Testing antifreeze with a multi-meter

[koda2000]

Anyone ever try this?

Using a digital multi-meter, remove your radiator cap and place the positive lead in your antifreeze. Connect the negative lead to the negative terminal of your battery. Read the voltage, 0.4 volts or less means antifreeze is okay. More than 0.4 volts means antifreeze should be replaced.

It is suggested that in severely neglected cooling systems, high voltage can basically turn your cooling system into a sort of battery, which can even effect engine electronics.

Note: This test has nothing to do with checking the effectiveness of your antifreeze. To to this, use an antifreeze hydrometer.

 

[Indispensable Explorer]

Never tried it, however I have heard that if the voltage reading is high it will corrode your engine more quickly.

 

[drdoom]

Koda I have never even heard of that. Thank you.

 

[Josh P]

Never tried it, but I will. Thx for the info

 

[Prince_Polaris]

Yeah I've never heard of this either bu5 I'll certainly give it a shot later on once the weather calms back down!

 

[Larryjb]

I've heard of this before. It was more of a test to check for the possibility of electrolysis taking your heater core out. I do recall that the maximum allowable voltage was in the millivolt range. 4 V seems awfully high.

A more important test is pH. Coolant is designed to be somewhat basic (pH around 8). As air mixes with the coolant and oxidizes the glycols and other components, it turns them into acids. Coolants contain buffers which protect against these acids, but over time the buffers get used up. After a few years, there's not more buffer available to protect against the acids, and the pH turns acidic (below 7). The swing from basic (pH ~8) to acidic (pH ~4) can happen quite rapidly once it occurs. Acids will eat up aluminum and other metals. This can include water pumps, heater cores, radiators, etc.

I have a 1992 Grand Marquis and I used to keep the coolant changed regularly about every 2 years. When the car was about 15 years old, I still had the original cooling system including the water pump, radiator, heater core etc. Then I got lazy and didn't change the coolant (the old green stuff) for about 4 years. The pH had dropped to pH 4 or 5. A year later my water pump went, and a year after that my radiator went. Coincidence? I don't think so.

Larry

 

[koda2000]

Oooops, You are correct Larryjb. It should have read 0.4 volts and not 4 volts. I missed the decimal point. I'll edit the posting. Thanks.

 

[Indispensable Explorer]

I've even heard .3 is too much.

 

[BrooklynBay]

Is the reading the same for all coolants (ethylene glycol, propylene glycol, and Dex-Cool)? What about if the coolant has additives such as sealants or if the mixture is another ratio other than 50/50?

 

[Larryjb]

In general, you want the voltage reading to be as low as possible. The reference I saw regarding the millivolt reading for coolant came from the 4.6L Grand Marquis/Crown Vics of the 90s as a reason for corroding heater cores. One of the reasons for this voltage can be poor grounding of the engine block to the body. When the spark plug fires, it grounds to the block, then through to the body, to the battery ground. If the engine ground is corroded, the block grounds through the coolant instead, the reason for the increased voltage in the coolant. Ford's solution was to add as ground strap from the heater core to the body, to keep the heater core at the same voltage as the body. If I got a high voltage in the coolant, I'd check the grounding of the block by measuring the resistance between the block and the body. Practically, I figured that as long as my voltage was around 0.3-0.4 V, it was probably fine. If the voltage got up to 0.7-0.8 V and above, I'd begin to get concerned. It's not the coolant that's bad, it's the source and grounding of the voltage that's the concern.
As for pH, all coolants must maintain a basic pH (>7). Usually, it is kept in the range of 8 and higher. The normal way to control pH is to use what chemists call a buffer system. GM uses carbon based buffers (Dexcool), while G-05 uses borate buffers. The old green coolant used silica based buffer systems, I believe. Be careful, though, a lot of "green" coolant acutally contains GM's carbon based buffers. It gets quite confusing when you're in the aftermarket coolants.

Testing coolant colour, well, if it looks bad, it's been bad for a looooong time. I'd be hesitant to purchase such a vehicle because it's probably been eating away at water pumps, radiators, heater cores, etc, for quite awhile already. As far as I'm concerned, the only reliable test for coolant is the pH paper. The freezing point and boiling point is probably not far off as long as it was filled with the correct ratio in the first place. The coolant will go acidic before you lose freezing and boiling point protection.

Larry

 

[Centaurus5.0]

Good info here! Thank You.

My rig sat for 3 years before I bought it. First thing I did was change all the fluids except the coolant because it "looked good". Still bright green, no chunks floating it it, full shadetree DIY expert anylsis. 3,000 miles later the OEM water pump blew out on my next trip to Florida. That was around 60,000 miles.)nly had 57,000 original miles when I bought it. I was a bit confused considering I've seen OEM pump go 150,000+. As you've expained, time, not miles, is what matters for coolant.

