Cooling – Testing For Electrolysis

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One often-neglected task on many cars is the maintenance of the cooling system. In general, most car manufacturers recommend: flush and clean out your cooling system once every 36 months, or approximately every three years. LC Engineering recommends this task should be done at least once a year. The reason is that an old, exhausted coolant can actually cause irreversible damage to your engine components.

A properly maintained cooling system must have a few things in order:

  • Adequate supply of coolant
  • A radiator that acts as a heat exchanger with the outside air
  • A fan or airflow source
  • A water pump to keep the coolant circulating
  • A thermostat to regulate the engine at its optimum operating temperature.
  • The coolant must also have the correct mixture and chemical compounds to promote heat transfer, protect against freezing, and also inhibit corrosion.

To keep your car operating correctly, it\'s important to check the level, strength, and overall condition of the coolant on a regular basis. You also need to change the coolant before it degrades to the point where it doesn\'t perform its job adequately. A fact that we keep hearing kicked around revolves around the reported findings of the U.S Department of Transportation…cooling system failures are the leading cause of mechanical breakdowns on the highway. This is not exactly surprising, since proper cooling maintenance is one of the most neglected areas of most cars.


One failure mode associated with dirty coolant is known as electrolysis. Electrolysis occurs when stray electrical current routes itself through the engine coolant. The electricity is attempting to find the shortest path, and impurities in the coolant often generate a path of least resistance that the electricity travels across. The source of this stray electricity is often from electrical engine accessories that have not been properly grounded. A missing engine or transmission ground strap can also cause the coolant to become electrified. Sometimes the path of least resistance becomes a radiator, a heater hose, or even the heater core. These components are often well grounded, and offer a ground path from the engine to the chassis by means of the semi-conductive path of the coolant. Electrolysis Can Destroy Your Engine Quickly!

Although it\'s semi-normal to have very small amounts of voltage potential in your coolant system, values greater than about a tenth of a volt can start reactions between the coolant and the metal in your engine. In particular, electrolysis affects primarily aluminum engine components, resulting in pitting and scaring of the aluminum surface. This eating away of the metal can cause coolant system leaks, and in particular, radiator leaks around aluminum welds. Cast-iron components are also vulnerable, but typically the aluminum metal parts fail first. On Toyotas in particular, electrolysis can be easily seen attacking aluminum cylinder heads.

The process works somewhat like electrical discharge machines (EDM): These machines work by passing a large electrical current through metal, literally zapping away bits of material until nothing remains. Unfortunately, the electrolysis process works in a similar way, zapping bits of metal in proportion to the amount of electrical current passing through the coolant. A poorly grounded starter can literally destroy a radiator or head within a matter of weeks, depending upon how often the car is started. A smaller current drain, like an electric cooling fan, may slowly erode components over many months.

How can you test for electrolysis?

Other than actually seeing visible signs of erosion, you can perform a current flow test. Connect the negative terminal of a voltmeter to the chassis ground. Test for adequate continuity by touching another point on the chassis - the resistance should be near to zero. With the engine cold and running, submerge the positive probe into the coolant tank; making sure that the probe does not touch any metal parts. The voltage should be less than .10 volts.

During this test, be sure to check the starter. Not only will a poorly grounded starter struggle to turn over the engine, it will also zap away tremendous amounts of metal in your cooling system. Watch the meter carefully when starting the engine. Any voltage spike will indicate a faulty ground connection.

If not, methodically turn off or unplug each electrical accessory until the reading reads below .10 volts. Have a helper switch accessories (like the A/C compressor, heater blower, etc.) while you measure the voltage. If an accessory doesn\'t have an on/off switch, test it by temporarily running a ground from the housing of the accessory to the chassis. Ground each component and check the voltmeter. If the wire restores a missing ground connection to the accessory, then you\'ve found a component with a faulty ground.

The best way to avoid electrolysis is to make sure your engine block and cylinder head have separate grounds to the chassis and or the body. The negative battery terminal should also have ground wires to the body, chassis, and the engine. You an never have to many grounds. LC Engineering recommends using factory Toyota or Delco coolant.