WHY ALL THE CORROSION?

IT MIGHT BE ELECTROLYSIS

Radiators and heaters have undergone considerable improvement. And we have had superior antifreezes in recent years (even before the introduction of the orange organic acid type). So it seems hard to believe that so many radiators and heaters fail from inside-out corrosion and perforation. Of course, vehicles are being kept in service much longer (thank high sticker prices for that), so eventually even better systems will fail. But in addition to low antifreeze protection and depleted inhibitors, there are other specific problems that  contribute to the perforation failures.

 The most significant is electrolysis — the flow of stray current that gets into the coolant and flows through the radiator (even along the radiator hoses) and through the radiator core to electrical ground. Although electrolysis is a single problem, it has many possible causes.

 When a radiator fails in a short amount of time/mileage, and you know the coolant was a recently installed name brand, check for electrolysis. Ground the negative lead of a digital voltmeter to the battery negative (ground) post or side terminal, then insert the positive lead into the coolant itself (making sure the tip doesn’t touch a metal neck or core of a radiator). If you get a reading of 0.3 volts or higher, that’s excessive electrolysis — bad news. Older cast-iron engines could tolerate that, but the modern engine with all its aluminum components cannot.

 One of the worst cases we saw occurred in just 30 days and under 3000 miles.  In that one, the problem was an auxiliary horn had been installed and grounded to the radiator support. So if a vehicle recently had an electrical accessory installed (don’t forget anti-theft alarm systems), check the grounds.

 Although the most severe results occur if the part is bolted to the radiator or its support (such as a radiator fan motor), the modern electrical harness is so complex, the source could be something in the rear (remember all those sport utility vehicles and minivans with their rear HVAC systems).

What you should do is check the voltage as each electrical device is turned on. Because the radiator electric fans are a primary suspect, start with them. Just remember that many vehicles have dual fan systems, and testing just one fan isn’t enough. On the typical setup, you can trigger each fan with a jumper wire to ground the particular fan relay. The relay is wired to the power-train computer on most systems, so unplugging its connector and hot-wiring directly to the fan motor may be a safer approach. Be sure to check the coolant voltage with the engine cranking, as the starter ground circuit is another strong possibility.

 If a circuit seems to be producing an unacceptably high stray voltage through the coolant, as a follow-up test, try installing a jumper wire as a second ground, to see if the voltage drops. If that works, check the existing ground and if it seems to be good (or the voltage reading doesn’t improve after cleaning and tightening the ground), make a permanent installation of a second ground wire.

Produced by the National Automotive Radiator Association (NARSA)