I use this now:

http://www.norosion.com/

No-Rosion Cooling System Corrosion Inhibitor

Originally developed for high-end boilers and cooling towers in the field of industrial water treatment, No-Rosion is a powerful, industrial-grade automotive cooling system corrosion inhibitor that stabilizes coolant pH, and protects all six metals most commonly found in cooling systems from corrosion and electrolysis - including aluminum.
Dissolved oxygen in coolant functions as a catalyst that drives oxidation of metals in a cooling system. No-Rosion contains oxygen scavengers that chemically remove dissolved oxygen from coolant, thus preventing this type of damage.
Polymer dispersants in No-Rosion prevent hardness in water, and inhibitors in antifreeze, from dropping out of solution to form gels. These insoluble materials adhere to surfaces inside a cooling system to form scales and deposits that cause overheating. These polymers also provide lubricity to the water pumps. For this reason, it is not necessary to use a water pump lubricant when No-Rosion is in a cooling system.
For heavy duty/diesel applications, No-Rosion contains nitrite, which prevents cavitation erosion of wet-sleeve cylinder liners. Proper use of No-Rosion extends coolant life to five years. This reduces the frequency of draining and flushing toxic used coolant. Not only does this save you time and money, it also protects the environment.


Another big problem people have on 5.0L's anyway is the water pump bolts that go through the coolant snap off in the block due to corosion (from overdue coolant changes).

I think 2-3 years coolant changes are a smart idea considering how important the system is and how much can go wrong when left bad. No more broken WP bolts or bad heater cores.


Your title made me wonder if you can do a voltage test with the brake fluid consider the standard test tests the copper content (corosion). Enough copper would effect voltage no?

 

[drdoom]

New coolant yesterday: 0.11VDC

 

[imp]

@Larryjb "As air mixes with the coolant and oxidizes the glycols and other components, it turns them into acids. "

Good points! Air should not normally be mixing with the engine coolant, and in the case of 3rd. Gens the whole system is pretty well closed up. The "radiator cap" is on the overflow catch bottle, thus the only air in there is the cushion in the bottle, and it's stagnant as hell. Pure water of Ph = 7.0 is said to be non-conductive to electricity. Unfortunately, water exposed to air for even a very short time quickly assumes a Ph of 6 or less, due to CO2 in the air dissolving in the water, making it acidic, because of formation of H2CO3, Carbonic Acid. Acid eats away at things made of metal. The Ph of carbonated drinks is typically < 4.0.


Measuring voltages as mentioned uses the electrolysis going on in the cooling system as a gauging means. Another way might be to measure the DC resistance of the coolant itself. Either way, I THINK, emphasis on that, measuring the Ph of the coolant would be a preferable way of checking it. Keeping it at 8.0 or a little higher, would be a good idea. FWIW, I checked the cooland Ph in my 2004, the stuff has been in there since day ONE, and it was 7.6! So, I left it alone. Lazy old man...... imp

 

[Larryjb]

I wasn't thinking about the CO2 -> carbonic acid. That's a great point too.

Given that automotive coolant has a pH >8, the solution is already ionic and will conduct electricity, so I wouldn't base the coolant on DC resistance. As you say, we must emphasize the importance of pH testing coolant. If your coolant is 7.6, it's very close to becoming acidic. IMHO, I'd get it changed soon.

Electrolysis will likely be between the aluminum in heater cores, water pumps, and intake manifolds, and the iron block. Aluminum would be eroded away in this reaction, preserving the iron block. This electrolysis voltage could be as high as 1.2V. If you have anything above 0.3 or 0.4 V with the engine off, I'd say that's the beginning of significant electrolysis. If it goes higher with the engine running, I'd say you've got bad grounds to the block. Coolant, in addition to the buffers to keep the pH >8, must contain rust inhibitors that coat the metal surfaces which will block electrolysis and prevent the aluminum from eroding.

 

[imp]

@Larryjb
You know your stuff! Study Chemistry? I never really thought much about it, but aluminum blocks and heads must surely throw a whole new light on the electrolysis problem. Now, if only there were no dissimilar metals in there.........imp

 

[Larryjb]

Gee, how'd you guess? (masters in chemistry)

I also recall that, if the inhibitor coating were lost, perhaps to an overly extended interval, it takes a few months for a new coating to establish itself once the coolant has been refreshed. Therefore, I'd expect that, if electrolysis was present due to an such an extended interval, you'd still be able to measure a voltage due to electrolysis for a few months, gradually diminishing over time.

I'd be curious if there were less electrolysis in aluminum block motors. Anyone with an aluminum block out there that can test this? It should be with the engine off because I'd want to be sure that the source of electricity is the electrolysis, not poor grounding.

 

[imp]

I have seen in years past, when cast iron water outlet necks were changed to aluminum, instances where the outlet had been eaten through and leaking. Same for steel nipples used as connection points for heater hoses. Outlets are now often plastic. Radiator tanks, too. If plastic could conduct heat adequately, maybe the whole damn engine and accessories could be made eliminating metal altogether! imp

 

[robertoa1a]

Great advice.