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Posted by D Sherman [72.47.153.24] on Sunday, February 12, 2012 at 14:29:15 :
In Reply to: Re: Replaceable zinc plugs posted by Kaegi [24.16.253.154] on Sunday, February 12, 2012 at 12:54:25 :
Mine have 1/2" pipe threads, which means about a 3/4" hole -- too big for the petcock hole. That's the size hole for the temperatures sender on the military engines, but not civilian. Plus, you still need the temperature gauge and petcock. The only place I can think to put one in would be the heater hose outlet in the block if you didn't have a heater, or put it in with a tee.
As a practical matter, though, I think it's unnecessary. All this talk about electrochemistry is moot if modern anti-freeze is used. Also as a practical matter, I don't think the old-time engineers worried about it too much. We see cast iron fittings soldered onto brass radiators, brass thermostats set into cast iron housings, and brass petcocks and temperatures senders screwed into cast iron blocks. They never cause corrosion problems.
Sometimes a little knowledge is a dangerous thing, and in this case some people are obsessing too much about a theoretical problem that isn't a practical problem. I suspect my zinc anode plugs were intended for marine engines or some sort of cooling system that uses fresh untreated outside water.
Bear in mind also that if you have an environment where electrolytic corrosion is an issue, you don't want to use brass at all, not even without any iron in the system. Brass is a mixture of copper and zinc, and in a corrosive environment, the zinc will dissolve and leave a porous, crumbly matrix of copper. I've seen it happen. The "marine bronze" alloys don't contain any zinc for that reason. Also, if we want to over-ana.lyze it, in a radiator you have tin/lead solder, so there are actually 4 metals in perfect electrical contact and exposed to the coolant all the time. Tin, lead, and copper are all less reactive than iron and zinc, and of course the lead is the least reactive of all. If plain water used as the coolant for a long time, eventually all of the brass gets thinner and thinner until it starts leaking in too many places to solder up.
The bottom line is that it's plain water, not any particular metal, that wrecks a cooling system. With proper coolant, all the metals are safe. Without it, there will be problems in lots of places, not just the water distribution tube.