<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 8:46 AM David Nock via Healeys <<a href="mailto:healeys@autox.team.net">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"><u></u>
<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.
<div> </div>
<div><br>
<div>
<div dir="ltr">Sent from my iPad</div>
<div dir="ltr"><br>
<blockquote type="cite">On Sep 17, 2025, at 12:13 PM, Robert
Markovich via Healeys <a href="mailto:healeys@autox.team.net" target="_blank"><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>
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<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"><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"> 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">www.britishcarspecialists.com</a></pre>
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