Heat exchanger advice please

[Brisyboy]

Just had a look at the pencil zinc in the main heat exchanger (Lehman 135) and the nut came out but the zinc stayed in. I took off the end cap and removed it by tapping it into the exchanger. There was plenty of meat left on it (crusted though)

So.......my question, even if the zinc breaks off, but remains firmly in the threaded hole, is it still doing its job.

Supplementary question- do the smaller oil and transmission coolers need their own zincs? I have to replace one of each and there is the option.

Thanks

 

[Insequent]

For a zinc to actually work there does need to be good conductivity to the block or HX. Just sitting in the hole won't do it, and the crust is oxide & hydroxide rather than metal, which is another factor stopping it working properly.

My oil coolers have zincs at each end of them. I would take the option of getting one with zincs. The purpose of the zinc is to stop corrosion of the cooler and it tubes, and zincs are cheap. Particularly as we have a local manufacturer in SE Qld.
https://www.cathodicanodes.com.au/

I get the crusty stuff on my anodes as well. In my case I think it comes from river water at my marina being less salty than the ocean. I've decided to replace them more often, as I've had some break off as well even though only 'half worn'.

 

[kchace]

A normal heat exchanger zinc on a 135 has a brass base with the zinc pencil screwed into it. If the zinc breaks off, it usually breaks off at the base, so you’d only have a tiny stub of zinc left in the base to do anything. As stated above, a zinc needs a good electrical contact with the item it is supposed to be protecting. So the broken off piece isn’t going to do anything.

Oil coolers on the Lehman 135s don’t normally have zincs.

Ken

 

[rgano]

I have taken to pulling and examining my five engine aluminum anodes (Yanmar 315 HP) every 90 days because, just like the twin FL 120s I owned before, the swollen anodes (zinc or AL) make it nearly impossible to remove them later on without snapping them off. BTW, dumping the anode holders into a small jar with 4-5 ounces of muriatic acid cleans the old anode right out of them. I have had the same holders for years.

 

[Alaskan Sea-Duction]

So when replacing the zincs do you wrap the threads with teflon tape?

 

[rgano]

So when replacing the zincs do you wrap the threads with teflon tape?

I once put some sealant on the threads to see if maybe that would prevent corrosion of the threads to prevent them snapping off, but I don't know that it really did much good. I do not think teflon tape would help. Who cares when you got muriatic acid handy?

 

[Alaskan Sea-Duction]

I was thinking of a grounding issues, making sure the zinc is properly grounded.

 

[Comodave]

I don’t put anything on my anodes when I install them. Never had any issues with leaks.

 

[firehoser75]

Tom,
According to Tony Athens, using a thread sealant will not impede the conductivity. This has been tested using a multimeter by Seaboard employees. They recommend Rector Seal 5 (which is yellow in colour).
As Comodave says, many have never used a sealant and not experienced leaking issues. Personally, I now use the Rector seal and find it easier to remove the anode when changing, however, it does require a bit of cleanup before reinstall so .......

 

[Tator]

My trick is to untighten the brass end until loose of the cooler but still attached to the anode. Then wiggle the end while still attached to the anode in circular motions to loosen the anode. Has always come out.

Tator

 

[bayview]

The plug threads are designed to distort and seal when tightened. Reusing them reduces this effectiveness.

I always used rector seal but measured conductivity to be sure. always showed good conduction.

Threaded rod connectors fit some zincs and can be screwed onto eh stuck zinc after the plug comes out. Some wiggling and the zinc comes out.

 

[Brisyboy]

A normal heat exchanger zinc on a 135 has a brass base with the zinc pencil screwed into it. If the zinc breaks off, it usually breaks off at the base, so you’d only have a tiny stub of zinc left in the base to do anything. As stated above, a zinc needs a good electrical contact with the item it is supposed to be protecting. So the broken off piece isn’t going to do anything.

Oil coolers on the Lehman 135s don’t normally have zincs.

Ken

Thanks Ken,

So..... your post has made me realise I don`t completely understand what a zinc is meant to be doing. Is it meant to be protecting the whole cooling system or just the cooler it sits in. I understand that the anode must have a good connection to the cooler, but does the cooler need to have a good connection to the engine and the rest of the boats grounding network?

It also begs the question that the main heat exchanger has a large anode (to protect itself or the rest of the engine), therefore why doesn`t the tranny and engine oil coolers have one?

 

[rgano]

Some engines, like my Yanmar have an anode in each cooler; fuel cooler, intercooler, oil cooler, tranny fluid cooler, and heat exchanger. My Lehmans came to me with ports in the three coolers they employ; oil cooler, tranny, and heat exchanger. Later I bought cupro-nickel oil and tranny coolers which did not have the anode ports. One time I found an engine drip pan overflowing with seawater because the BRASS plug in the anode port had rotted out. As to the continuity between anode cap and cooler, if you put teflon tape on the threads, I think a continuity test with a VOM will show the threads cut through the tape enough to give good contact. I also found that my on my FL 120s the coolers were cushioned in their metal hangers with rubber inserts eliminating their electrical contact with the engine; so I added ground wires from the coolers to the engine.

 

[KnotYet]

Thanks Ken,

So..... your post has made me realise I don`t completely understand what a zinc is meant to be doing. Is it meant to be protecting the whole cooling system or just the cooler it sits in. I understand that the anode must have a good connection to the cooler, but does the cooler need to have a good connection to the engine and the rest of the boats grounding network?

