How To Test For Electrolysis In A Heavy Duty Truck Radiator

Warm the Engine

  • Fill the cooling system to the proper level.
  • Start the engine and allow it to reach normal operating temperature.
  • Ensure the coolant is circulating.

Set Up a Digital Multimeter

  • Use a digital multimeter (DMM).
  • Set the meter to measure DC volts on the lowest voltage scale (typically 12V DC).

Connect the Multimeter

  • Connect the negative (black) lead to a clean engine ground or directly to the negative battery terminal.
  • Remove the radiator cap or surge tank cap (only when it is safe and the system is not under pressure).
  • Carefully place the positive (red) lead into the coolant, ensuring it touches only the coolant and does not touch the radiator neck, filler tube, or any metal component.

Read the Voltage

Interpret the reading as follows:

DC Voltage Reading Condition Recommended Action
0.00–0.20 V Normal. No action required.
0.20–0.29 V Acceptable but monitor. Inspect grounds during routine maintenance.
Above 0.30 V Excessive stray current. Investigate immediately.
0.50 V or higher High risk of electrolysis damage. Repair electrical faults before replacing cooling components.

If the voltage exceeds the recommended limit:

  • Inspect all battery cables and ground straps.
  • Check engine-to-frame and cab-to-frame ground connections.
  • Check the starter ground for corrosion and connection.
  • Check the radiator ground strap (if equipped) connection.
  • Clean corroded or loose ground terminals.
  • Verify alternator output and check for AC ripple, which can indicate a failing diode.
  • Inspect aftermarket electrical accessories (lights, radios, inverters, heaters, PTO equipment, etc.) for improper grounding.
  • Retest the cooling system after each repair to confirm the voltage has returned to an acceptable level.

Best Practices:

  • Contaminated (acidic) coolant will negatively affect the reading and it could be the cause of the electrolysis.
  • Always complete an electrolysis test using new coolant as per the OE vehicle manufacturer’s specifications.
  • Perform the test with electrical accessories turned off, then repeat with headlights, HVAC blowers, PTOs, or other accessories on. A change in voltage can help identify the source of stray current.
  • Include an electrolysis test whenever replacing a radiator or performing major cooling system repairs. This helps prevent a new radiator from failing due to an unresolved electrical issue.
  • Always flush the cooling system before replacing the coolant.
  • Always replace the coolant with pre-mixed coolant or properly mix the coolant with distilled water as per the OE vehicle manufacturer’s specifications.
  • Always flush the cooling system and replace the coolant when replacing the radiator.

A five-minute electrolysis test can prevent premature radiator failure, coolant leaks, and costly engine overheating by identifying electrical problems before they damage the cooling system.

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