Well my heater core started leaking a couple weeks ago, and I've been driving around with it bypassed for a while now. I got around to buying a new one, and the instructions stressed making sure everything was in proper order and that there was no electrically induced electrolysis going on, that it would void the warranty. Well anyway, it says it should be less than 0.1V between the positive in the coolant, and the negative on the negative battery terminal. My question is, what does it mean when there is a negative voltage? I have -0.25V between the radiator and the battery, and that has me confused. I know it is supposed to be less than a value, which a negative number is, but should it be closer to zero? Should I even be concerned at all? This is the second heater core I have installed since owning the truck; the last one went around 5 or 6 years before it started leaking, while the (presumed) stock one lasted 12 years. Since I've had the truck, I have added two amps, which are the only things that didn't come grounded from the factory. Should I worry about this, or just flush the cooling system and install the new core and go about my business as usual?

 

Cars and trucks have aluminum, iron, copper, brass and lots of other metals wetted by the coolant. This multiplicity of metals and their consequent galvanic action makes the coolant's anti-corrosion additive package work hard, at least until it's exhausted. Add in a stray electrical current, and you've got problems.

Here's a quick check for stray voltage. Set your high-impedance voltmeter to a low DC voltage range, and connect the negative probe to a good ground on the engine or to the negative battery post. With the engine cold, remove the radiator cap. Insert the positive probe into the liquid coolant through the radiator filler neck--but don't touch the filler neck or the fins. Start the engine. Hold the probe so it contacts only the coolant. A voltage reading of more than a few millivolts could be the source of your problem. Engine manufacturers have reported issues with aluminum-alloy engines with sustained voltages of 15 millivolts. Repeat this test with the meter set to the low AC voltage range. Turn the engine off before it heats up enough to boil over and cook you like an Easter egg.

Where is this stray voltage coming from? Check ground straps and connections for excellent electrical contact. Marginal-looking ground straps should be replaced, then connections cleaned and tightened, and covered in Vaseline, lithium chassis grease or dielectric paste to prevent moisture-driven corrosion

 

I checked the DC voltage as you described and saw -.25V (engine running at idle). I don't understand why it is negative. If there was stray current through the coolant, it would be a positive voltage, correct?

 

Anyone else?

 

Reverse the probes. Then it will read positive.

 

I know that. I am familiar with electricity, but the chemistry of electrolysis has faded away from my classes a few years ago. I went through the proper test procedure: Positive in the water, negative to the battery negative terminal. Why is the voltage reading negative, and what does that mean in terms of electrolysis? With a negative voltage, I know that there is no stray voltage in search of a ground; it's opposite of that. What I'm unsure of is whether or not this negative voltage will have the same effect as a positive voltage.

 

Any stray voltage is bad.
The age old question.
Does current flow from + to - or the other way?

 

Here is a link that clearly shows a negative reading.



http://www.popularmechanics.com/auto...c/1363277.html

 

Good point about the direction of current. It seems that each thing I read on the subject gives a different threshold of allowable voltage. It doesn't seem like there is any strange current in the coolant that would be seeking a ground, as that would show as a positive voltage, correct? 15 millivolts seems awful low (.015 V) as I am around -.25V. I will try cleaning all the ground connections and see if I can get the reading to change any. Thank you for your help and the link. I've googled it and never came up with anything that answered the questions I've had. One last thing, is the threshold for allowable voltage the same for the test on AC voltage?

 

You will probably have to replace all the coolant.
They recommend a distilled water / antifreeze mix.

 

Yeah, I was gonna flush the system before installing the new heater core.

The distilled water brings up another thought/past experience. The judges at the design competition I'm a part of (Formula SAE) asked about our coolant water last year or the year before. We told them we were using distilled water, and they brought up electrolysis and that with the distilled water, the metal would be eroded, albeit very very slowly. Then the other side of the story, tap water, would leave deposits in the system. They were asking how we decided on one or the other. I don't know what reasoning we finally came up with, but I remember them asking about it.