Electrolysis Check

FL335i · April 3, 2016

Decided to check my truck and '89 K5 GMC Jimmy for electrolysis being I've completed my K5's cooling system restoration. I had my wife start both trucks while I was taking voltage readings. Then we went through all the accessories and checked voltage. My '89 K5 passed with flying colors. Engine running everything on voltage was .18V. My truck was at .1V with everything running. During cranking the K5 had .28V and surprisingly my truck had .5V. From everything I've read .3V is the limit. Wondering if other people's trucks have .5V of electrolysis during cranking.

georg · April 4, 2016

Your next step is to check the voltage on the engine block while you crank the engine. Positive lead to block, negative lead to battery negative. You might find a small voltage, 0.2 to 0.3 volts. If so that will explain the voltage you are seeing in the cooling system and you have nothing to be concerned about.

FL335i · April 4, 2016

^ 10-4. I guess the idea is the delta between the voltage on the block and coolant. Everything I've read states .3V max. Even during cranking. Might be the condition of the coolant? My K2 has 41k on it. My K5's coolant has about 3 miles around the neighborhood. And it's green not pink. Pretty happy with what I saw on the '89 K5 today. For as old as that truck is... I've only repaired one ground wire thus far. And voltages were great.

FL335i · April 5, 2016

Georg, interesting info... Yes, I plan on doing some verifying on the block grounding. I'm just wondering if the high voltage during startup is either A- higher than what GM specs and B- if the coolant in my truck is going bad. I am planning on picking up some test strips at Napa when I'm there picking parts for my trans cooler kit.

Brianibew · April 3, 2016

Where are you placing your voltmeter probes?

FL335i · April 3, 2016

Negative probe on the battery Neg post. Pos probe tangling in the coolant. On the K5 the probe is into the radiator and on the Silverado it's tangling in the overflow tank.

georg · April 4, 2016

Electrolysis eats away metal over long periods of time. A small voltage just during the few seconds of cranking is of no consequence as far as electrolysis is concerned.

I would verify that the block is adequately grounded to the battery negative.

OAT coolants (which the Dexcool in your truck is) generate slightly higher voltages than IAT (the green in your Blazer) coolants.

On my truck, with Dexcool in it, I see 30 mV to 250 mV at idle with the positive probe in the coolant in the plastic surge tank (overflow bottle). The voltage keeps varying for no apparent reason.

georg · April 6, 2016

I don't think GM specs a max coolant voltage while cranking, in fact I don't think any body does. That voltage has no bearing on the condition of your coolant.

The test strips I have come across were all for the old school IAT coolants, not for Dexcool.