Stray current

modern radiators are vulnerable to stray current corrosion because many of them are attached to the
vehicle by their plastic tanks, or are insulated from the vehicle chassis by rubber mounts.
In many cases electrical cooling fans are mounted directly to the radiator frame. Fans and fan motors
cause lots of noise, vibration and harshness so they are insulated from the vehicle on rubber mountings.
Introduce some bad electrical contacts for the fan wiring and you have set the scene for rapid electrolysis
via the cooling fans.
The same fan is probably cycling more often because it can’t rotate quickly enough as it has a bad earth
contact. These are perfect conditions for disaster – lots of stray current, longer fan ON time and a hotter
engine. A copper/brass radiator will suffer stray current damage, too. However, an old copper/brass
radiator is usually bolted directly to the vehicle body work, providing an easy path to earth for any stray
current that finds its way into the cooling system.
Plastic tanks and rubber mounts deny any stray current an easy path to ground. The environment for
electrolysis in its most virulent form now exists.
Cooling fans are by no means the only cause of stray current problems. Stray current problems commonly occur following body repairs. The cause is over-spray. Paint
does not conduct electricity. Therefore, over-spray at an earth point forces the current to find an
alternative path to earth – the cooling system.
Corrosion damage in the areas of a radiator, while operating within a squeaky-clean cooling system, is
a pretty good indication of stray current damage.
In simple terms, stray current is a chemical/electrical process which causes an electrical current to pass
through a vehicle's cooling system fluid. It can cause rapid damage to radiators and will indirectly cause
problems with other engine components such as water pumps, thermostat housing etc.
It occurs when one or more electrical items, such as a cooling fan or headlight, develops a problem in
its electrical circuitry. This causes an electrical current to seek out an earth path via the radiator core
through the engine coolant.
Stray electrical current can destroy an aluminium or copper/brass radiator in record time.
Aluminium radiator cores have been known to fail within a matter of days, due to stray current.
Many manufacturers and radiator suppliers can refuse to honour a warranty where stray current
corrosion is found to be the cause of premature radiator failure.

Stray current test Procedure:
Note: This check procedure is best carried out with plain water in the cooling system, since coolant may
give a false reading.

1. Remove the radiator cap and run the engine to operation temperature. Do not rev the engine as this may
cause the coolant to aerate.
2.Switch ON all electrical items including items such as a mobile phone, rear demister, driving lights etc.
3.Switch a multimeter to a scale of 5 volts DC or less. Ideally the meter should be capable of reading millivolts.
Do not use a digital multimeter, as its internal operating characteristics are not suitable for this test.
4. Place the negative lead of the multimeter on the battery negative post.
5. Dip the positive lead into the coolant without touching the filler neck or the core of the radiator.
6. A reading of more than .05 volts indicates the presence of potentially damaging stray current passing
through the coolant. Ideally the voltage should be 0 volts, however it is highly possible that some voltage
level will be detected.
7. If no voltage or a very low voltage is detected, carry out the same test as in point 4, but with the ignition OFF.
8. If voltage is detected, isolate the circuit by turning all electrical items OFF and switching each circuit
ON individually.

FIXING OR REDUCING STRAY CURRENT

The best way to fix it is to make sure all the earth points are clean and tight however the cause may not be that obvious, an earth wire on a component may be corroded down inside the insulation of the cable. It's a matter of trial and error and you may never totally eliminate it.
I have also heard of a liquid radiator additive called "stray current arrestor" that was recommended to me by a radiator specialist.

Tony