should zinc screwins be caulked?

[sailingdeacon]

My Universal m35 has a pencil zinc in the heat exchanger. When I change it there has always been a drip, so I had to put some caulk on the threads. Recently I had some galvanic action occur on a new water pump (part of the raw water system with the heat exchanger). The zinc showed some wear but perhaps not as much as usual. Is there a danger that the caulk would prevent a good electrical connection? Or why am I getting a leak in the first place?

 

[mherrcat]

I need to check my heat exchanger zinc as well. It looks like there is teflon tape on the exposed threads that I can see.

 

[treilley]

You would still get a decent electrical connection with any type of caulk but the proper method is to use teflon tape as Mherrcat has stated.

 

[sailingdeacon]

I would much prefer Teflon tape but my first attempts with teflon showed me it will take quite a number of rounds to stop the leak. (have not completed the job yet). But I feared that the teflon tape, if it stopped the leak would prevent the good connection. Or does it sort of tear up as it tightens?

The mechanic who looked at the pump felt it was electrolosis and it was only 8 months old. Parts were replaced at no charge by the Sherwood dealer.
The zinc that was in it had no more caulk than previously... in fact I let the old seal continue to work with no new caulk.

 

[mherrcat]

Maybe you could try Rectorseal. I used it on my fuel tank fittings and it seems to be working fine.

 

[treilley]

That zinc should have pipe threads which get tighter the further you screw it in. Unless it has been cross threaded or damaged in some other way, it should seal without any sealant. The teflon tape is more for ease of removal than anything.

 

[Glyn Judson]

Getting electrical conductivity.

All, I can't speak the the need of a zinc having conductivity to the block but can tell you that I replaced a temp sensor with a new one in an A-4 years ago using Teflon tape and the gauge wouldn't work. I removed it, took the tape off the threads, used plumbers pipe dope instead and it came to life. The problem, no good ground with the Teflon tape. Boy did I feel dumb! Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[rwthomas1]

Pipe dope! RT

 

[Sven]

Boy did I feel dumb!

Pipe dope!

That wasn't very nice !






-Sven

 

[Glyn Judson]

Pipe dope.

Sven, That's OK I felt like a pipe dope, I can tell you that. Remember Doug and Nancy Russell? It was on their E29 that I tried to defy the laws of conductivity. Glyn

 

[Sven]

Sven, That's OK I felt like a pipe dope, I can tell you that.

Well, the sequence of posts was just too perfect on this otherwise bad-news day (Mars Science Laboratory got slipped 2 years which is probably the biggest blow to JPL since the Challenger disaster). When I started laughing at the two posts I realized it was at your expense and I felt kind of guilty, but not really

Remember Doug and Nancy Russell? It was on their E29 that I tried to defy the laws of conductivity. Glyn

Of course ! How are they doing ? We still have pictures up on mac.com from when we were all on Dawn Treader, with Bruce the Magnificent; the Babe magnet


-Sven

 

[hodo]

Don't forget to check the length of the pencil zinc. Some will bottom out before they get tight, so you neet to trim about 1/4" off the end.
Pipe dope is what I've always used, and no problems.
Harold

 

[Rocinante33]

I think Hodo has it right. You have to cut the end off of the zinc so it can fit into the heat exchanger. Maybe you didn't cut it short enough. Mine needs about 3/8" taken off.

 

[mherrcat]

Ooops. Saw another thread on heat exchanger zincs and thought I was responding to this one!

I replaced my zinc last weekend. The zinc was completely gone; was probably never checked since the new heat exchanger was installed. There was teflon tape on the plug, but the threads were NPT so I didn't use any when I replaced. Didn't see any leaks after 20 minutes running the engine.

I did have to cut about 1/2" off to get it to fit.