Thor Forums

[FW28z]

They use a non-metalic plug to protect the tank.

As fhenn indicated - anytime two dissimilar metals are in contact with each other in the presence of water, galvanic current occurs.

I am going to fall back my previous experience with boats on this. Boaters have to contend with serious galvanic corrosion issues, so I picked up a bit of "horse-sense" along the way when I had boats.

Galvanic current will corrode the less noble metal. Aluminum is less noble than brass, so if you use a brass plug, the tank will be more prone to corrosion. The amount of corrosion depends on the two metals, the distance they are apart on the Nobility Scale, their surface area, the conductivity of water (due to dissolved mineral content), and so on.

If you want to replace the plug with a metal one, then you should replace it with an aluminum plug, or with one having a sacrificial anode. Even if the aluminum plug may be a different alloy, it's position on the Nobility Scale vs. the tank's aluminum should not be significant, and thus will not likely cause significant corrosion.

I know some will say that Atwood heaters do not require anodes, but the heater has a brass overpressure valve, and assuming that is in contact with the aluminum tank, then some corrosion is occurring anyway. The corrosion rate will not likely be high because the surface area of the tank is much larger than the brass valve, but it will occur over the lifetime of the tank.

This topic is piquing my curiosity - I should measure between the overpressure valve and tank with an ohmmeter when I get my rig out of the snow bank and see if there is any continuity.

Atwood may not use an anode as they may feel the rate of corrosion due to the overpressure valve may not be significant. Or if there is electrical isolation between the overpressure valve and tank, corrosion will not likely occur; which is why I want to measure between the valve and tank with an ohmmeter. I want to see if there is any metal-to-metal contact.

But adding a brass plug increases the ratio of the brass to aluminum surface area, and if combined with the overpressure valve, perhaps to the point of having an issue.

Camco makes plugs for Atwood heaters that have magnesium anodes having 1/2NPT threads. If you buy one, make sure it is for an Atwood tank, as Suburban tanks I believe use 3/4NPT threads. Magnesium and zinc are less Noble than aluminum, so they will protect the tank (boat anodes are usually zinc or magnesium).

However, when using such anodes, a small amount of dissolved metal will be introduced into the water system since the dissolving anode will release metal into the water. Whether or not this increases the metallic content more than the typical dissolved metals already in the water I do not know.

So, I would recommend staying with the nylon plug and not worry about the small rate of corrosion that may occur in the tank due to the brass overpressure valve. But if you want to replace the plug with a metal one, use an aluminum one, with or without an anode (the Camco anode plugs for Atwood tanks are aluminum).

I would avoid using a brass plug.

Sorry for the long post...