Indigo Heat Exchanger Anode

[Marty Levenson]

I have had the Indigo heat exchanger for a few years, and realized I need to change the anode!

When I took off the brass cap all that was there was a small wire (like a brad) and some zincy goo. Access is poor, so I could not see well what was holding the "brad" in place. I tried to unscrew what was there gripping the wire with pliers, but instead, the wire pulled straight out clean...with a fair amount of resistance.

I am concerned that the remaining anode (if any) will fall into the exchanger now that it is unsupported by the wire. Am I over worrying? I would figure that the anode was simply eroded away, but what was holding the wire in place? Seems like three paths to pursue:

1. clean out the old anode residue as well as possible in place and install a new anode.
or
2. remove the heat exchanger completely, give it a good flush and clean.
or
3. re-install the wire so it supports the remaining zinc.

Time is short before we have to be out of our dock spot!

Pencil anodes are new to me, so any advice appreciated.

[JOHN COOKSON]

I don't know much about heat exchangers or their anodes.
Maybe try a bit of never seize on the threads of the new anode?

TRUE GRIT

[ndutton]

Some anodes have a wire core to keep them from breaking off prematurely.

https://www.rotometals.com/zincs-pen...nforcing-wire/

[tac]

http://www.moyermarineforum.com/foru...8820#post98820

[Marty Levenson]

Thank you all for the useful replies. The thread that tac sent was fascinating.

Tom Stevens of Indigo saw my post and sent me some good info. Not the first time he has jumped in to help: great service. The access port on the top of the short leg of the HX should allow me to clear away the debris and install a new zinc. The instruction sheet that came with my HX states that the wire inside the anode is there to keep the partially corroded blob from falling off and causing mischief. He is sending me a couple replacement anodes. Hoping I don't have to retap.

Slightly off topic but related - I just installed the Bosch fresh water pump that Indigo sells. I was going to get a second Johnson pump as a spare but decided that for a bit more money I could get a pump that would likely last 5,000 hours and keep my perfectly good four-year-old Johnson as a spare instead. The Bosch also pushes a lot more water and doesn't need the ballast resistor. It was an easy install and works fine so far.

Great to feel the A four community always has my back!

[Marty Levenson]

Yesterday I opened that access port on the top of the HX and cleaned out zinc rubble and goo. I think the screen below the zinc kept bits from falling into the guts. FYI that cover comes off easily and the gasket and o ring are reusable.

Did a longer test at the dock: 25 minutes at 1600 RPM in gear. Was worried when I saw that though it was steady at 182, it has always been 180. I was concerned some zinc had worked its way in and might cause trouble later.

In an email today Tom Stevens of Indigo reminded me that the Bosch pump I installed a few days ago moves more coolant, so was likely setting a new equilibrium.

It is initially counter-intuitive for my brain that more circulation equals a higher equilibrium, but when I bounced it off my wife she made it sound simple. The hot engine water is in the HX for a shorter time as it is moving faster. Got it! She would have made a good scientist. I think that explains the higher temp, so I will breathe easier and not chase phantom clogs. My mistake really was making two changes to the system at once without better testing in between.

Raises a possibility for me. Have wanted to put a flow sensor on the fresh water circuit for fast troubleshooting if overheating. Somewhere I read that the sensor cuts into the flow so might be a bad idea. Now, with the higher speed pump, maybe not an issue? That's down the road as I am currently only working on the top 10% of my boat to-do list as usual.

[indigo]

Marty, if you and others on the Forum will be so kind as to indulge me, the explanation for the higher operating temperature actually goes a little like this:

Assume for the sake of discussion that the original Johnson pump provided 4 GPM of coolant flow. When the engine is under some load and the thermostat is controlling at 180F, there is 4 GPM going to the thermostat, about 2 GPM gets re-circulated, and about 2 GPM passes through the HX. Therefore 2 GPM of cool coolant comes out of the HX and mixes with the 2 GPM of hot re-circulation flow and the system is in equilibrium at 180F.
Now when you change to the higher capacity Bosch pump, the system flow jumps up so that you have about 6 GPM going to the thermostat. If the thermostat only opens to the same position as it did with the Johnson pump at 180F and thus only permits 2 GPM to go to the HX, then the re-circulation flow would increase to 4 GPM. That means that the 2 GPM of cool coolant now mixes with 4 GPM of hot re-circulation flow, the coolant entering the engine is at a higher temperature and unless the thermostat opens more to allow more flow to the HX, the temperature will not stabilize and just continue to rise.

What your tests have shown is that the new equilibrium point is about 2 degrees higher. This is really not an issue at all and the really good news is that the coolant entering the engine is now probably 5 degrees warmer (about 135F) which makes life that much better for No. 4 Cylinder.

Disclaimer: The numbers I have used in this explanation are by no means the Gospel truth but are representative of the change that occurs with the additional pumping capacity of the Bosch pump. Obviously there are different pressures at work in the system as well which can also impact the flow in the different circuits.

Tom

[Marty Levenson]

Thanks, Tom - good to know how increased flow effects the system.