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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 8:46=E2=80=AFAM 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 t=
he
> 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 all=
ow
> 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 12:13=E2=80=AFPM, Robert Markovich via Healeys
> <healeys@autox.team.net> <healeys@autox.team.net> wrote:
>
> =EF=BB=BF 165 is the one I use
>
>
> Sent from the all new AOL app for iOS
> <https://aolapp.onelink.me/eG2g?pid=3DNativePlacement&c=3DUS_Acquisition_=
YMktg_320_EmailSignature_AttributionDL&af_sub1=3DAcquisition&af_sub2=3DUS_Y=
Mktg&af_sub3=3D&af_sub4=3D100002473&af_sub5=3DSentFromNewAOLApp__Interstiti=
al_&af_ios_store_cpp=3Dce85ce34-ad0f-4811-a92b-a172743b064e&af_android_url=
=3Dhttps%3A%2F%2Fplay.google.com%2Fstore%2Fapps%2Fdetails%3Fid%3Dcom.aol.mo=
bile.aolapp%26listing%3Demail_signature_attribution>
>
> On Wednesday, September 17, 2025, 2:50 PM, Richard Antal via Healeys
> <healeys@autox.team.net> <healeys@autox.team.net> wrote:
>
> Gents,
> 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 an=
d
> found to be accurate, kept the coolant at around 165. Thanks to all who
> respond.
> rich antal
> _______________________________________________
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> Archive: http://www.team.net/pipermail/healeys
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> Archive: http://www.team.net/pipermail/healeys http://autox.team.net/arch=
ive/healeys
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>
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oc@sbcglobal.net
>
> --
> David Nock
> British Car Specialists
> Stockton Ca
> 209 948 8767www.britishcarspecialists.com
>
> _______________________________________________
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>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div>Hi All,</div><div><br></div><div>Thermostats and Heal=
ey cooling always generate interesting discussions, and I'd like to cla=
rify my previous comments on what controls (or often doesn't control) t=
he coolant temperature.</div><div><br></div><div>To summarize some of the p=
oints 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 ja=
cket. The goal is to direct the coolest fluid to the hottest part of the en=
gine for optimal heat transfer (i.e., the largest delta T). The coolant, ha=
ving absorbed heat, then moves up to the cylinder head, through the thermos=
tat, and back to the radiator. This process is known as thermosiphoning, wh=
ere heated coolant rises through the engine and falls as it cools in the ra=
diator.</div><div><br></div><div>The heat generated by the engine is a func=
tion of the combustion process (timing, carburation, etc.) and horsepower e=
fficiency loss. More horsepower output means more heat transferred to the c=
oolant. The radiator removes this heat, but its effectiveness is proportion=
al to the difference between the air and coolant temperatures.</div><div><b=
r></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 activel=
y 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 temperatur=
e, and the thermostat is no longer a factor. In such cases, the coolant tem=
perature 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=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" clas=
s=3D"gmail_attr">On Thu, Sep 18, 2025 at 8:46=E2=80=AFAM David Nock via Hea=
leys <<a href=3D"mailto:healeys@autox.team.net";>healeys@autox.team.net</=
a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0p=
x 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u=
></u>
=20
=20
=20
<div style=3D"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.=C2=A0</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=3D"cite">
=20
165 is too cold for good running.=C2=A0 Our engines run better in the
180 to 190 range. =C2=A0
<div>=C2=A0</div>
<div><br>
<div>
<div dir=3D"ltr">Sent from my iPad</div>
<div dir=3D"ltr"><br>
<blockquote type=3D"cite">On Sep 17, 2025, at 12:13=E2=80=AFPM,=
Robert
Markovich via Healeys <a href=3D"mailto:healeys@autox.team.ne=
t" target=3D"_blank"><healeys@autox.team.net></a>
wrote:<br>
<br>
</blockquote>
</div>
<blockquote type=3D"cite">
<div dir=3D"ltr">=EF=BB=BF
165 is the one I use<br>
<br>
<br>
<div><a style=3D"font-size:12px" href=3D"https://aolapp.oneli=
nk.me/eG2g?pid=3DNativePlacement&c=3DUS_Acquisition_YMktg_320_EmailSign=
ature_AttributionDL&af_sub1=3DAcquisition&af_sub2=3DUS_YMktg&af=
_sub3=3D&af_sub4=3D100002473&af_sub5=3DSentFromNewAOLApp__Interstit=
ial_&af_ios_store_cpp=3Dce85ce34-ad0f-4811-a92b-a172743b064e&af_and=
roid_url=3Dhttps%3A%2F%2Fplay.google.com%2Fstore%2Fapps%2Fdetails%3Fid%3Dco=
m.aol.mobile.aolapp%26listing%3Demail_signature_attribution" target=3D"_bla=
nk">Sent from the all new AOL app
for iOS</a><br>
</div>
<br>
<p style=3D"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=3D"mailto:healeys@autox.team.net"; targe=
t=3D"_blank"><healeys@autox.team.net></a> wrote:</p>
<blockquote>
<div id=3D"m_2673071501772592614yiv6324880639">
<div>
<div style=3D"font-family:"Helvetica Neue",He=
lvetica,Arial,sans-serif;font-size:13px">
<div dir=3D"ltr">Gents,</div>
<div dir=3D"ltr">=C2=A0 =C2=A0 =C2=A0What is the desi=
red coolant
temperature for optimal engine performance? I'v=
e
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=3D"ltr">rich antal</div>
</div>
</div>
</div>
_______________________________________________<br>
Support Team.Net <a href=3D"http://www.team.net/donate.html=
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<br>
</blockquote>
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<fieldset></fieldset>
<pre>_______________________________________________
nk">http://www.team.net/donate.html</a>
Archive: <a href=3D"http://www.team.net/pipermail/healeys"; target=3D"_blank=
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</blockquote>
<pre cols=3D"72">--=20
David Nock
British Car Specialists
Stockton Ca =20
209 948 8767
<a href=3D"http://www.britishcarspecialists.com"; target=3D"_blank">www.brit=
ishcarspecialists.com</a></pre>
</div>
<u></u><u></u>
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_______________________________________________
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