[Healeys] Core plug query

[JSARCH]

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.

 

From: Healeys <healeys-bounces at autox.team.net> On Behalf Of Bob Spidell via Healeys
Sent: Friday, October 31, 2025 11:13 AM
To: healeys at autox.team.net
Subject: Re: [Healeys] Core plug query

 

I did a little diggin ... 

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.

https://www.toyotanation.com/threads/mysterious-plugs-in-engine-block.1659464/

On 10/31/2025 5:08 AM, Simon Lachlan via Healeys wrote:

 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? 

Thanks, Simon

 

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