Cooling Systems & Electrolysis

[A56]

Since I've ordered parts from RockAuto I've opted to receive their newsletter. I found this interesting:

Your Cooling System & Electrolysis

I have caught myself thinking, "Why did that heater core fail again so soon?" and then discover the heater core was actually last replaced 10+ years ago. (I avoid losing track of time by using my RockAuto account to see when parts were last ordered/replaced. To create an account, go to upper right corner of the RockAuto home page or look under "Menu" on a phone.)

Electrolysis is the likely culprit when "fail again so soon" is for real, and new heater cores/radiators quickly start leaking. Electrolysis eats away metal in the cooling system and the relatively thin walls of heater cores and radiators are the first to fail. There are two primary causes for electrolysis; acidic coolant and bad grounds. An inexpensive multimeter can be used to diagnose both.

Below are some general diagnosis tips/techniques. Visible dark spots on the exterior surface or the heater core/radiator can be another sign of electrolysis. Consult your vehicle's repair manual (found under "Literature" in the RockAuto.com catalog) and/or seek the advice of your spouse, mechanic, attorney, etc. for more specific instructions.

Typical Multimeter, Radiator & Heater Core
Acidic Coolant:
Old coolant can become so acidic that it begins conducting electricity and moving metal like the acid in a car battery. Take the radiator cap off the cold radiator (so no pressure builds). Start the engine and allow it to warm up enough for the thermostat to open and coolant to begin circulating through the cooling system.

Switch the multimeter to one of its lowest DC voltage settings. Stick one electrical probe in the coolant and put the other probe on the negative battery terminal. A reading of 0.4 volts or above indicates electrolysis is likely happening.

Loose, Missing or Corroded Electrical Grounds:
Now with the engine off and the battery disconnected, again stick one electrical probe in the coolant and put the other probe on a metal engine part (ground). If the voltage is still 0.4 volts or higher with the battery disconnected then old acidic coolant is indeed the culprit and should be flushed and replaced.

However, if the voltage reading is 0.00 with the battery disconnected, then there is a bad ground somewhere in the electrical system. Corrosive electrical current is being misdirected through the cooling system.

Solutions:
Acidic coolant should be flushed out of the cooling system and replaced with the correct new coolant (find Coolant/Antifreeze under "Cooling System" at RockAuto.com). It is often good to flush the system more than once to thoroughly remove as much old coolant as possible.

To track down bad grounds, try measuring the coolant's voltage while turning electrical accessories on and off one at a time. A change in the coolant's voltage reading may indicate the accessory (radio, fog lights, etc.) needs its grounding point cleaned, replaced or relocated.

I never know for sure if it helps, but when possible, I wrap pieces of wire around both the heater core inlet and outlet nipples and then attach both wires to the same piece of grounded metal in the engine compartment. My theory is that any stray electrical current will immediately go to ground rather than passing through the heater core.

Tom Taylor,
RockAuto.com

 

[Murray]

Not sure of other models but '67-'69 cuds's already have a factory ground strap on the heater core.

 

[67Dart273]

One of the biggest problems for cooling systems is just plain crap water. When I was in the Navy in San Diego you would lose a rad at the click of your fingers if you were dumb enough to use tap water in them.

 

[Scody21]

Worst thing you could do is use plain old tap water. I used distilled water and Redline water wetter only in my car. Also been known to use bottled water, but never tap..

 

[RedFish]

Not sure of other models but '67-'69 cuds's already have a factory ground strap on the heater core.

Yep, and little ground strap from chassis the engine block but that still wasn't nearly enough ground path. Try this on... 1st 67 B'cuda we bought was a slant 6 notch, in summer 1981. I Looked it over, drove it, traded for it. First ride out after dark I realized this was the weakest charging system I had ever owned. Stop at a red light and headlights would dim, sit long enough and turn signals would slow. Amp gauge says discharge, dash lights dim, heater blower slower, but... This old girl doesn't have a spec of rust anywhere.
So as time has went on, I find a lot more ground wires on the new cars with all their electronics. Their aluminum radiators hold up much better than the rubber seals at plastic tanks. I have 2 1996 Camrys here with nearly 300k miles and neither has needed a heater core.
To this day I still wonder did lesser positive ions traveling through that 67 chassis help save it.

 

[Bewy]

When I had a custom made alum rad made 20 yrs ago, I had a ground lug welded to it. Since the battery is nearby, I ran a wire direct from the lug to bat [-] terminal. No corrosion, but I do use pre-mixed coolant with corrosion inhibitor.