What is electrolysis?

[Pecky]

Hi guys,

One of the our club members over here had a neighbor with a WRX which had cooling problems and he ended up replacing two radiators in 8 months. The reply below was from the local road assistance organization and I thought you may find it interesting.




WHAT IS ELECTROLYSIS?
Electrolysis is the result of either a chemical reaction and / or electricity flowing through your cooling system and causing an electrochemical charge across the aluminium. This results in rapid corrosion and severe damage to the components in your cooling system including discoloration, pitting, flaking, and pinholes. Most common in late model vehicles, hot rods and street rods, electrolysis will usually occur if there is a defective or missing ground on one of the numerous potential electrical sources.

HOW CAN I TEST FOR ELECTROLYSIS?
To test if your cooling system has been affected by electrolysis, you will need to test the voltage in your cooling system. The first step is to connect the negative lead of a volt/ohm meter to the battery ground. Then, carefully insert the positive lead of the volt/ohm meter into the coolant inside the radiator without contacting the filler neck. If the result is more than 0.10 V, this indicates that there is an electrical current flowing through the system. Continue to check the voltage between the coolant and (1) the engine (2) the frame by touching the negative lead to each respectively. Repeat test with the positive lead touching the radiator instead of the coolant.
A simple and usually effective way to try and determine the faulty electrical source is to conduct this test with the engine running and all vehicle accessories on. Have a friend or co-worker systematically switch on and off components of the car as you monitor the meter (in some instances, fuses need to be removed in order to switch the accessory off. You may also want to test with the ignition off). If voltage drops when disconnecting an electrical circuit, that circuit represents a likely electrical source.

WAYS TO PREVENT ELECTROLYSIS:

Unfortunately, only the careful monitoring and proper maintenance of your cooling and electrical system can really prevent electrolysis from destroying your system. ALWAYS make sure the radiator is not used as a ground and that all components are functioning properly. Periodically test your system and check for any discoloration or pinholes – especially around the tube-to-header joints and tubes near the centre of the core by the electric fan mounts.

 

[Kevin]

Yes, that is interesting.

Older Range Rovers that travelled regularly at highway speeds used to have similar problems with water pump failure (also aluminium engines). If I recall correctly, it was because the impeller was not aluminium. The solution was to swap in a larger pulley to slow to pump down and hence decrease the electrolysis effect.

 

[jonbob]

The rangie problem was caused by dissimilar metals in the pump and a high tip speed that caused removal of the protective coating from the corrosion inhibitor. This produced a galvanic cell between the impeller and the rest of the system. The aluminium acted as a sacrificial anode, protecting a cast iron impeller where the corrosion inhibitor was ineffective.

The problem that David is talking about is the cooling system acting as a ground return, essentially transfer of electrons via the cooling system rather than the wiring, which will induce corrosion.

 

[nipper]

Also do NOT use tap water. Always use deionized water in the cooling system (or pre-mix) for this same reason.


nipper

 

[Rally]

I use genuine, and change it annually

 

[Martini]

Yes, that is interesting.

Older Range Rovers that travelled regularly at highway speeds used to have similar problems with water pump failure (also aluminium engines). If I recall correctly, it was because the impeller was not aluminium. The solution was to swap in a larger pulley to slow to pump down and hence decrease the electrolysis effect.

Unfortunately slowing the flow of coolant won't change its capacity to conduct electricity. I'm not an electrical engineer, but from what I recall electricity propagates at a speed proportional to the speed of light according to certain properties of the material through which it propagates. Electrical charge propagation speed would typically be something on the order of 60% or 95% of light speed, for instance, depending on the conductivity of the material. Therefore the net effect of slowing the coolant velocity on the order of feet per second would be negligible.

Slowing the water pump might help if it was a voltage source, and by slowing it you reduced its voltage contribution to the coolant. I'm not sure if this is plausible or not.

Jim

 

[jonbob]

Unfortunately slowing the flow of coolant won't change its capacity to conduct electricity. I'm not an electrical engineer, but from what I recall electricity propagates at a speed proportional to the speed of light according to certain properties of the material through which it propagates. Electrical charge propagation speed would typically be something on the order of 60% or 95% of light speed, for instance, depending on the conductivity of the material. Therefore the net effect of slowing the coolant velocity on the order of feet per second would be negligible.

Slowing the water pump might help if it was a voltage source, and by slowing it you reduced its voltage contribution to the coolant. I'm not sure if this is plausible or not.

Jim

The prevention of corrosion with dissimilar metals relies on developing film on the metal surface that inhibits the transfer of electrons (either an oil-based film, or the development of a stable oxide or other insoluble and stable metallic salt). If the tip speed of teh pump impeller is too high, this film is eroded away and exposes the cast iron surface to the coolant. Either the impeller will continue to corrode and erode away, or any areas of untreated aluminium will then rapidly corrode due to the production of a galvanic cell between the cast iron and aluminium.

Jon

 

[Martini]

The prevention of corrosion with dissimilar metals relies on developing film on the metal surface that inhibits the transfer of electrons (either an oil-based film, or the development of a stable oxide or other insoluble and stable metallic salt). If the tip speed of teh pump impeller is too high, this film is eroded away and exposes the cast iron surface to the coolant. Either the impeller will continue to corrode and erode away, or any areas of untreated aluminium will then rapidly corrode due to the production of a galvanic cell between the cast iron and aluminium.

Jon

Thanks for the explanation, it at least appears to make sense! I'm a mechanical guy, not so much a chemical guy. Is this something that occurs with any regularity with our cars? Seems like an aluminum or durable synthetic impeller would have made sense in this case. Obviously this would be costlier to produce and durability would be a primary concern, but it would prevent bimetallic corrosion or the need for a protective coating on the impeller.

Interesting situation nonetheless.

Jim