
>
>
>
>> You're not going to get turbulence from the typical water pump that
>> would lessen heat transfer.
>
>
>
> Turbulence /improves/ heat-transfer.

increased flow improves heat transfer. turbulence, by definition,
contains random elements that can upset transfer.


> The more turbulence the better.
> Turbulence can be effected by applying a texture to the solid surfaces, or
> by increasing fluid-flow, or both.

increased flow. texture increases surface area - another factor entirely.


>
> Turbulence strips away the boundary layer

turbulence can thicken it.
<http://www.grc.nasa.gov/WWW/BGH/boundlay.html>


> that tends to form between solid
> surfaces and cooling fluid. The boundary layer acts as a sort of
> insulation. Insulation works by flattening the temperature gradient,

conductors flatten the gradient, insulators increase it. if you have no
gradient, then everything is isothermal.


> which
> results in /less/ heat transfer.

delta, not gradient.


>
> It is true that an always-open bypass can affect heat-rejection by allowing
> some of the heat to recirculate back into the engine,

right. because it's short-circuiting the radiator.


> but that would
> actually eventually /steepen/ the gradient at the rad/air interface,

doesn't mean there's heat transfer. if it's insulated, you have an even
bigger delta, but there's no cooling.


> canceling any deleterious effect of the open bypass. However, an open
> bypass results in less precise control over cooling system operation.In any
> case, an open bypass certainly does NOT cause overheating.

an open bypass that short-circuits flow through the heat exchanger, the
radiator, will most definitely cause overheating.


--
fact check required

On 2013-09-14, jim beam > wrote:

> too simplistic.

Try this:

http://www.wiley.com/WileyCDA/WileyT...HEP001604.html

On 09/14/2013 01:31 PM, Brent wrote:
> On 2013-09-14, jim beam > wrote:
>
>> too simplistic.
>
> Try this:
>
> http://www.wiley.com/WileyCDA/WileyT...HEP001604.html
>

thanks, i already have one.


--
fact check required

On 2013-09-15, jim beam > wrote:
> On 09/14/2013 01:31 PM, Brent wrote:
>> On 2013-09-14, jim beam > wrote:
>>
>>> too simplistic.
>>
>> Try this:
>>
>> http://www.wiley.com/WileyCDA/WileyT...HEP001604.html
>>
>
> thanks, i already have one.

I doubt it.