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Electrolysis Corrosion in the Cooling System

Radiator hose

When a heater core, radiator, or other cooling system component fails through corrosion from the inside, there's a good chance that electrolysis corrosion is to blame. Today's systems with their abundance of aluminum parts and coolant formulas that haven't changed in decades can sometimes clash. Most engine coolants ("anti-freeze") in use today include corrosion inhibitors to prevent electrolysis corrosion from happening. This doesn't mean it won't.

Changing the coolant in your engine and radiator regularly is important as it replaces those worn down electrolysis inhibitors. Proper maintenance of electrical components on the engine, especially ground wiring and connections, is equally important.

How Electrolysis Corrosion Happens

The basic gist is simple: your engine's coolant, or antifreeze, has an acidic component or constituents to it which are responsible for the anti-freezing properties of the coolant. Something that's vitally important in cold weather. Other components to help lengthen the lifespan of the coolant as well as aid its temperature absorption and dispersion properties may also be at play. These same components, however, can cause electrical current in the antifreeze as it moves around the engine and its molecules rub against one another. In addition, electricity from the engine's components themselves can add to this current flow.

Inhibitors in the coolant normally keep this from happening, or at least mitigate its effects enough that it is not a problem. When the inhibitors break down or are overwhelmed by too much current, usually due to a ground failure in an engine component, things can get problematic.

Many of today's car engine parts are made of aluminum, including the engine block, radiator, water pump, heater core, and more. Aluminum reacts with electrical current and some aluminum alloys, which are common in some vehicle components, can break down when exposed to electricity and acidic items such as coolant.

This electrolysis corrosion can lead to leaks and parts failure. The most common place to see it is in an aluminum radiator or heater core that's sprung "pinhole" leaks. These pinholes are from weak points in the radiator's build wearing away through the electrolysis corrosion process.

Diagnosing the Cause of Electrolysis Corrosion

Finding the cause begins with two lines of inquiry. Begin with the coolant itself: is it old? Worn out? Ready for replacement?

If the engine coolant hasn't been replaced in some time, flush and replace it after repairing whatever the corrosion may have broken.

Next, begin looking for stray electricity entering the coolant. This is usually from a bad or worn ground that goes to the engine block (core) or a railing connected to it rather than to the frame or body. Common items here include the alternator, starting circuit, or the battery itself. All grounded components should ground to the vehicle's frame, not the engine. Loose connections or mis-wired items are likely problems when grounding goes to the block instead.

Check all major engine ground straps for corrosion or loose connections. Repair/replace as needed.

Something as small as a sensor grounding to the fuel rail could be to blame. The fastest way to find a ground issue is to put a multimeter on the engine block as the engine is running and read for current. If it's found, the amount of power (volts, amps) may point to the most likely cause. Higher readings mean something major such as the alternator or battery. Smaller readings could be small components like sensors or small components.