Electrolysis in the Cooling System
Electrolysis in an automotive cooling system can be hazardous to the lifespan of metal and in particular aluminum. Unfortunately though preventable, it is often left unnoticed until it is too late and leaks have already began forming throughout the system.
Electrolysis is extremely corrosive and eats away the inside lining of aluminum parts, especially thinner parts like aluminum heater cores. It is said that a current of 0.5 or more will actually corrode a cast iron block. It takes much less current to damage an aluminum engine block and many of its components. It's more like 0.15 to 0.20 volts. Use both A/C and D/C settings for this test and check specifications. Aftermarket systems sometimes require necessary grounds and such. Be Careful and run the test.
It is caused by current passing through the coolant medium between the metal components in the cooling system. This sometimes happens after adding an aftermarket part or breaking a ground and can be fixed by replacing the ground. Either way to correct this type of electrolysis the part or connection causing the excess current must be found and repaired. Check the manufacturers manual for specifications / procedures.
The second and most common type of electrolysis is when the coolant breaks down or the ratio between the coolant and the water is predominantly water. As the coolant wears and breaks down it acts like a catalyst for electrical current. This small amount of electrical current may be flowing through the coolant corroding the different metal (especially aluminum) parts.
Over time coolant breaks down and becomes slightly acidic and must be replaced. Changing and flushing the coolant will correct this second type "B" of electrolysis. Coolant manufacturers add ingredients to their coolants. Coolants are typically either EG and made with ethylene glycol or PG "propylene glycol". Propylene glycol is considered less toxic than ethylene glycol. Different manufacturers add and recommend different amounts of silicates and chemicals designed to reduce corrosion in there vehicles system.
This does not mean that straight ethylene glycol coolant is best because the water is actually beneficial in maintaining proper engine cooling. Most manufacturers offer a pre-mix somewhere around 50/50 today.