It also begs the question that the main heat exchanger has a large anode (to protect itself or the rest of the engine), therefore why doesn`t the tranny and engine oil coolers have one?

A zinc will only protect the metals that form part of the circuit it is a part of.
I would want to have separate zincs for any separate metal parts that don't connect.
Also, the further away a zinc is from a metal part the less protection it will provide.
I think those coolers should have zincs of their own unless they are made of special alloy.
I have seen some that do.

 

[SoWhat]

My lehman transmission and oil coolers have drains, no anodes. Unfortunately the first warning you get of corrosion is a transmission full of water. Not aware of any solution.

 

[rgano]

My lehman transmission and oil coolers have drains, no anodes. Unfortunately the first warning you get of corrosion is a transmission full of water. Not aware of any solution.

Changing the coolers every five years will probably obviate that issue.

 

[rslifkin]

My lehman transmission and oil coolers have drains, no anodes. Unfortunately the first warning you get of corrosion is a transmission full of water. Not aware of any solution.

Depends on the transmissions and how much pressure the cooler loop is under. On most setups I've seen, the indicator of failure is trans fluid out the exhaust after startup.

 

[Codger2]

Some engines, like my Yanmar have an anode in each cooler; fuel cooler, intercooler, oil cooler, tranny fluid cooler, and heat exchanger.... As to the continuity between anode cap and cooler, if you put teflon tape on the threads, I think a continuity test with a VOM will show the threads cut through the tape enough to give good contact.

My experience with my Yanmars has been exactly as described above.

 

[SteveK]

anyone use anti seize, dielectric grease or even just a grease.

 

[catalinajack]

I believe that swollen anodes in the heat exchangers is a common problem in Lehmans, probably other engines as well. I got tired of having to remove the end cap and cleaning the bits out. The diameter of the standard anode is 1/2 inch. I switched to 3/8-inch anodes. They, of course, don't last as long but no more having to punch out broken off anodes.

 

[kchace]

A zinc will only protect the metals that form part of the circuit it is a part of.
I would want to have separate zincs for any separate metal parts that don't connect.
Also, the further away a zinc is from a metal part the less protection it will provide.
I think those coolers should have zincs of their own unless they are made of special alloy.
I have seen some that do.

Zincs or any sacrificial anode is only needed to protect dissimilar metals. If a cooler is made from all the same metal or metals that are very close to each other on the galvanic scale then any corrosion is very slow. The higher quality oil coolers are this way so no zinc is needed and they last more than 10 years.

Ken

 

[Brisyboy]

Zincs or any sacrificial anode is only needed to protect dissimilar metals. If a cooler is made from all the same metal or metals that are very close to each other on the galvanic scale then any corrosion is very slow. The higher quality oil coolers are this way so no zinc is needed and they last more than 10 years.

Ken

Ken,

You make a point re the dissimilar metals and I assume the outer case and inner tubes are the same - no problems - where does the solder holding the end caps on etc fit in the equation - could this be a justification for an anode?

 

[KnotYet]

Zincs or any sacrificial anode is only needed to protect dissimilar metals. If a cooler is made from all the same metal or metals that are very close to each other on the galvanic scale then any corrosion is very slow. The higher quality oil coolers are this way so no zinc is needed and they last more than 10 years.
Ken

Unfortunately, you will seldom find any pure, unalloyed metal in your boat nowadays.
Zincs can also protect against stray current electrolysis as in a zinc on a bronze prop.

 

[Tator]

One other tip. I always use a plumber's pipe brush to clean the threads and hole in the exchanger when changing zincs. It gets rid of any the crud that builds up and helps prevent the zinc from getting stuck. A useful tool to have in ones arsenal.

Tator

 

[kchace]

Ken,

You make a point re the dissimilar metals and I assume the outer case and inner tubes are the same - no problems - where does the solder holding the end caps on etc fit in the equation - could this be a justification for an anode?

I’m sure it could but don’t overthink it. Some heat exchangers especially the small oil coolers don’t have space for a zinc and
last many years.

Ken

 

[Brooksie]

Am I mistaken or could someone take a piece of oversize zinc rod, turn 2-3" of it down so it just slips through the pipe thread opening, slide a pipe die up that portion and cut the pipe thread, slide it off and grind a hex or cut a slot on the remainder; thus making a one piece zinc?

 

[bayview]

I believe that swollen anodes in the heat exchangers is a common problem in Lehmans, probably other engines as well. I got tired of having to remove the end cap and cleaning the bits out. The diameter of the standard anode is 1/2 inch. I switched to 3/8-inch anodes. They, of course, don't last as long but no more having to punch out broken off anodes.

threaded rod couplers will fit 1/2" zincs

 

[sunchaser]

Several OEM Cupro nickel heat exchangers are designed and metallurgy speced for no zincs. All Perkins Sabres and Cat 3054/3056 come to mind. I've heard there are others, just not laid eyes on them.

 

[rgano]

Am I mistaken or could someone take a piece of oversize zinc rod, turn 2-3" of it down so it just slips through the pipe thread opening, slide a pipe die up that portion and cut the pipe thread, slide it off and grind a hex or cut a slot on the remainder; thus making a one piece zinc?

You might well end up with a crumbled zinc which would not be removable.

 

[Mike Negley]

Dialelctric grease is an insulator. It is printed on the tube. If you use it test with an Ohm meter.