Stray Currents
Our slant on Alloy radiator corrosion.
Stray current in cooling systems is a very controversial subject. There are several differing opinions about this subject. All metals by nature have a property that varies in value and when two differing metals are connected by an electrolyte (coolant) a current can be generated from one metal to the other. The combination of cast iron and aluminium can act as a simple battery. Stray current problems on the other hand are described as current used by independent electrical components finding another path back to the negative terminal of a battery rather than through the normal earth wire of the component. I am more convinced that in most cases of current measured in cooling systems with alloy radiator cores are self produced by the combination of two different metals and the glycol coolant/cocktail acting as an electrolyte.
Independent testing by UMR Engines has shown that a coolant charged system that has rather unacceptable levels of measured voltage( up to 0.46v) will be reduced to 0.26v by flushing and using only tap water as the coolant and as low as 0.02v with water and an added chemical that is described as “electrolysis arrestor.
Prior to aluminium radiator cores being used stray currents were not an issue.
The difference today is that we now have alloy cores, using glycol and corrosion inhibitors mixed with water as a coolant instead of copper cores with soluble oil as an additive in the radiator water. Vehicles always have had earth issues and have ran many and varied aftermarket accessories without radiator corrosion issues.
As to what is causing so called stray currents corrosion is not an exacting science.
There are no set procedures that are guaranteed to stop corrosion. Each vehicle has to be inspected and tested to try to determine the cause of the corrosion.
“Note: inform your customer that investigations and testing for stray currents is very time consuming and results are sometimes very changeable and require follow up investigations. Cost to the customer will vary and can only be based on actual time taken. Most customers think that the repairer is at fault but that is not the case. We call this the since you effect. Since you worked on our car the radiator leaks or the rear view mirror comes loose all the time
Here is a typical set of tests and tips:
(1) Using the positive probe of the multi meter placed in the coolant without touching the radiator core and the negative probe to the battery earth, check for current flow. Check the flow to be positive or negative.( +0.05V OR LOWER IS A SYSTEM PASS)
Start the engine and again carry out the same test. Now one at a time, turn on all the accessories such as Lights, fans, air con, brake lights, heaters, sound system, etc, if a change occurs then isolate the source and repair earth connections for that system. As a matter of importance check and clean all the normal earth straps and connections to the engine, transmission and computer looms. Check with the battery completely disconnected. CAUTION Prior to this test (save all radio codes and stored info or speak to the dealer as some late model BMW’s and other exotic vehicles have stored customer info that you could be forced by court to retrieve at a great cost to your business.)
(2) If the system shows positive voltage above 0.05v the system does not pass. If you are unable to find the cause, the cooling system has to be flushed out several times until all coolant is removed. Re-fill the system with clean water (preferred distilled or demineralised).
Check for stray currents and if within limits drop 50% of the water and add a glycol based coolant and recheck for stray currents.
Unfortunately just by adding the coolant a current can be generated that will stay as residual current in the system up until another 12 hours.
(3) After a 12 hour or more wait carry out a final test. If the stray current test result is below 0.05v that is now a system pass. Run vehicle and retest. Retest on a regular basis if vehicle has suffered previous corrosion failures.
(4) Some theorist believe the engine and cooling system have to be cleaned with a caustic cleaner to remove all the acidic deposits left on the internal parts of the engine water jackets by years of the glycol/cocktail use. This theory further strengthens the argument that the voltage is commonly self generated and produced by the two different metals and coolant with the alloy acting as the cathode resulting in the corrosion of the alloy parts.
(5) It is a proven theory that the highest rate of corrosion occurs at the point where the stray current leaves the structure as in underground buried pipes and railway systems etc. If a radiator core was to corrode due to the release of stray currents I would be very surprised to see the corrosion in the centre of an aluminium core that has no connection to earth. This also strengthens the theory that the radiator core is acting as a cathode as part of a self-generating battery.
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