Tech Tips - Electrolysis/Stray Current and Chemical Corrosion

Tech Tips - Electrolysis/Stray Current and Chemical Corrosion
The need to test for any stray currents in the cooling system is imperative.  Stray currents can cause premature corrosion failures in radiators, water pumps and thermostat housings as well as premature ageing in coolant hoses.  When we say premature, we mean in as little as three months.
NRMA Motoring & Services did a repair on a vehicle which the radiator was replaced, three months after the owner took delivery it was found that the new radiator was so badly corroded it was irreparable. We examined the dismantled radiator core and found evidence of electrolysis and mixed coolants.
Do's and Don'ts
There are a number of do's and don'ts when changing a vehicles coolant.

  • Never mix different brands of coolants or inhibitors.  A mixture of incompatible coolants can induce radiator fouling and can reduce the corrosion protection of the coolant. Always flush out the old coolant.
  • Never use coolants that foam as this will lead to increased cavitation erosion of the water pump.  Shake the bottle of coolant then let it stand for 5 seconds, if the foam has broken and the fluid has returned to normal then it probably wont foam in the cooling system.
    If the foam has not broken after 5 seconds then it might pay to find another product.
  • Never undertreat a cooling system as the incorrect ratio of coolant can actually increase the corrosion rate to above that of plain water.
  • Only use the best quality water.  De-mineralised is the best, never use bore or spring water.
  • Always check for stray electrical current in the cooling system.
  • If the vehicle is within the new vehicle warranty period, always use the manufacturer's recommended coolant as to do otherwise could void the warranty should the cooling system fail.
  • Always use the service stickers supplied by the coolant manufacturer to avoid any confusion as to which type of coolant is in the system when a top up is required.
  • Always dispose of used coolants correctly.  All used coolants will contain heavy metals irrespective of their claims of being environmentally friendly.

Whilst not wanting to pick on any one are of the automotive industry, our own experience tells us that many vehicle we have examined for electrolysis and chemical corrosion damage are those that have had recent paint and panel repairs.  If you suspect that a radiator has failed from electrolysis and you can't find any apparent reason for it, look for signs of recent repairs (keep in mind that the problems can exist right from the time the vehicle was manufactured).

If you spot repairs, be wary of earth wires that:

  1. Are not connected.
  2. Are loose, corroded or insecure.
  3. Earth wire mounting points have recently been painted, thus paint may be down the threaded holes causing poor earth contact.
  4. Whilst you are monitoring the presence of stray voltage in the cooling system, have a fellow worker operate the brake lights, parking, head and high beam lights and check for any increase in voltage readings in your multimeter.
  5. Also, turn on as many accessories as you can to load the vehicle's electrical system whilst monitoring stray current.
  6. Check battery cables and mid cable securing points for corrosion and tightness.

 Additional Information:

In recent times we are coming across more and more cooling systems and engine failures associated with chemical corrosion.  It is a problem common with poor quality inhibitors, low dosages of inhibitor, but we see many where different brands of inhibitors have been mixed and the results are catastrophic.

The mixing of different brands can degenerate into the formation of a chemical cocktail, which can strip metal away with amazing speed.

The internals will show a dark grey or black discolouration.  You can also try removing the radiator cap and feeling the top of the core tubes, they will feel flexible, even soft to touch.  Where this indication is present you many also find items such as thermostat
housings and water pumps showing signs of cavitation.

Where chemical corrosion has occurred, quite often the cooling systems components such as the thermostat housing, water pump, heater and coolant pipes will be badly discoloured.

Chemical corrosion can also lead to the formation of small hard deposits of metals and rust within the radiator or engine block causing hard to find overheating problems.  These deposits can be very hard to shift if they have been building up over a period of time as such, become firmly lodged in coolant tubes and within water passages etc... Keep in mind that 1.6mm of corrosion build up on aluminium causes as much heat retardation as 104mm of cast iron!

In the event where you have come across cars effected by chemical corrosion, you would be best advised to use a good flush to move any hardened deposits that have lodged in out of sight areas.

Chemical corrosion can affect the hard to see areas of the cooling system, so as we mentioned earlier, where any doubts exists or if you don't know the vehicle, flush the coolant and replace it.

Mixing of coolants and even poor quality coolants, can cause foaming and its the introduction of oxygen that leads to the formation of air bubbles that create their own version of cavitation erosion.

The bubbles or vapours which result from the chemical activity, continually explode against the engine's hot spots and if not caught early can completely destroy an engine.  The exploding bubbles of air cause a hammering effect on the metal gradually eroding away that area and eventually forming a small pin hole.  Often a large piece of metal will simply disappear from within the engine.  Cavitation can be particularly harsh on cylinder liners and their seals and at different points of the cylinder head and gasket.

We can well appreciate your concerns regarding the cost of good quality or manufacturers coolants in comparison to many on the market and certainly those which can be easily purchased by your customers at the supermarkets.

We suggest that keeping a few old corroded cooling components handy to help explain to customers why you only use a good quality brand coolant.  Also don't assume that your own stocks of coolant are okay.  It doesn't hurt to check that your own bulk supply isn't starting to discolour, smell (you will certainly know its gone off), or the presence of a woolly looking bacteria floating within the coolant.  The swelling of storage containers can also mean bacterial gases escaping from the coolant.


Don't assume that fitting an earth wire directly to the radiator core is a fix all.
We did a test on an aluminium core and the lead actually increase the current.