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--></style></head><body lang=EN-US link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>More often than not, automatic fire sprinklers are activated by a glass bulb filed with a liquid that expands and breaks the bulb which then opens the fire sprinkler head. Bismuth is used in fusible links which that melt at certain temperatures to activate automatic fire doors.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Healeys <healeys-bounces@autox.team.net> <b>On Behalf Of </b>Bob Spidell via Healeys<br><b>Sent:</b> Friday, October 31, 2025 11:13 AM<br><b>To:</b> healeys@autox.team.net<br><b>Subject:</b> Re: [Healeys] Core plug query<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>I did a little diggin ... <br><br>Apparently, they are designed to melt if the engine overheats, which would be grounds for voiding the warranty on a re-man. I wonder if the plug is made of bismuth, which is what sets off automatic fire sprinklers.<br><br><a href="https://www.toyotanation.com/threads/mysterious-plugs-in-engine-block.1659464/">https://www.toyotanation.com/threads/mysterious-plugs-in-engine-block.1659464/</a><o:p></o:p></p><div><p class=MsoNormal>On 10/31/2025 5:08 AM, Simon Lachlan via Healeys wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p><span lang=EN-GB> I saw this on Facebook just now. Just curious….what’s that thing in the middle of the core plug? And, if it’s a good thing, why don’t all the plugs have one? </span><o:p></o:p></p><p><span lang=EN-GB>Thanks, Simon</span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></blockquote></div></body></html>