the importance of thermostats

someone i know recently demonstrated that their modern function is
apparently poorly understood.

back in the day, a thermostat just sat on the high side of an engine,
and opened when the coolant temp convecting around it raised enough. if
there was a problem, like the thermostat failing closed, you could take
it out and the engine would simply run cold because it was like a faucet
that controlled the total coolant flow. and thus easy to understand.

but then came emissions regulation, and the need for closer engine
temperature management, so "bypass" cooling was introduced by some
manufacturers. i.e. there is a separate coolant circuit that flows in
parallel to the radiator which allows a much narrower band of engine
operating temp, and thus better control of emissions. it works by
introducing cooled fluid into what is actually the main circuit, so the
pump always has full flow, the engine has no hot spots, and management
is close. but, and this is apparently the part that's not so easy to
understand, if you run such a motor /without/ its thermostat [which
typically has a different configuration also btw*], you completely
unbalance the fluid dynamics and you can end up with only bypass flow
and consequently have no cooling.

this person i know has just blown their third [expensive] race engine
not understanding this so i repeat it here for the record. and if this
person is reading, and you're still hellbent on running without the
thermostat [which doesn't achieve what you want anyway] *block the
freakin' "bypass" circuit*!!!


*
<http://partimages.genpt.com/largeimages/974553.jpg>

vs.

<http://partimages.genpt.com/largeimages/974529.jpg>



--
fact check required

jim beam wrote:
> someone i know recently demonstrated that their modern function is
> apparently poorly understood.
>
> back in the day, a thermostat just sat on the high side of an engine,
> and opened when the coolant temp convecting around it raised enough. if
> there was a problem, like the thermostat failing closed, you could take
> it out and the engine would simply run cold because it was like a faucet
> that controlled the total coolant flow. and thus easy to understand.
>
> but then came emissions regulation, and the need for closer engine
> temperature management, so "bypass" cooling was introduced by some
> manufacturers. i.e. there is a separate coolant circuit that flows in
> parallel to the radiator which allows a much narrower band of engine
> operating temp, and thus better control of emissions. it works by
> introducing cooled fluid into what is actually the main circuit, so the
> pump always has full flow, the engine has no hot spots, and management
> is close. but, and this is apparently the part that's not so easy to
> understand, if you run such a motor /without/ its thermostat [which
> typically has a different configuration also btw*], you completely
> unbalance the fluid dynamics and you can end up with only bypass flow
> and consequently have no cooling.
>
> this person i know has just blown their third [expensive] race engine
> not understanding this so i repeat it here for the record. and if this
> person is reading, and you're still hellbent on running without the
> thermostat [which doesn't achieve what you want anyway] *block the
> freakin' "bypass" circuit*!!!
>
>
> *
> <http://partimages.genpt.com/largeimages/974553.jpg>
>
> vs.
>
> <http://partimages.genpt.com/largeimages/974529.jpg>

Interesting. I had not seen anything like thermo #1 before.
Thanks Jim.

On 9/12/2013 1:20 PM, Paul in Houston TX wrote:
> this person i know has just blown their third [expensive] race engine
> not understanding this so i repeat it here for the record.

That is not cool.

<whap>

--
T0m $herm@n

Paul in Houston TX > wrote in
:


>
> Interesting. I had not seen anything like thermo #1 before.
> Thanks Jim.



Both designs have been in use for decades.

"Bypass" cooling has been used since thermostats came into use, and well
before emissions controls were ever heard of: it's the only way you can get
a thermostat to open before the engine destroys itself.

Some systems left the bypass open all the time (#1; early '70s Toyota),
counting on the diametric difference between rad hose and bypass hose to
bias flow to the rad hose, and some systems used thermostats that blocked
the bypass once the thermostat opened (#2; early '70s Mazda), forcing 100%
of the flow through the thermostat.

Either design will experience overcooling when the thermostat is removed.

Concern for emissions -- specifically nitric oxide -- around 1990 resulted
in a major change in cooling-system design that had nothing to do with the
thermostat itself: The original U-shaped fluid path gave way to the
straight-line path that all engines have today. The reason for this change
is that the U-shaped path tended to cause the rear cylinder (bottom of the
U) to run hotter than the others, making it more difficult to control
emissions of nitric oxide; a straight-through path provides more-even
temperatures throughout the block.

--
Tegger

On 09/12/2013 05:47 PM, Tegger wrote:
> Paul in Houston TX > wrote in
> :
>
>
>>
>> Interesting. I had not seen anything like thermo #1 before.
>> Thanks Jim.
>
>
>
> Both designs have been in use for decades.

true.


>
> "Bypass" cooling has been used since thermostats came into use,

not true.


