3rd Heater Core?

I have exhausted all of the Google searches on this issue. Exhausted the article write ups. I am lost with this very odd issue.
I’ve installed 3 heater cores in the same 2006 Cummins truck. The first two have failed on the same leg of the core. The outside of the tube corner is paper thin and the aluminum has been ate away like Electrolysis is present. I have flushed the system with Restore Plus and refilled with Fleetguard ES Complete and distilled water. Also, the first and second core were bought from the same parts store. The current core was bought from Napa. I didn’t think about it before, but this time I decided to check for voltage in the coolant. With the multimeter negative going to negative of the battery and the positive going into the coolant, I got a -0.45 VDC. Yes, a Negative voltage. I did move the negative probe to the body and engine. I disconnected the batteries and discharged the trucks electrical system. Same reading. I did test my other 2006 Cummins truck, but I got a -0.76 VDC; This voltage diminished very quickly, where the other truck voltage remained steady at -0.45 VDC with everything connected, Alt disconnected, and batteries disconnected.
Is this something to be concerned about?
I haven’t run the engine but to refill the coolant. Tomorrow I plan to hunt for a small coolant filter to put on the line coming from the head to the core.
Thank you for any input.

 

I can change a light bulb if it isn't high off the ground and that is about all my 'lectrical skills. An old codger told me once when I was working on trailer lights: 1--If you got electrical problems, check your grounds. 2-- If you stiill got electric problems, check your grounds. 3-- If you still got electric problems, check your grounds. 4-- He said anything else was above my pay grade.

 

All of the grounds have been checked and got 0.2 Ohm or better between batteries, body,frame, and engine. This goes for both Positive and Negative.
I did find this article:

http://voltagedrop.biz

 

You can't measure resistance of heavy current connections with an Ohm meter. You need to use voltage drop while the circuit is working.

 

Voltage Drop is the loss of voltage caused by the flow of current through a resistance. Increases in resistance increase the voltage drop. Whenever checking Voltage Drop, current must be flowing in the circuit. ... For instance, a loose or corroded connection can easily add several ohms of resistance to a circuit.

 

I wouldn’t be too concerned about the voltage measured between your coolant and battery ground terminal. The coolant is slightly acidic. The coolant is an electrolyte, and you have dissimilar metals—steel block and nickel plated probe (or Al if you are measuring the heater core). You have created a small battery. Since it was more negative than ground, your probe (or core) is the cathode, and would be getting plated by some of the dissolved ions in the coolant. If you waited a long time, the voltage you measure would slowly approach zero, as the HOAT coolant coats your probe (or the core), protecting it.

I’d look at the other side of the heater core wall thickness. It’s in the cold air supply of your HVAC box. Is any part of it in electrical contact with the firewall as it passes through? Air supply condensate is quite corrosive. It may be a manufacturing process defect that produced a thinner than normal core. Can you try a different supplier?

I hope you have better luck resolving this. It doesn’t sound like fun

 

maybe they are made in china? bad metal. if the stock one is made some where else, better metal maybe. at this point buy the best one made.

 

You are spot on. It is a Type B electrolysis. Basically a battery.
The heater cores have split the rubber/foam material at the firewall. Possibly making contact. I did wrap that one side with electrial tape and insulated the area that has wore through.
Now, I did do a distilled water flush system again. I did mix the ES Complete coolant and distilled water 50/50. I added a pencil anode to the middle plug of the head. I ran the engine to operating temp, drove it, and then checked voltage again...resulting in a -0.013VDC. The only thing I’m waiting on is the VE-Labs coolant filter. I think I will be done with this issue for awhile, hopefully. Thank you for the great input!!