electrolysis in aluminum radiators
 

So, what's the "straight dope" on electrolysis in aluminum radiators ?

Is this a test we should do on our Mercedes as preventativ maint. ?

:-) neil

taken from:
http://www.rondavisradiators.com/tech.htm

Electrolysis – Electrolysis is the systematic removal of the protective layer on the inside of the radiator tubes due to improper grounding. Electrical grounding problems can stem from poor installation of aftermarket accessories or incorrect vehicle collision damages.


Electrolysis facts

An electrical current passing through the coolant can cause system component failures, due to electrical ground problems and the generation of static electricity elsewhere in the vehicle. Electrical grounding problems can stem from poor installation of aftermarket accessories or incorrect vehicle collision damage repairs. This can destroy cooling system components regardless of the quality of cooling system maintenance. Depending on conditions it can be as quick as sixty days to ruin a radiator. The only way it can be stopped is to correct the electrical problem causing the current. Damage resulting from an electrical current can be pitted liners, oil coolers, radiators, extreme aluminum corrosion, and abnormal water pump and head gasket failure.

Testing for electrolysis in cooling systems

A voltmeter capable of reading both AC and DC currents is required to test cooling systems. The meter needs to read zero to the maximum voltage of the system being tested in tenths of a volt. The meter leads must be long enough to reach between the coolant and the groundside of the battery. An ohm function of a voltmeter is very helpful to pinpoint areas of resistance in as electrical system that will cause an electrical current to ground through the coolant rather than the engineered electrical circuit.
Procedure

1. Attach the proper meter lead to the groundside of the battery, negative-to-negative or positive-to-positive.

2.Install the second lead in the coolant touching the coolant only.

3. Read the DC and AC voltage with all systems off. If a block heater is present, also take a reading with the heater turned on. If an automatic battery charger is present, as a standby system, also take a reading with this system running.

4. Read the DC and AC voltage with the electrical starter engaged.

5. Read the DC and the AC voltage with the engine running and all systems turned on: lights, coolers, fans, heaters, air conditioning, cell phone, two-way radio, including the phone and radio on both standby and transmit.

6. The above procedure will test a complete system except for an electrical current, which can be generated by the rear end transmission. This is particularly true with air bag suspensions, rubber pad suspensions and rubber-mounted transmissions. Any current generated will travel up to the drive shaft to ground through the engine coolant. Grounding rear ends and transmissions is strongly recommended.

7. Voltage of zero to .3 is normal in a coolant of cast iron engine. Such an engine will be destroyed with time by .5 volts, and engine manufactures are reporting .15 volts will destroy an aluminum engine.

8. The current will be AC if the problem is due to static electricity.

9. If the coolant shows an electrical problem with all the equipment turned on; turn off one system at a time until you finally turn off the system that stops the electrical current. When the current stops, this will indicate the electrical system causing the problem.

10. Be partially careful of starters. They can cause as much damage to a cooling system as a direct connection to an arc welder. This is due to the amperage present.

11. Always change the coolant if a current is detected. The electrical current will destroy the protecting chemicals in a properly inhibited coolant.

It's not just the inexpensive aluminum radiator, its everything aluminum, including the expensive cylinder head.

I think that's a valid test. When I've measured my cars that all have coolant less than three years old they typically measure about 250 millivolts.

If you place two dissimilar metals in an electrolyte, even a weak electrolyte you have an electrolytic cell, which is essentially a battery - see any chemistry textbook.

If the "dry ends" of the metal are not connected there is no complete circuit and electrolytic corrosion should be minimal just like a battery doesn't loose charge fast unless the circuit is completed by connecting a load between the terminals. For this reason radiators should be electrically isolated from vehicle ground by rubber mounting. You should still see a few hundred ohms resistance between the radiator and ground due to the coolant path, but they should not be shorted.

In the case of aluminum heads and cast iron cylinder blocks, they are shorted together, so your best defense is frequent coolant changes with Zerex G-05 or MB antifreeze. Poor antifreeze maintenance can cause the head to erode at the block interface, which can cause head gasket failure.

Coolant is an electrolyte, but it has sophisticated additives to slow elecrolytic corrosion to a very low rate. These additives get depleted with time, and since electrolosis is a fact of life even when the engine isn't running (although the reaction rate is higher at operating temperature), Mercedes' recommended coolant change interval is strictly time based.

Duke

Duke,

have you read that some new models from Mercedes basically has a bag of silica gel to "replenish" the coolant ?

How does this work ?

Thanks,
:-) neil

I have never seen a car have a cooling system problem if the coolant was changed on schedual with the right stuff, and commen sense and preventive measures were used.

On the other hand, nearly every car I've taken care of has needed a new radiator in its old age, regardless of the fact that I changed coolant on schedule. Maybe I keep cars longer than everyone else?

Same here...I change antifreeze yearly and still have to do radiators every 6 years roughly. But the Aluminum/plastic radiators hold up the worst from my experience. I have good brass radiators that lasted 15+ years or more without issues.

It's a valid test, but that bozo made up a lot of crap. Why would anything "ground through the coolant" and bypass all the nice grounded metal in the driveline? :rolleyes: Just use a DC (voltage, not current, btw) meter with the negitive on bare engine metal and the positive in the coolant. If it reads .2 volts or more, change the coolant.

I've never seen one much less than about 200 MV, even with a known good cooling system and fresh antifreeze. Above 250-300 mv is possible trouble, but if you change coolant on a regular schedule this test is just a FYI, not a defintive test on coolant quality or cooling system corrosive activity.

Duke

Yes, and I think these models have a 10 or 12 year coolant change interval. I'm not sure how the bag of gel works, other than they replenish corrosion inhibitors that get consumed over time. I've not been able to get much information on how modern OAT and HOAT coolants protect against corrosion. Corrosion is a very complex subject. A lot of corrosion mechanisms are not well understood, and there aren't too many "corrosion control engineers" out there.

Some modern corrosion inhibitor formulations are patented, so a search of the patent documents could yield some answers on how they work.

Duke

Plastic ages, 10-15 years is about I expect out of a modern plastic/aluminum radiator. At the 10 year mark I start changing heater hoses, water pump, and t stat as preventive maintiance.


Nothing lasts forever.