> and well
> before emissions controls were ever heard of:

nope. see above.


> it's the only way you can get
> a thermostat to open before the engine destroys itself.

absolute nonsense.


>
> Some systems left the bypass open all the time (#1; early '70s Toyota),
> counting on the diametric difference between rad hose and bypass hose to
> bias flow to the rad hose,

hardly any thermostat is open all the time. and they seldom rely simply
on "diametric difference".


> and some systems used thermostats that blocked
> the bypass once the thermostat opened (#2; early '70s Mazda), forcing 100%
> of the flow through the thermostat.

i don't know which mazda you have in mind, but ones i've seen, that's
not true. the whole point of a "bypass" system is that it is in fact,
the primary circuit that flows all the time, and the cooling circuit is
secondary - that works only when required.


>
> Either design will experience overcooling when the thermostat is removed.

absolutely not true. the whole point of my post was to illustrate
precisely that.


>
> Concern for emissions -- specifically nitric oxide -- around 1990

started being implemented in the 80's and researched in the 70's. your
integra is an example of that.


> resulted
> in a major change in cooling-system design that had nothing to do with the
> thermostat itself: The original U-shaped fluid path gave way to the
> straight-line path that all engines have today. The reason for this change
> is that the U-shaped path tended to cause the rear cylinder (bottom of the
> U) to run hotter than the others, making it more difficult to control
> emissions of nitric

nitrous.


> oxide; a straight-through path provides more-even
> temperatures throughout the block.

the kind of cooling circuit you describe is antiquated and dates back to
"convection only" cooling circuits, even though it continued to be used
until about the 70's. and nitrous emissions are the least of your
concerns with it.



--
fact check required

On Thu, 12 Sep 2013 09:41:54 -0700, jim beam > wrote:

>someone i know recently demonstrated that their modern function is
>apparently poorly understood.
>
>back in the day, a thermostat just sat on the high side of an engine,
>and opened when the coolant temp convecting around it raised enough. if
>there was a problem, like the thermostat failing closed, you could take
>it out and the engine would simply run cold because it was like a faucet
>that controlled the total coolant flow. and thus easy to understand.
>
>but then came emissions regulation, and the need for closer engine
>temperature management, so "bypass" cooling was introduced by some
>manufacturers. i.e. there is a separate coolant circuit that flows in
>parallel to the radiator which allows a much narrower band of engine
>operating temp, and thus better control of emissions. it works by
>introducing cooled fluid into what is actually the main circuit, so the
>pump always has full flow, the engine has no hot spots, and management
>is close. but, and this is apparently the part that's not so easy to
>understand, if you run such a motor /without/ its thermostat [which
>typically has a different configuration also btw*], you completely
>unbalance the fluid dynamics and you can end up with only bypass flow
>and consequently have no cooling.
>
>this person i know has just blown their third [expensive] race engine
>not understanding this so i repeat it here for the record. and if this
>person is reading, and you're still hellbent on running without the
>thermostat [which doesn't achieve what you want anyway] *block the
>freakin' "bypass" circuit*!!!

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. I would
think that it's possible.

On 09/12/2013 07:19 PM, Bill Vanek wrote:
> On Thu, 12 Sep 2013 09:41:54 -0700, jim beam > wrote:
>
>> someone i know recently demonstrated that their modern function is
>> apparently poorly understood.
>>
>> back in the day, a thermostat just sat on the high side of an engine,
>> and opened when the coolant temp convecting around it raised enough. if
>> there was a problem, like the thermostat failing closed, you could take
>> it out and the engine would simply run cold because it was like a faucet
>> that controlled the total coolant flow. and thus easy to understand.
>>
>> but then came emissions regulation, and the need for closer engine
>> temperature management, so "bypass" cooling was introduced by some
>> manufacturers. i.e. there is a separate coolant circuit that flows in
>> parallel to the radiator which allows a much narrower band of engine
>> operating temp, and thus better control of emissions. it works by
>> introducing cooled fluid into what is actually the main circuit, so the
>> pump always has full flow, the engine has no hot spots, and management
>> is close. but, and this is apparently the part that's not so easy to
>> understand, if you run such a motor /without/ its thermostat [which
>> typically has a different configuration also btw*], you completely
>> unbalance the fluid dynamics and you can end up with only bypass flow
>> and consequently have no cooling.
>>
>> this person i know has just blown their third [expensive] race engine
>> not understanding this so i repeat it here for the record. and if this
>> person is reading, and you're still hellbent on running without the
>> thermostat [which doesn't achieve what you want anyway] *block the
>> freakin' "bypass" circuit*!!!
>
> 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. I would
> think that it's possible.
>

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?

hint 1: the average radiator has a much greater surface area than the
average cylinder core.

hint 2: sufficient mass transfer with a small temp delta can out-cool
lower mass transfer with a higher temp delta.


