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Checking Automobile Coolant

From the Expedition Mailing List:

On Jan 16, 2009, at 11:18 PM, Dean Eveland wrote:

Coolant ideally is designed with a buffer to counter acid
conditions, but the coolant has to be changed before the
buffer wears out, usually a couple of years.
Some coolants are more like alkaline mixtures than buffers, and
are hard on aluminum engine components.

An interesting test is to check the electrical potential in your
coolant. Connect two rods of dissimilar metals (like a steel nail and a bronze
brazing rod) to the leads of a voltmeter and insert them into the
coolant. I saw an old tech instructor demonstrate the effect years ago.

Google retrieves lots of articles. The Wikipedia article is a start,
and mentions product liability litigation against GM products.


On Jan 17, 2009, at 12:33 AM, Keith Veren wrote:

Well, Dean, what is the answer?? If your coolant posts a charge is it
bad? What if it does not?


Hi Keith,

I'm no expert, so I'll paste what was written in another forum:

“You can also use an ordinary digital volt meter for the same purpose. With the engine off, touch the voltmeter positive test lead to the radiator or engine (making sure you get good metal-to-metal contact). Then open the radiator cap and insert the negative test lead into the coolant. A reading of up to 0.2 volts is considered acceptable and indicates the presence of reserve alkalinity in the coolant. If the coolant reads 0.3 to 0.6 volts, it is borderline and should be recycled or replaced. A reading of 0.7 volts or more would tell you the coolant is overdue for a change.

Internal corrosion in the cooling system can occur regardless of the condition of the coolant if voltage from various accessories (alternator, starter, ignition, etc.) flows through the coolant to ground rather than follows the intended ground path through the ground strap between the engine and chassis or the ground cable between the engine and battery. You can check for this condition by also using your DVOM. Use the same hookups as before to measure the voltage of the coolant, but this time while cranking the engine, then with the engine running and lights and heater on. If stray current is grounding through the coolant, you'll get a voltage reading. More than 0.15 volts can corrode aluminum, and 0.3 volts can be harmful to cast iron. Check, clean and tighten the ground straps and/or battery ground connection to eliminate the problem.”


Evidently, the coolant should be slightly alkaline, with the desired pH level depending on the amount of aluminum in the system, compared with cast iron.

The same forum page says:

“Whether the coolant is acidic or alkaline makes a big difference. As long as it remains alkaline, corrosion is inhibited. But if it goes acidic, corrosion starts to eat away at the interior of the system. The corrosion-inhibiting additives in antifreeze are put there to keep the solution on the high side of the pH scale. The alkalinity of a typical antifreeze/water mixture will vary depending on the additives used and ratio of ingredients, but is usually somewhere between 8 and 11. The average for most antifreezes is around 10.5, but when diluted 50/50 with water and added to the coolin

random/checking_automobile_coolant.txt · Last modified: 2015/01/11 16:27 by ko4bb
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