The following is from a dealer newsletter written by Jay Ross, the owner of Applied Chemical Specialties, the manufacturer of No Rosion/Hyperkuhl cooling products which contained interesting information regarding electrolysis that you may interest you:
There are two types of electrolysis that generally occurs in automotive cooling systems:
1) Galvanic Action: Electrolysis between dissimilar metals, in which coolant acts as an electrolyte. This is usually less than 0.3 volt (300 mV)
2) Stray Current: Electrolysis from an improperly grounded under hood electrical component or shorted wire. This is almost greater than 0.3 volt (300mV)
With galvanic action, coolant acts as an electrolyte that is in contact with the different metals in a cooling system - iron, aluminum, copper. brass, etc. Each metal has a unique "electornegativity" which is a measure of it's ability to attract electrons. Metals with higher electronegativies strip electrons from neighboring metals with lower electronegativies, producing a small electrical current that is transferred via the coolant. Stripping of electrons from the surfaces of metals with lower electronegativity (i.e. aluminum) causes damage that over time becomes deep enough to to result in a leak. Depending on the metal's thickness, it can take months or years before enough damage occurs to produce a leak. But sooner or later, it will happen.
Stray current is much more immediately destructive. It is caused by electrical components that conduct well over 300 mV through the cooling system - the source of which is usually a faulty ground or shorted wire. The damage it causes takes place over a much shorter period in some cases only weeks!
Is it possible to identify which type is taking place in your cooling system? YES! Using a volt ohm meter, connect the black (ground) lead to the battery ground and lower the red (positive) lead into the coolant. A reading over 300 mV indicates stray current, whereas less than 300 mV is galvanic action. If you have a reading close to 300 mV, take readings both with and without the engine running. If the reading increases when you start the engine, it is stray current. If it is unaffected by starting the engine, it is galvanic action.
How can you prevent electrolysis? With stray current, you need to identify the source and eliminate it. Sometimes that's easier said than done. But usually some sleuthing will produce the culprit. With galvanic action, it's simple, just use No Rosion as directed. The molybdate ingredient in our product forms molecular thick surface films that prevent the transfer of electrons from cooling system metals yet are thin enough to have no negative effects on heat transfer.
Sometimes you can even see it working. How? We've had customers report a drop in readings on their voltmeter after adding No-Rosion to their cooling system. It's not always reproduceable and varies based on a number of factors to include system metallurgy. But is does and has happened in some systems.
What is a sacrificial anode and does it help? It is a metal of low electronegativity, usually zinc that is inserted into a cooling system so it can sacrificially contribute to electrons in order to protect other metals of relatively low electronegativity. And yes, it does work. But the problem is that the protection it provides is very localized. Usually within only 6 - 8" of the anode so it won't provide protection to the entire system, as does No-Rosion.
A friend of mine who is a machinist told me that a zinc anode in a cooling system does very little to prevent electrolysis as it is effective for salt water applications. A magnesium anode is more appropriate for a fresh water cooling system.
Original Post