Convert HEX pencil zinc to regular bonding/zinc system

[zboss]

Folks,

We go through about 1 small pencil zinc in our heat exchanger about every month. According to westerbeke, this is about the schedule you should be checking.

However, its a real pain to reach and of course it sits right above the deepest part of the bilge.

I was wondering - why not replace that pencil zinc with a bronze nut and run a binding wire from the normal hull bonding/zinc to that? Is this unadvisable? If so, why not?

[Alan Mighty]

hmm ... your pencil zinc is a sacrificial anode to protect the metal(s) of your heat exchanger, which is immersed in its own tiny ocean (that happens to be inside your engine).

A zinc anode attached outside your hull is also a sacrificial anode, protecting other metal parts (eg propeller) that are immersed in a much bigger ocean.


Your question is thought provoking. But I don't see any easy way to avoid regular change of your pencil zinc.

[RaymondR]

I use this system to make keeping anodes working without having to replace them entirely, just loosen off the gland nut, tap the anode in, and retighten the nut.

[zboss]

Originally Posted by RaymondR

I use this system to make keeping anodes working without having to replace them entirely, just loosen off the gland nut, tap the anode in, and retighten the nut.

Thanks... that definitely is not an option. I can barely reach with my fingers and tiny wrench I bent specifically in the right way to reach the anode.

The other thing I was thinking was about relocating the HEX off the engine all together and mounting it to a bulkhead. This would give significantly more room to change out the zinc.

[seasick]

Another option that you might consider is the possibility of moving your transmission's heat exchanger higher up in your engine space. This might require some initial contortions, the extension of hoses etc but I don't see why it necessarily need be mounted so low.

To answer your question more specifically, the pencil zincs need to be in close proximity to the dissimilar metals within your heat exchanger to be effective. They are diffinately placed there for a reason. I have replaced this same heat exchanger in one of my previous vessels that ran a Westerbeke and this exercise makes replacing the pencils zincs an inexpensive breeze.

[RaymondR]

I am not familiar with your engine type but if they have located the heat exchanger under the engine or gear box it is possible that they are relying on thermo syphoning to circulate the oil through the exchanger and therefor you would need to be careful of where you moved it to. However if the oil being cooled is pumped through the heat exchanger you should be able to move it to somewhere more convenient.


There are probably a couple of things you need to be careful of: the pump puts out enough pressure to handle any extra head generated by raising the exchanger, and if the exchanger can drain into the gear box is there sufficient ullaged volume to allow this without the gear box overflowing.


Both the anode immersed in cooling fluid, and the dissimilar metals in the heat exchanger, also immersed in the fluid act like a battery. It is the current flow between the dissimilar metals which cause the corrosion of one of them. When you immerse an anode the current flows through the anode corroding it rather than the metals in the heat exchanger. Consequently both anode and metals being protected must share the fluid and should be in fairly close proximity to each other.


A possible solution might be to screw an elbow into the holr where the anode fits and then a tube riser so that you screw the anode into the top of the riser, however you would need to ensure that there is a flow through of some sort so that the anode is always bathed in the coolant flow and not be in an air trap.


An alternative might be to put a T piece in the coolant inlet and relocate the anode.


Photos and a bit more detail would help.

[zboss]

Originally Posted by seasick

Another option that you might consider is the possibility of moving your transmission's heat exchanger higher up in your engine space. This might require some initial contortions, the extension of hoses etc but I don't see why it necessarily need be mounted so low.

To answer your question more specifically, the pencil zincs need to be in close proximity to the dissimilar metals within your heat exchanger to be effective. They are diffinately placed there for a reason. I have replaced this same heat exchanger in one of my previous vessels that ran a Westerbeke and this exercise makes replacing the pencils zincs an inexpensive breeze.

Hi. I was speaking about the regular boat HEX, not my trans oil HEX. Our trans oil hex must be bolted directly to the transmission because it uses heat transfer to cool.

We have been able to find a exact match lenco heat exchanger to replace the westerbeke one if we ever needed to in the future - they are much cheaper. However, the HEX doesn't even need to be an exact replacement - as long as the amount of heat that is removed is the same then actual form factor is secondary.