This was touched on in another thread, but I didn't want to hijack, so I'll begin anew.

Here's picks of my freeze plug I had replaced about 2 weeks ago:



Notice that there's no visible outer wear when you look at it. I figured this was due to some sort of coating, possibly zinc plating as otherwise I would expect it to be green if it were copper or brass, or rusty if it were steel. I elected to let the shop replace it as it was directly behind an engine mount and I didn't wanna mess with pulling that.

Here's what it looked like on the inside:



Note the heavy corroded wear at the bottom of the plug. Basically, the plug corroded from the inside out. I know it's probably hard to see, but underneath some of that caked on antifreeze, the plug looks exactly like the outer side. It's just the bottom edge that corroded, which leads me to my question:

What are these things made out of? I'm curious because the the mechanic said it was due to electrolysis, but I'm curious as to what exactly am I "electrolysizing"? Why would I be creating an electrical current in my A/F? Do I have a bad ground somewhere? Am I going to have all my other freeze plugs blow out on me?

I'm really hoping that the plug was plated and accidentally scored upon installation and eventually failed by corrosion due to compromised plating.

 

i think its zinc plated steel. with crappy/missing/thin plating in those 2 sections. the plugs probably sat around and started rusting before they were plated, then the plating didn't take. i don't buy into the electrolysis.

edit - will the other plugs rust out ? maybe. on the day your engine was built, a guy had a big box of freeze plugs that he pulled parts from. that box came from a big batch that was stamped and then plated. odds are that if one has thin or missing plating, then a lot of them in the batch are that way, and the odds are that you more than one in the box was bad, and more than one in your engine is bad. sorry for the doom and gloom. i wouldn't do anything about it, just wait and see. your picture looks perfect from the outside.

 

the zinc coating only protects for a limited time

'conventional' anti-freeze has a silicate coating that is supposed to block corrosion and I believe that is the 'goo' that still covers most of the freeze plug

as you can see,
the silicate layer is not perfect
and flakes off some metal surfaces

brass freeze plugs are installed by many high performance engine builders routinely, and bronze is even better

if you are interested in the subject of internal engine corrosion (and cooling)
you might enjoy reading the propaganda about 'non-aqueous' coolant formulas and their advantages over at
Evanscooling.com

further interesting reading can be had by doing a google search something along the lines of:

'cylinder liner looks like it has been eaten by termites'

the stamped steel water pump impellor on Magnum 5.2/5.9 V8 engines
are also prone to this 'cavitation-corrosion' style failure

it may sound very strange
but harnessing the vast power of cavitation
might someday be the secret
to Nuclear Fusion electric power generation plants

 

I have had this happen to me before on other engines, especially if they sit dormant for long periods. You may not believe it, but your cooling system does generate a small voltage. Try putting your multi-meter probe into your radiator coolant and measure on millivolts and see what you get. I've heard people reading up to 1 volt. I don't know what causes this exactly, but my guess is all the dissimiliar metals + stray currents in the electrical system.

See: http://www.awrracing.com/media/electrolysis.pdf

 

I insisted that the engine shop use only brass core plugs when they were redoing my engine.

 

Some race shops thread the block and use pipe plugs.

 

Thanks for the info guys. I had no intention of having all the plugs pulled and swapped. especially since a few look as thought the tranny would need to be pulled. Perhaps if I ever have it pulled I might do it as preventative maintenence.

 

How much did the shop charge you to replace it, I have one that's starting to leak

 

$167 due to the location behind the engine mount. The shop charge was 0.6 hrs labor on the plug itself.

 

jeez, mine got a hole right in the middle of it.

what do you think about the rubber plugs you see? temporary only?


I put in a rubber one, so i could get home... i should prolly replace it