Jim Grant's Tech Tips
Electrochemical Degradation
Q:
I've read about electrochemical degradation causing cooling system failure. It seems to be a hidden problem with some vehicles which causes radiator failure. I read a car-care article describing how to check for stray voltage using a DVM. So I took some measurements. I put the negative probe on the engine ground and positive in the coolant of the surge tank of my 2005 Chevy Equinox. I measured +200mVDC with the engine off and about +240mVDC with it running. The engine was only cool to warm when I did this cautiously. Is this too high of a voltage? Will this cause problems with my cooling system in the future? What can I do if it is a problem?
A:
Electrochemical degradation of the cooling system is a problem in today’s vehicles; this chemical reaction is called electrolysis. Electrolysis involves an ion exchange between the coolant and the components that the coolant contacts, which eats away at the heater core, radiator and engine material. The most common cause for this condition is due to coolant acidity. Also bad electrical grounds on the engine or body of the vehicle can create this erosive condition. To correctly check for the potential of electrolysis the engine has to be running, at about 2000 RPM, at operating temperature with the coolant flowing or the readings will not be correct. Place the negative probe of the voltmeter on the negative battery post and place the positive probe in the coolant. Make sure that the positive probe is only touching the coolant. If the voltmeter displays 400mv (.4v) DC or greater then the cooling system needs to be flushed. After flushing the system be sure to check the coolant again. It is not uncommon to have to flush the coolant more than once to sufficiently cleanse the system. If an elevated voltage is still present then the electrical system of the vehicle has to be checked for ground integrity. I’ve even seen the need for additional grounding straps to get an electrically challenged vehicle back in line.
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