Cooling System Maintenance

Tools / Equipment Required
Voltmeter with a scale able to read in millivolts (Analogue voltmeter is preferred).
Or a radiator industry designed stray current detector (present to 50mV).  Target range below 50mV.
However any voltage reading in the cooling system should be corrected as further deterioration
will cause major damage.


  1. Connect the voltmeter or current detector negative terminal to the battery ground and the positive terminal directly into the coolant (ensure not to touch the metal core or filler neck).
  2. With the ignition on and again with the engine running, check EVERY component. Whilst you are monitoring the presence of stray voltage in the cooling system, have a fellow worker operate the break lights, parking, head and high beam lights and check for any increase in voltage readings in your voltmeter.

If you get a reading about 50mV or a red fail light on the current detector.
Do Not Proceed
The source of the current leakage should be found, as this can destroy a radiator in a short period of time (hours or days, depending on the level of the voltage) and severely damage other engine components.
It is highly recommended that all repairs or work carried out on a vehicles electrical system or component be carried out by a qualified auto electrician.
Note: The cooling system cannot be successfully passed as being free from stray current voltage if the system contains coolant, it has been found that coolant may provide inaccurate readings.
Only when the analogue voltmeter reads below 50mV or a green pass light is obtained should you proceed to fit a new radiator or recharge a cooling system with coolant.
In both cases the flushing procedure should be followed prior to the vehicle being released.See notes of flushing below.
Note:  Some coolants have been known to retain an electrical charge after the fault has been detected and repaired.  All testing for stray current should be carried out using clean water after the flushing procedure has been carried out.  It would be very wise to test the vehicle again in one or two days to ensure stray current related problems are corrected and coolant has settled down.

Cooling System Flushing Procedure
Because coolant/inhibitors from different manufacturers have different chemical compounds which may adversely react if mixed, it is important that you DO NOT create a chemical cocktail within your cooling system by mixing different brands of coolant/inhibitor. 
Even though the coolant had been drained from the system, the inhibitors remain affixed to the cooling system components and must be chemically removed, using a quality alkaline flush.


  1. Ensure the cooling system is sound and free from leaks and check all components for wear and condition.  If need, replace worn components.
  2. Choose a quality alkaline cooling system flush (500mL per 12 Litres).Observe the instructions on the container.
  3. Replace the radiator cap and run the engine at operating temperature for 15 minutes in a 4 cylinder vehicles and 30 minutes in 6 or 8 cylinder vehicles. (Ensure the vehicle heater is turned on).
  4. Drain and rinse the cooling system including the overflow bottle and heater core. At this point a power flushing machine may be used if this equipment is available. and/or Rinse the system with clean water until you are convinced that the only fluid remaining in the system is clean water - RINSE - RINSE - RINSE (this may need to be refilled and drained a number of times).
  5. Refill the cooling system using clean water to perform a stray current check.
  6. Do not add coolant at this time until a complete stray current check has been performed (refer to stray current procedure on previous page).  The presence of stray current will deteriorate the cooling fluid quality immediately. 
    Always ensure you select a coolant/inhibitor that meets the vehicle manufacturers recommendation or the one that meets AS2108-97 Type A or Type B whichever is recommended as being in support of the vehicles manufacturers recommended 
    coolant performance standard.
  7. Ensure the correct concentration of coolant/inhibitor is used, as overdoing or underdosing will have a direct effect on the performance of the cooling system and the life of the components including the radiator.
  8. Only after the vehicle has been cleared of the passibility of stray current (electrolysis).
    Rebuild the cooling fluid by first adding the selected products then topping up with clean water (demineralised ro distilled water), or use complete fill as required.
  9. Mix a portion of the coolant for the owner to use for topping up coolant level.