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If you are using the original style Bellow thermostat be sure that you
DO NOT use a higher pressure radiator cap. If you run a bellow
thermostat and a higher pressure cap the excess pressure will close the
thermostat once the cooling system gets up to temperature. Causing the
engine to overheat.
On 9/18/2025 1:15 PM, Simon Lachlan wrote:
> Hi,
> The original sleeved ones are - I think - easier to find in the UK.
> Certainly, I managed to find a few. I was advised that the Morgan
> people were a good source. I bought mine on eBay but that was a while
> ago. Simon
> Sent from my iPhone
>
>> On 18 Sep 2025, at 18:54, Harold Manifold <manifold@telus.net> wrote:
>>
>> 
>> Hi All,
>>
>> Thermostats and Healey cooling always generate interesting
>> discussions, and I'd like to clarify my previous comments on what
>> controls (or often doesn't control) the coolant temperature.
>>
>> To summarize some of the points made: Coolant flows down the
>> radiator, out the bottom hose, and into the water pump. It's then
>> pumped into the engine block's cooling jacket. The goal is to direct
>> the coolest fluid to the hottest part of the engine for optimal heat
>> transfer (i.e., the largest delta T). The coolant, having absorbed
>> heat, then moves up to the cylinder head, through the thermostat, and
>> back to the radiator. This process is known as thermosiphoning, where
>> heated coolant rises through the engine and falls as it cools in the
>> radiator.
>>
>> The heat generated by the engine is a function of the combustion
>> process (timing, carburation, etc.) and horsepower efficiency loss.
>> More horsepower output means more heat transferred to the coolant.
>> The radiator removes this heat, but its effectiveness is proportional
>> to the difference between the air and coolant temperatures.
>>
>> Assuming the radiator has sufficient capacity to remove heat, if the
>> coolant temperature the thermostat "sees" is less than its opening
>> temperature plus 20 degrees, the thermostat will slightly close to
>> restrict flow to the radiator. In this scenario, the thermostat is
>> actively controlling the coolant temperature. However, if the coolant
>> temperature exceeds 20 degrees above the thermostat's opening
>> temperature, then the coolant temperature is primarily a function of
>> the incoming air temperature, and the thermostat is no longer a
>> factor. In such cases, the coolant temperature is effectively
>> uncontrolled by the thermostat.
>>
>> To add to the discussion, the engine fan has minimal effect at speeds
>> greater than 15 miles per hour.
>>
>> Harold
>>
>> On Thu, Sep 18, 2025 at 8:46â?¯AM David Nock via Healeys
>> <healeys@autox.team.net> wrote:
>>
>> The thermostat does not control the high end temperature of the
>> engine. Its job is to get the engine up to an operating
>> temperature as soon as possible. Then in maintains the low end
>> temperature of the engine. Once the thermostat is open the engine
>> temperature is controlled by the radiator, radiator fan and air flow.
>>
>> On the 6 cylinder engine there is a sleeve attached to the
>> thermostat, that blocks off a bypass in the cylinder head. The
>> bypass is there to allow the coolant to flow when the thermostat
>> is closed. Once the thermostat is open the sleeve is there to
>> block the bypass allowing ALL the coolant to flow thru the radiator.
>>
>> David Nock
>>
>> British Car Specialists
>>
>>
>> On 9/17/2025 12:54 PM, Richard Mayor wrote:
>>> 165 is too cold for good running. Our engines run better in the
>>> 180 to 190 range.
>>>
>>> Sent from my iPad
>>>
>>>> On Sep 17, 2025, at 12:13â?¯PM, Robert Markovich via Healeys
>>>>
>>>>  165 is the one I use
>>>>
>>>>
>>>> Sent from the all new AOL app for iOS
>>>>
>>>> <https://aolapp.onelink.me/eG2g?pid=NativePlacement&c=US_Acquisition_YMktg_320_EmailSignature_AttributionDL&af_sub1=Acquisition&af_sub2=US_YMktg&af_sub3=&af_sub4=100002473&af_sub5=SentFromNewAOLApp__Interstitial_&af_ios_store_cpp=ce85ce34-ad0f-4811-a92b-a172743b064e&af_android_url=https%3A%2F%2Fplay.google.com%2Fstore%2Fapps%2Fdetails%3Fid%3Dcom.aol.mobile.aolapp%26listing%3Demail_signature_attribution>
>>>>
>>>> On Wednesday, September 17, 2025, 2:50 PM, Richard Antal via
>>>> Healeys <healeys@autox.team.net>
>>>>
>>>> Gents,
>>>> Â Â Â What is the desired coolant temperature for optimal
>>>> engine performance? I've searched the tech articles and can
>>>> find nothing that specifically answers that question. This
>>>> summer my BJ8 seemed to run fine with a 160 thermostat
>>>> which, according to the gauge which I've checked and found
>>>> to be accurate, kept the coolant at around 165. Thanks to
>>>> all who respond.
