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galvanic action between the dissimilar metals of the engine, with the water in the cooling system acting as the electrolyte is going to give you some stray, ultra low readings. are you losing metal in any of the engine parts? water pump housing showing pitting? if everything else is properly grounded, you might try a sacrificial anode, to help reduce the number, and to fight against corrosion of radiator or engine parts.

Testing for Stray Current in the Cooling System

Another BIG factor in corrosion is stray voltage in the coolant. This causes corrosion even when the coolant is in good condition. If the engine does not have a good ground connection, voltage from the charging system will flow through the coolant to ground, creating and speeding electrolytic corrosion.

One needs a voltmeter (multimeter) with a scale capable of reading in millivolts. (I use those with digital read outs.)

1. Empty the vehicle of coolant and flush with clean water.

2. Fill the cooling system with distilled or demineralized water. (A coolant filled system gives inaccurate readings.)

3. Connect the voltmeter to the battery ground and the positive terminal into the coolant making sure not to touch the metal core or filler neck).

4: With the ignition on and again with the engine running, turn on every component. While you are monitoring the presence of stray voltage in the cooling system, have a fellow worker operate the brake lights, parking, head and high beam lights and everything you can't turn on while you're monitoring your voltmeter.

5. Note any voltage and any increases in voltage and what component increased it.

Your system has failed if you get a reading above 50mV (0.05 volts) The source (s) of the current leakage should be found, as they can destroy a radiator or other components in a short period of time, depending on the level of voltage.

The system is fine if your voltmeter reads below 50mV (0.05 volts) so refill your cooling system with coolant.

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I've already used this process - that's how I know I have .7 VDC.

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then it seems time to check/install grounds for good connections, and add that sacrificial anode. disimilar metals with a liquid between them, are going to create tiny amounts of electricity. send the strays into an anode.

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High school chemistry was a LONG time ago but IIRC pure water ie distilled water would make a better electrolyte than tap water would so you might actually be making it worse. This stuff http://www.fleetguard.com/html/en/products/cooling/coolant/supp_add.html is what I use in my N14 Cummins to keep the cooling system from eating the engine alive. You can get it at any big truck dealer like Kenworth etc.

Kevin

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ago but IIRC pure water ie distilled water would make a better electrolyte than tap water would so you might actually be making it worse.

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Sounds likely, but is the additive clear? Can't run anything but water at the track any more unless that has changed. It's been a while since I ran the car. I've bookmarked the product - thanks!

Edit - I just read more and it only works with glycol based coolants, so it won't work with just distilled water.

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High school chemistry was a LONG time ago but IIRC pure water ie distilled water would make a better electrolyte than tap water would so you might actually be making it worse. This stuff http://www.fleetguard.com/html/en/products/cooling/coolant/supp_add.html is what I use in my N14 Cummins to keep the cooling system from eating the engine alive. You can get it at any big truck dealer like Kenworth etc.

Kevin

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Sounds likely, but is the additive clear? Can't run anything but water at the track any more unless that has changed. It's been a while since I ran the car. I've bookmarked the product - thanks!

Edit - I just read more and it only works with glycol based coolants, so it won't work with just distilled water.

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.... I'm still baffled by the fact that I have voltage with the battery disconnected and sitting 10 feet away. The only capacitor in the car is the MSD and that was unhooked too.

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I believe that is like static electricity built up in the system from the movement of fluid throught the cooling system.

I just went in the garage and checked mine. I run distilled water, Justice Brothers Cooling System Protector, and Justice Brothers Super Radiator Cool. That's it.

New rebuilt motor with 800 miles: aluminum heads, aluminum radiator, aluminum water pump, brass heater core, cast iron block. I went for ride earlier so the fluid temperature was still at 104 degrees per my laser themometer....

76.8 millivolts or .077 volts



New motor and I spent a TON of time and effort cleaning and chipping rust scale out of the block. So the fluid is tiny tiny bit brownish from loose stuff I couldn get out or got loose since startup. Should flush it.