What is and how to detect STRAY CURRENT …

Stray currents in the cooling system
In simple terms stray current is a chemical/electrical process which causes an electrical current to pass through a vehicles cooling system fluid.
It can cause rapid damage to radiators and will indirectly cause problems with other engine components such as water pumps, thermostat housings, etc.
This is brought about when one or more items such as a cooling fan or headlamp 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.
The most common fault is the body/battery earth lead being loose, dirty or not in place.
That is what it is , now for the test prodedure.
The procedure employed to test for Stray Current is:
1. Remove the radiator cap and run the engine to operating temperature at idle speed.
2. Switch ON all electrical circuits including items such as a fan, rear demister, head lights, radio, wipers etc.
3. Attach an ANALOGUE multi meter. Set meter to volts. Use as low a scale as you can.
4. Connect the negative lead of the meter to the battery negative post.
5. Dip the positive lead into the coolant without touching the filler neck.
6. Test the coolant – if the READING above 0.5V, there is stray current present. 0V is best.
7. If no reading, there is no Stray Current was present. to continue if stray current is present;
8. Systematically, the electrical system is tested by turning electrical circuits OFF individually and testing the meter prior to turning off the next circuit.
9. After all circuits were turned off, and stray current is still present. continue.
10. At this stage a temporary earth lead can placed between the battery negative post and the body.
11. Immediately the circuit should test free of stray current.
12. Remove the temporary earth lead and stray current will be noted noted in the cooling system.
13. The battery to body earth cable is to be inspected.
14. If necessary, make up a new lead out of 6mm cable and secure it from the battery neg post to the body or radiator itself. Make sure you remove paint from the body to ensure a good contact.
15. Retest and there should be no SC.

Remember, Stray current is instant death to aluminium radiators and brass alike. Aluminium will corrode 253 times faser than brass. !!!!!
Some important notes:

  • Brass does not transmit heat as well as Aluminium.
  • NEVER mix coolant types.
  • Always flush with good clean water prior to adding good quality additives.

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