>>>> rich antal
>>>> _______________________________________________
>>>> Support Team.Net http://www.team.net/donate.html
>>>> Suggested annual donation $12.75
>>>>
>>>> Archive: http://www.team.net/pipermail/healeys
>>>> http://autox.team.net/archive/healeys
>>>>
>>>> Healeys@autox.team.net
>>>> http://autox.team.net/mailman/listinfo/healeys
>>>>
>>>> Unsubscribe/Manage:
>>>> http://autox.team.net/mailman/options/healeys/rmarkovich@aol.com
>>>>
>>>> _______________________________________________
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>>>> Suggested annual donation  $12.75
>>>>
>>>> Archive: http://www.team.net/pipermail/healeys
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>>>> http://autox.team.net/mailman/listinfo/healeys
>>>>
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>>>
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>>>
>>> Archive:http://www.team.net/pipermail/healeys
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>>>
>>>
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>> --
>> David Nock
>> British Car Specialists
>> Stockton Ca
>> 209 948 8767
>> www.britishcarspecialists.com <http://www.britishcarspecialists.com>
>>
>> _______________________________________________
>> Support Team.Net http://www.team.net/donate.html
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--
David Nock
British Car Specialists
Stockton Ca
209 948 8767
www.britishcarspecialists.com
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<p>If you are using the original style Bellow thermostat be sure
that you DO NOT use a higher pressure radiator cap. If you run a
bellow thermostat and a higher pressure cap the excess pressure
will close the thermostat once the cooling system gets up to
temperature. Causing the engine to overheat.</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 9/18/2025 1:15 PM, Simon Lachlan
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:092F24E8-280A-4EC3-B888-A3A259AB784F@alexarevel.plus.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
Hi,Â
<div>The original sleeved ones are - I think - easier to find in
the UK. Certainly, I managed to find a few. I was advised that
the Morgan people were a good source. I bought mine on eBay but
that was a while ago. Simon<br
id="lineBreakAtBeginningOfSignature">
<div dir="ltr">Sent from my iPhone</div>
<div dir="ltr"><br>
<blockquote type="cite">On 18 Sep 2025, at 18:54, Harold
Manifold <a class="moz-txt-link-rfc2396E"
href="mailto:manifold@telus.net";><manifold@telus.net></a> wrote:<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">
<div>Hi All,</div>
<div><br>
</div>
<div>Thermostats and Healey cooling always generate
interesting discussions, and I'd like to clarify my
previous comments on what controls (or often doesn't
control) the coolant temperature.</div>
<div><br>
</div>
<div>To summarize some of the points made: Coolant flows
down the radiator, out the bottom hose, and into the
water pump. It's then pumped into the engine block's
cooling jacket. The goal is to direct the coolest fluid
to the hottest part of the engine for optimal heat
transfer (i.e., the largest delta T). The coolant,
having absorbed heat, then moves up to the cylinder
head, through the thermostat, and back to the radiator.
This process is known as thermosiphoning, where heated
coolant rises through the engine and falls as it cools
in the radiator.</div>
<div><br>
</div>
<div>The heat generated by the engine is a function of the
combustion process (timing, carburation, etc.) and
horsepower efficiency loss. More horsepower output means
more heat transferred to the coolant. The radiator
removes this heat, but its effectiveness is proportional
to the difference between the air and coolant
temperatures.</div>
<div><br>
</div>
<div>Assuming the radiator has sufficient capacity to
remove heat, if the coolant temperature the thermostat
"sees" is less than its opening temperature plus 20
degrees, the thermostat will slightly close to restrict
flow to the radiator. In this scenario, the thermostat
is actively controlling the coolant temperature.
