Electrolysis is the chemical change produced by passing an electric current through a conducting solution or a molten salt.
Cooling system of an automobile removes heat from the engine and transmission by using coolant solution that circulates in the cooling system, dissipating the heat to the environment with the help of radiator and radiator fan.
Electrolysis is an enemy to the cooling system in automobiles as it is a major cause of corrosion.
Types of corrosion in cooling system
There are broadly two types.
1. Natural corrosion
A typical example of this is rotting of the fins of radiator.
2. Electrochemical corrosion
This type has two forms
A. Galvanic corrosion
This type is due to chemical reaction between dissimilar metals. It does not require an external voltage source.
B. Corrosion due to electrolysis
This type requires a voltage source. The more conductive the coolant is, the more electrolysis that will occur. If there is an issue with the ground circuit, electrolysis will be more severe.
There are different sources of electrical charge in the cooling system.
1. Friction between coolant solution and dissimilar metal surfaces like cast iron and aluminum.
2. The engine block is used as ground causing electricity to flow through it. The coolant captures charges from the block.
3. Current flow in other engine management systems including sensors, actuators, wires and control units contribute to the cooling system becoming electrically charged.
What is electrolysis?
It is the process of using electricity to separate chemical compounds, causing oxidation-reduction chemical reaction to occur.
Types of electrolysis
1. Type-A electrolysis
This type is mostly caused by grounding problems. It is caused by faulty ground circuit causing the coolant to be used as alternate return path.
The most likely paths are metal radiator, heater core and water pump seal.
An engine that misfires will contribute to this type of electrolysis. By misfire, we mean the type that occurs when the ignition coil discharges spark to the engine block which acts as ground source. This is due to spark leakage from the coil.
If this type is not fixed quickly, it degrades coolant fast and it is also one cause of frequent heater core replacement.You can diagnose this type by adding grounds, pulling fuses and removing battery terminal.
2. Type-B electrolysis
How this type happens can be likened to how batteries work. The coolant acts as a catalyst that permits ion movement in a similar way ions migrate in batteries. Just like the lead plates in a battery, the aluminum act as the electrodes. This happens when corrosion inhibitors in the coolant wear out.
Extended use of coolants and the use of aluminum for cooling system encourages this type of electrolysis.
As coolant degrade, it becomes more acidic and this creates salts from metals and minerals in the water. This increases conductivity of the coolant which encourages Type-A electrolysis to occur.
How to determine the type of electrolysis affecting the cooling system
If electrolysis goes away when battery power is disconnected, you have a Type-A but if otherwise, you have a Type-B.
Proper test for electrolysis
Put a positive test lead of a volt meter or a multimeter set to voltage range inside the coolant in the radiator or expansion tank without allowing the lead to touch any metal part.
Put the negative lead firmly on the ground (engine block or alternator housing).
Start the car and turn off all electrical accessories like radio, AC, heater and so on.
Allow the voltage reading on the voltmeter to stabilize and begin to turn on electrical accessories.
The maximum voltage reading should be 300mV. Normal voltage reading is in the range of 50 - 70mV.
If the reading is above 300mV, flush and replace the coolant and check for other root causes of electrolysis in the cooling system.
PH test on coolant solution
As coolant ages, it begins to transform from alkaline to acidic. This causes corrosion of cooling system components.
PH test helps to know the level of acidity or alkalinity of a solution. PH ranges from 0 - 14. Any value below 7 indicates acidity and values above 7 indicates alkalinity. 7 is neutral.
Normal ethylene glycol based coolants have between 9 - 10.5 PH while long life coolants have 7.5 - 8.5 PH.
If the solution is acidic, synthetic materials for intake manifolds, thermostat housings and radiator tanks starts to damage.
If the solution is basic, aluminum and solder parts can be affected.
Effects of electrolysis on the cooling system
1. Pitting or pinholes in radiators, heater cores and aluminum manifolds.
2. Destruction of nitrate in the coolant and enabling of ammonia production that attacks copper in cooling system components.
What to do to prevent or fix cooling system electrolysis
1. Change coolant regularly.
2. Use coolant solution instead of water. See coolant solution vs plain water in a car cooling system. Also, use only distilled water to dilute contentrated coolant.
3. Reduce excess electrical load by removing extra electronics to avoid overloading the ground circuit.
4. Fix corroded, missing or loose grounds.
5. Fix a misfiring engine.
6. Use an appropriate size and not an undersized alternator.
