Hot Rods Galvanic Corrosion

A sacrifical anode is mostly used on boats. It attaches to parts of the engine and the zinc anode gets eaten away rather than the engine parts. I don't know boats, but I think you need to change them when they start to wear out. As I originally stated I have one attached to my radiator cap.

 

The ones I use are 1/4 NPT , I find a place to screw them into the cooling system or I have drilled and taped the intake to install one . They work great as designed to .

 

Nitrate free coolant will also help.

 

So, if I don't have one in my system, it eats all the aluminum parts?

 

country of origin has nothing to do with corrosion.

dis-similar metals with a conductive fluid separating them is called a "battery". seriously it's electrochemical corrosion and there are ways to check for it (measuring voltage between a probe in the rad juice and ground, etc)

iron block
brass thermostat
zinc thermo housing
aluminum radiator

here's a quickie primer: https://en.wikipedia.org/wiki/Galvanic_corrosion

when i was a kid i found a book on "electrochemistry" in the library, it had some version of this chart https://en.wikipedia.org/wiki/Galvanic_series that i used to make (mostly crappy) batteries from. METALA-electrolyte-METALB. that's what you got.

electrochemical corrosion is rarely "zero" but with some metals it's pretty low so when it take 20 years you don't notice or care. iron and brass, for example. (zinc is a component of brass). but add something more reactive -- aluminum! -- and instant problem.

you can put a "sacrificial anode" (zinc block) into the radiator tank. electrically isolate the aluminum radiator.

but yeah it's a PITA.

 

Heres an article on it...

https://www.hotrod.com/articles/keep-your-cool-preventing-radiator-eating-electrolysis/

​

 

sacrificial anode is metal you literally *sacrifice* to the corrosion mechanism. you install a piece of metal you don't care about to get eaten instead of the one you do care about.

in a boat you're fighting AN OCEAN. guess who wins. sacrifices must be made!

in a car, you have a chance of winning, though it might be hard.

being old enough to remember when we usedta (against all good advice) just dump the block and radiator contents, pour in a gallon of the cheapest coolant i could buy, then top off with a garden hose, it took some time to get over the fact that that's just bad practice.

i now flush etc with the hose but do a block (pipe plug) and radiator complete drain, re-fill with DISTILLED water from the drug store, run that a bit, drain and refill AGAIN with DISTILLED water. when i ran antifreeze i buy what i used to sneer at -- pre-mixed/pre-diluted high quality coolant. the deionized water really matters.

the perfectly ordinary minerals in tap water make a great corrosive electrolyte, especially when you heat it up.

 

Galvanic corrosion or dissimilar metal corrosion does not necessarily need an electrical current to causebthrbcorrosion. There is an anodic/cathodic chart to help decide which metals are compatible. The further away from each other on the chart, the more likely corrosion will start. Case in point, titanium is very high on the anodic scale it can be destroyed literally by drawing or marking on it with a simple pencil. The carbon in the pencil will attack the titanium and eventually eat right through it. We would inspect aircraft skin for damage and use a pencil to mark the areas that needed repair. When we moved to titanium, we wrenches no longer allowed pencils on the aircraft because of the instant and serious damages carbon would do. Likewise carbon fiber compositesnare never installed where they can contact titanium. All metals are listed on that chart and will react by eating or being eaten by another metal if not properly matched. Ad electrical current and the process speeds up. I taught corrosion control for several years in the military and with some of the aircraft manufacturers I worked for. Teaching it was sometimes as exciting as watching paint dry but at the same vitally important. W lost a couple of B-52s and two crews because of corrosion, tropical humidity, and stress in July of 1969. Agterbthat, we all took corrosion control much more seriously. So closely match anodic/cathodic properties, limit exposure to electrical current flow and humidity. It may not eliminate galvanic corrosion but it will give the metals you are using a much longer life.

 

This will explain it in detail: https://performancemetals.com/pages/sacrificial-anodes-faqs How to test for it.

 

Galvanic anode.

I use a quality anti-freeze mix and contemplating using a pencil sacrificial anode in bottom of radiator. A quality thermostat housing makes a difference as well. My DD suffered from stray current causing the plastic/alloy radiator to corrode.

 

Check your radiator for small voltage. Earth leakage to the cooling system is usually the cause of your problem. Your t-housing is acting as a sacrificial anode. Also regular coolant changing will help. 3-5 years tops regardless of what the manufacturer says IMO.
Cheers Mark.


Sent from my iPhone using The H.A.M.B. mobile app

 

Electrolysis is what I have always understood it to be.
When designing houses we were always aware of using dissimilar metals from roofing material to guttering/spouting, downpipes etc, - no electrical current involved.
tomic, in post 35 gives the best description as I was taught.

 

Thanks for all the links guys. I'm all ears! I did read (or watch) everyone you gave me and I'm more confused now than before. I didn't know you had to have a masters degree in electro-chemical engineering just to add coolant to your radiator!

No, on a more serious note, this has been a re-occurring problem with this car and I really don't know how to fix it. So I just keep replacing parts and have fun driving it.

I have your typical iron block (SBC) with aluminum heads, aluminum intake, hi-flow aluminum water pump, aluminum radiator and a brass heater core, in a glass car with grounds everywhere.

I end up changing the coolant every 2-3 years, because I've lost 2 or 3 chrome aluminum (or pot metal) thermostat housings. I even had a thermostat rust through one time, to where it wouldn't heat up. I use a mechanical temp unit.

I think I'm doing all the right things, but I am a little concerned about the heads and intake though.
I use distilled water (which is highly acidic, by the way), in a 50-50 mix of antifreeze (which makes it run 5* hotter than plain tap water) and I've come to the conclusion, WE'RE ALL GONNA DIE!