Leaking pencil zinc plug

[fox islander]

Good morning everyone,
I recently noticed that my brass pencil zinc plug has a considerable leak. This of course is the brass plug that the zinc itself is screwed into...the whole assembly then screwed into the heat exchanger. I've tried tightening her up...it actually started leaking more. So here's my question....would threading the plug in with a wrap of teflon tape have any effect on the electrical connection required between the plug and Hx? I'm thinking the plug would still be electrically in contact with the Hx at the top of the threads....I'm hoping the tape would fill in the gaps between the plug and the threads. Still in search of that dry bilge.

Thanks

1990 C30 Mk ll
M-25XP

 

[hvbaker]

Yes, Teflon tape is a must.

 

[Stu Jackson]

Yes, Teflon tape is a must.

Absolutely incorrect. If you do this, the zinc will NOT work, because the teflon will INSULATE the zinc from the HX body.

What you need to do is remove the old zinc, then clean out the threads before reinstalling a new one.

 

[Don S/V ILLusion]

Stu
Would the fact the HX and zinc are both electrically connected by emersion in the same water obviate the lack of physical bond?

 

[Guts1236]

I'm not sure which engine you're talking about? My beta 25 has a pencil zinc at the backside of the heat exchanger. I replace mine every three months, and I had trouble the first time with water leaking. I use pipe dope it allows for metal to metal contact and seals the threads quite nicely. That's what I do every three months.

 

[Stu Jackson]

Stu
Would the fact the HX and zinc are both electrically connected by emersion in the same water obviate the lack of physical bond?

Don, what happens on the zincs on M25 series engine HXs is that if you isolate the zinc holder from the HX body, the zinc stays in great shape and the threads begin to disintegrate. Not the whole idea of using the zinc in the first place.

For those of you with Yanmar engines, the Universal zinc is in the HX ONLY, NOT on the engine.

 

[Don S/V ILLusion]

I don't get it but I'm sure you are correct.

 

[hvbaker]

Well, I don't know. My zinc get spent about every six months and I have never had a problem with my heat exchanger leaking or corroding.

 

[jrowan]

Don, you are correct that the zinc acts as an anode for corrosion, & will absorb corrosive properties of the water in which it is surrounded. The water flowing through the heat exchanger is indeed an electrolite & causes corrosion to everything it touches. Zincs do not prevent corrosion to the heat exchanger, they only slow corrosion as zinc is a very soft metal that naturally acts as an anode. Teflon tape can be used to stop the leak at the threads, & since the Teflon naturally tears when it is compressed by the wear of the pipe threads it will not prevent contact to the heat exhanger. But even if it s did, the water flowing around the zinc will still cause it to corrode.

 

[fox islander]

...thanks for the input. I'm going to use teflon. It makes sense to me that the thread ridges would still be in electrical contact with the Hx. B-t-w...I replace my pencil zinc once a year, at that cycle only about 10-20% looks gone.

 

[Stu Jackson]

B-t-w...I replace my pencil zinc once a year, at that cycle only about 10-20% looks gone.

Interesting. I only get three or four months out of my zincs. No teflon.

 

[Guts1236]

Interesting. I only get three or four months out of my zincs. No teflon.

Ditto when I take mine out it still has enough left on it that I can unscrew it and replace it with a new zinc after four months there is barely enough to grab on to. The only problem I see with using Teflon tape is it builds the thread up where pipe dope just seals between the threads. That's why I use pipe dope.

 

[hvbaker]

The zinc is acting as a sacrificial electrode in the local environment. It is participating in the oxidation reduction reaction. It reacts before the other metals in the same environment.

 

[damauney]

A electrical resistance check with a multimeter after new zinc installation would solve the question as to wether you have electrical continuity between the HX and plug regardless of what you us or don't use on the threads. A thought.

Good winds
DaveM