BB767

After scanning the archives I didn't see an answer. So here is a question about replacing the factory aluminum drain plug...



...seen here in AIM, UPC 11-13, page A4.



The aluminum drain plug is on the right and it's in such an unhandy spot for a wrench, I wondered if I could use a brass petcock in the aluminum radiator. I've heard the problem with not using the factory aluminum plug is anything not aluminum would lead to dissimilar metal corrosion with the radiator. If there's even a remote chance I'd damage the radiator I'll stick with the aluminum drain plug.

Thanks everyone.

Thomas

rongold

I have a brass petcock in my DeWitts aluminum radiator for the last 8 years--NO PROBLEM !!! The way I understand it, you only get galvanic corrosion if electrical current passes through the joint--as in the case of a spark plug.

JohnZ

If you're really concerned about it, Tom DeWitt has aluminum drain ***** - I have several of them.

BB767

Thanks John, I was hoping you'd see this and have an answer. I really am concerned so you've provided the perfect solution. I was unaware such a item existed. I'll contact Tom at DeWitts and pick up a couple. Many thanks.

Thomas

Powershift

My 1967 car has a brass drain petcock in the original Harrison aluminum radiator for over 22 years…………no problem yet.

The aluminum petcock will likely strip out on you after 1-2 uses………but that is your choice.

Larry

ejboyd5

Unfortunately not so! Galvanic corrosion occurs when dissimilar metals having different electrode potentials exist together in the presence of an electrolyte. Depending upon the relative potentials of the metals involved, one metal will become an anode and the other a cathode. The electolyte (in this case the coolant) facilitates an ion transfer between the metals resulting in erosion of the anodal metal with a concurrent deposit on the cathodic metal. No exterior source of "electricity" is necessary for this transfer to occur. The speed of the ion transfer (erosion) is dependent upon the difference in electrode potential between the two metals, i.e., the greater the difference, the faster the transfer. In the instant case, use of an insulating medium such as Tef-Gel or Tuff-Gel should allow many years of peaceful coexistence between a brass valve and an aluminum radiator.

Frankie the Fink

Absolutely correct; most boat parts places offer "sacrificial anode" kits because the dissimilar metals on boats degrade over time (galvanic response) and there is no electrical connections to those either. My boat is always in fresh water and I still have to replace them regularly!

BB767

My Dad's sailboat was in saltwater and we were always extremely mindful of dissimilar metal corrosion. That's why I brought this up to begin with just to be on the safe side. You can see where someone in the past had already rounded the head of the plug. The plug is aluminum so it's soft to begin with and it really is in an awkward spot which doesn't help matters. I thought a petcock would be handier.

Thanks again everyone for your posts. The Corvette brotherhood is the best.

Thomas

BB767

Here's a follow up to my question about dissimilar metal corrosion using a brass radiator drain valve in an aluminum radiator.
I contacted DeWitts about purchasing one of their aluminum drain valves and explained why I wanted it.

They told me that all their new aluminum radiators come equipped with brass drain valves.
They said using a brass drain valve in an aluminum radiator should not present a problem what-so-ever with dissimilar metal corrosion.
They only produce and sell aluminum drain valves for authenticity purposes only.
For durability reasons they said "a brass drain valve is the preferred type to use in a Corvette radiator".

So that should answer that question definitively. Thank you everyone for your help with this.

Thomas

Frankie the Fink

Sort of. Nearly every other metal is "noble" compared to aluminum (not by much for brass though) so the potential is there for galvanic corrosion; However, It will prob be fine for many, many years... Especially in the absence of an electrolytic (like salt water or mineral-laden fresh water).

Powershift

Frankie:

I understand galvanic corrosion. However, just remember that the auto cooling system is (or should be) protected by a high quality coolant that has additives that MINIMIZE/PREVENT COOLING SYSTEM CORROSION BY DESIGN.

Our older autos have brass, aluminum, lead solder, steel, cast iron, copper, etc all co-existing or in contact with one another either thru direct bolting or thru the the coolant itself. Quality coolants (like Zerex G-05) will minimize or prevent galvanic corrosion when properly used.

Awhile back, I used a Fluke multimeter in my 1967 car's cooling system with G-05 to measure this galvanic potential. With super clean electrodes, the current flow was about 150 mv, but it went down to near zero with time. Cleaned the electrodes and the number went higher, and then decayed back to near zero with time.

Tom DeWitt confirmed what I stated earlier back in Post #5.

Larry

Frankie the Fink

I think we are in agreement....