The process to check the corrosiveness of your cooling system is easy. We have grounded the black probe to the radiator while the red probe is immersed in the coolant. Our multi-meter reads rather high at 385 mV which means this cooling system needs to be drained, flushed, and refilled with fresh coolant.

The world has shifted from brass and copper radiators to aluminum, mainly because brass and copper have become very expensive. With this move to aluminum also comes the threat of increased damage from corrosion. Aluminum is much more susceptible to corrosion because of the very thin extruded tubes used in aluminum radiators. There’s a quick way to check for potential corrosion issues in your cooling system using an unlikely tool – a volt-amp meter.

What we’re talking about here is a process called electrolysis. This is defined as a movement of electrons between two dissimilar metals. The classic example is a lead-acid battery that places two different metals in an acid bath. The result is the rapid movement of electrons between the two different metals which creates a voltage. This same process can occur in your cooling system with a slightly acidic coolant passing through different metals.

All you need in order to check the potential corrosion hazard to your cooling system is a simple voltmeter. We use a digital volt/amp meter set on the DC voltage scale. To check the system, place the negative (black) probe on a suitable ground (not painted) surface on the radiator and place the positive (red) probe in the coolant, being careful not to touch the radiator itself.

The voltmeter will offer a reading in milli-volts of one one-thousandths of a volt (0.001-volt). What this voltage measure is the current flow within the coolant itself. Even with fresh coolant, there will be some electron flow measured in milli-volts. The safe standard is 300 milli-volts or lower.

When the reading is higher than 400 milli-volts, this is generally caused by antifreeze that has expended all of its anti-corrosion additives and has more acid in it. This increased acidity enhances the flow of electrons.

This test can be performed cold but it’s also a good idea to check the coolant with the engine running at normal temperature as well. If you see a major increase in voltage, above 400 milli-volts with the engine running, this may indicate a charging system problem that is back-feeding through the cooling system. This is not a common issue but it does occasionally happen. This can often be solved by improving the ground circuit between the alternator, battery, and engine.

This is a simple test that requires mere minutes to perform and could prevent serious damage to your cooling system and expensive aluminum radiator.