font size print send to a friend

Stray currents

Home Motoring About my car Car components Stray currents

Send this page to a friend
Friend's email
Your email
Your message

RAC is aware of instances where radiators or heater cores have been destroyed within weeks of being replaced.

The problem is often misdiagnosed by the repairer as stray currents in the coolant caused by poor earthing. In many cases it is more likely that poor repair practices are the real cause of the problem.

Stray currents

The issue of stray electrical currents in vehicle cooling systems is controversial.

• The theory is that return currents from electrical components such as lights, radios etc travel through the cooling system coolant on their way back to the battery.
• This is believed to cause corrosion of metals in the current's path, similar to the corrosion that occurs when you place two different metals together in water.
• Although many repairers believe that stray currents are a major cause of corrosion in engine cooling systems, there is no hard evidence to support this.

Prevention 

Modern engines use a range of alloys in their construction.

• The correct chemical balance of the coolant is essential to prevent these alloys corroding.
• It is vital that:
  • The correct coolant, as recommended by the vehicle's manufacturer, is used.
  • The cooling system is properly maintained and the coolant changed at the recommended intervals.
• If repairs are required, the correct repair procedures, as recommended by the vehicle manufacturer, are used.

Repairs

If your cooling system requires servicing or repairs:

• Obtain a quote for the cost of fixing the fault from a reputable repairer. 
• The quote should:
  • Give the total cost of repairs including parts and labour.
  • Detail the work to be carried out along with any specific exclusions.
  • The quote should include flushing the cooling system thoroughly as recommended by the vehicle's manufacturer and adding the manufacturer's recommended coolant.
  • State when the work can be done and when it will be completed.
  • State what guarantees apply.
• When requesting a quote you should ask for the cost of the cooling system to be repaired. You should not be any more specific.
• Don't ask for the radiator to be repaired or replaced. If the radiator is not the cause of the fault you may have to pay for additional work to find the real cause of the problem or any subsequent failures that occur blamed on stray currents.
• If you feel that the quote is excessive or you are unhappy about the content of the quote, you should obtain a quote from a different repairer.
• When you are satisfied with the quote you can authorise the repairer to proceed with repairs. You should obtain agreement from the repairer that any additional work, that becomes apparent during the course of the repairs, must be discussed with you and authorised by yourself before proceeding.