--
fact check required

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

>On 09/12/2013 07:19 PM, Bill Vanek wrote:
>> On Thu, 12 Sep 2013 09:41:54 -0700, jim beam > wrote:
>>
>>> someone i know recently demonstrated that their modern function is
>>> apparently poorly understood.
>>>
>>> back in the day, a thermostat just sat on the high side of an engine,
>>> and opened when the coolant temp convecting around it raised enough. if
>>> there was a problem, like the thermostat failing closed, you could take
>>> it out and the engine would simply run cold because it was like a faucet
>>> that controlled the total coolant flow. and thus easy to understand.
>>>
>>> but then came emissions regulation, and the need for closer engine
>>> temperature management, so "bypass" cooling was introduced by some
>>> manufacturers. i.e. there is a separate coolant circuit that flows in
>>> parallel to the radiator which allows a much narrower band of engine
>>> operating temp, and thus better control of emissions. it works by
>>> introducing cooled fluid into what is actually the main circuit, so the
>>> pump always has full flow, the engine has no hot spots, and management
>>> is close. but, and this is apparently the part that's not so easy to
>>> understand, if you run such a motor /without/ its thermostat [which
>>> typically has a different configuration also btw*], you completely
>>> unbalance the fluid dynamics and you can end up with only bypass flow
>>> and consequently have no cooling.
>>>
>>> this person i know has just blown their third [expensive] race engine
>>> not understanding this so i repeat it here for the record. and if this
>>> person is reading, and you're still hellbent on running without the
>>> thermostat [which doesn't achieve what you want anyway] *block the
>>> freakin' "bypass" circuit*!!!
>>
>> 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. I would
>> think that it's possible.
>>
>
>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?
>
>hint 1: the average radiator has a much greater surface area than the
>average cylinder core.
>
>hint 2: sufficient mass transfer with a small temp delta can out-cool
>lower mass transfer with a higher temp delta.

When the ambient is about 115, there's a continuous sun load, and the
engine is under load, I can see it.

On 09/12/2013 08:20 PM, Bill Vanek wrote:
> On Thu, 12 Sep 2013 19:38:54 -0700, jim beam > wrote:
>
>> On 09/12/2013 07:19 PM, Bill Vanek wrote:
>>> On Thu, 12 Sep 2013 09:41:54 -0700, jim beam > wrote:
>>>
>>>> someone i know recently demonstrated that their modern function is
>>>> apparently poorly understood.
>>>>
>>>> back in the day, a thermostat just sat on the high side of an engine,
>>>> and opened when the coolant temp convecting around it raised enough. if
>>>> there was a problem, like the thermostat failing closed, you could take
>>>> it out and the engine would simply run cold because it was like a faucet
>>>> that controlled the total coolant flow. and thus easy to understand.
>>>>
>>>> but then came emissions regulation, and the need for closer engine
>>>> temperature management, so "bypass" cooling was introduced by some
>>>> manufacturers. i.e. there is a separate coolant circuit that flows in
>>>> parallel to the radiator which allows a much narrower band of engine
>>>> operating temp, and thus better control of emissions. it works by
>>>> introducing cooled fluid into what is actually the main circuit, so the
>>>> pump always has full flow, the engine has no hot spots, and management
>>>> is close. but, and this is apparently the part that's not so easy to
>>>> understand, if you run such a motor /without/ its thermostat [which
>>>> typically has a different configuration also btw*], you completely
>>>> unbalance the fluid dynamics and you can end up with only bypass flow
>>>> and consequently have no cooling.
>>>>
>>>> this person i know has just blown their third [expensive] race engine
>>>> not understanding this so i repeat it here for the record. and if this
>>>> person is reading, and you're still hellbent on running without the
>>>> thermostat [which doesn't achieve what you want anyway] *block the
>>>> freakin' "bypass" circuit*!!!
>>>
>>> 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. I would
>>> think that it's possible.
>>>
>>
>> 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?
>>
>> hint 1: the average radiator has a much greater surface area than the
>> average cylinder core.
>>
>> hint 2: sufficient mass transfer with a small temp delta can out-cool
>> lower mass transfer with a higher temp delta.
>
> When the ambient is about 115, there's a continuous sun load, and the
> engine is under load, I can see it.

you can see reduced delta, but that doesn't change the equation because
it would be common to both circumstances. the point is, faster flow
doesn't stop the engine cooling, it's misdirection of that flow that
causes problems - it's two circuits and no valve directing how much
flows in each one.


--
fact check required

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