[Healeys] Core plug query

[JSARCH]

Perhaps the thinking is draining the water will keep the system from being over pressurized and prevent hoses from rupturing?

 

John 

 

From: engl at accesscomm.ca <engl at accesscomm.ca> 
Sent: Monday, November 3, 2025 8:01 PM
To: healeys at autox.team.net
Cc: 'Bob Spidell' <bspidell at comcast.net>; 'JSARCH' <jmsdarch at sbcglobal.net>
Subject: RE: [Healeys] Core plug query

 

JSARCH is correct for many types of modern sprinkler heads, but there are still several types that use one form or another of fusible links.  I apologize for being a pedant on this topic (sorry, it is what I do – both being a pedant and design of automatic fire protection systems).

 

Mandatory Healey content : what is the advantage of draining the water from one’s cooling system if the engine is overheating?

 

Thanks.

 

Bob England

 

From: Healeys <healeys-bounces at autox.team.net <mailto:healeys-bounces at autox.team.net> > On Behalf Of JSARCH via Healeys
Sent: November 3, 2025 12:44 PM
To: 'Bob Spidell' <bspidell at comcast.net <mailto:bspidell at comcast.net> >; healeys at autox.team.net <mailto:healeys at autox.team.net> 
Subject: Re: [Healeys] Core plug query

 

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 <mailto: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 <mailto: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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