However, if the coolant temperature exceeds 20 degrees
above the thermostat's opening temperature, then the
coolant temperature is primarily a function of the
incoming air temperature, and the thermostat is no
longer a factor. In such cases, the coolant temperature
is effectively uncontrolled by the thermostat.</div>
<div><br>
</div>
<div>To add to the discussion, the engine fan has minimal
effect at speeds greater than 15 miles per hour.</div>
<div><br>
</div>
<div>Harold</div>
</div>
<br>
<div class="gmail_quote gmail_quote_container">
<div dir="ltr" class="gmail_attr">On Thu, Sep 18, 2025 at
8:46â?¯AM David Nock via Healeys <<a
href="mailto:healeys@autox.team.net";
moz-do-not-send="true"
class="moz-txt-link-freetext">healeys@autox.team.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div style="padding-bottom:1px">
<p>The thermostat does not control the high end
temperature of the engine. Its job is to get the
engine up to an operating temperature as soon as
possible. Then in maintains the low end temperature
of the engine. Once the thermostat is open the
engine temperature is controlled by the radiator,
radiator fan and air flow.</p>
<p>On the 6 cylinder engine there is a sleeve attached
to the thermostat, that blocks off a bypass in the
cylinder head. The bypass is there to allow the
coolant to flow when the thermostat is closed. Once
the thermostat is open the sleeve is there to block
the bypass allowing ALL the coolant to flow thru the
radiator. </p>
<p>David Nock</p>
<p>British Car Specialists</p>
<p><br>
</p>
<div>On 9/17/2025 12:54 PM, Richard Mayor wrote:<br>
</div>
<blockquote type="cite"> 165 is too cold for good
running. Our engines run better in the 180 to 190
range. Â
<div>Â </div>
<div><br>
<div>
<div dir="ltr">Sent from my iPad</div>
<div dir="ltr"><br>
<blockquote type="cite">On Sep 17, 2025, at
12:13â?¯PM, Robert Markovich via Healeys <a
href="mailto:healeys@autox.team.net";
target="_blank"
moz-do-not-send="true"><healeys@autox.team.net></a>
wrote:<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr"> 165 is the one I use<br>
<br>
<br>
<div><a style="font-size:12px"
href="https://aolapp.onelink.me/eG2g?pid=NativePlacement&c=US_Acquisition_YMktg_320_EmailSignature_AttributionDL&af_sub1=Acquisition&af_sub2=US_YMktg&af_sub3=&af_sub4=100002473&af_sub5=SentFromNewAOLApp__Interstitial_&af_ios_store_cpp=ce85ce34-ad0f-4811-a92b-a172743b064e&af_android_url=https%3A%2F%2Fplay.google.com%2Fstore%2Fapps%2Fdetails%3Fid%3Dcom.aol.mobile.aolapp%26listing%3Demail_signature_attribution";
target="_blank" moz-do-not-send="true">Sent
from the all new AOL app for iOS</a><br>
</div>
<br>
<p
style="font-size:15px;color:rgb(132,115,255);padding-top:15px;margin-top:0px">On
Wednesday, September 17, 2025, 2:50 PM,
Richard Antal via Healeys <a
href="mailto:healeys@autox.team.net";
target="_blank"
moz-do-not-send="true"><healeys@autox.team.net></a>
wrote:</p>
<blockquote>
<div
id="m_2673071501772592614yiv6324880639">
<div>
<div
style="font-family:"Helvetica
Neue",Helvetica,Arial,sans-serif;font-size:13px">
<div dir="ltr">Gents,</div>
<div dir="ltr">Â Â Â What is the
desired coolant temperature for
optimal engine performance? I've
searched the tech articles and can
find nothing that specifically
answers that question. This summer
my BJ8 seemed to run fine with a
160 thermostat which, according to
the gauge which I've checked and
found to be accurate, kept the
coolant at around 165. Thanks to
all who respond.</div>
<div dir="ltr">rich antal</div>
</div>
</div>
</div>
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<pre cols="72">--
David Nock
British Car Specialists
Stockton Ca
209 948 8767
<a href="http://www.britishcarspecialists.com"; target="_blank"
moz-do-not-send="true">www.britishcarspecialists.com</a></pre>
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<pre class="moz-signature" cols="72">--
David Nock
British Car Specialists
Stockton Ca
209 948 8767
<a class="moz-txt-link-abbreviated"
href="http://www.britishcarspecialists.com";>www.britishcarspecialists.com</a></pre>
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_______________________________________________
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