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Until forty or so years ago, stray currents that eat radiators and water pumps etc were rarely encountered. This has changed. So-called electrolysis is now increasingly surfacing in post-1990 campervans and mini-motorhomes and also older campervans and motorhomes where owners have added electrical stuff up front, and/or where electrical connections are corroding or working loose.
But whilst it is being encountered (and its cause and prevention understood) many motor mechanics and auto electricians know little about it. This should hopefully change because the ‘Automobile, Electrical and Air Conditioning News’ commissioned me to explain how to locate and fix it. It will be published in the next issue of that trade journal.
Electrolysis is rarely visible, but easy to test for. Its cause is readily fixable by anyone who can use basic tools, but prior damage may cost thousands to fix. In the course of researching this article I found previously unsuspected and irreparable corrosion in our diesel Hilux’s water pump – (costing some $500 for a new pump).
The most common trigger is earth leads and metal bonding straps that have been poorly refitted, or even omitted, whilst replacing bits following front end accidents. It also happens when spot lights, electric radiator fans (particularly), and CB radios etc, are fitted or refitted.
Negative earth returns must be attached to metal that has a clear and secure electrical path to the battery negative terminal. Unless that path is 100% electrically sound, excess current will find its way back to battery haven by routes other than intended – and most commonly that is via the electrically-attractive cooling system and the metal around it.
The most probable damage is to solder joints in the radiator; corrosion of anything through which coolant flows; and rusting of iron components that in turn contaminate the coolant, and block the cooling and heating system.
As with our water pump, electrolysis may take a few years to cause major damage. Ours was traced to a windscreen washer pump that was replaced in 2005. (Essential note for Broome Toyota – it was not done by you!).
A poorly earthed starter motor may wreck an engine inside months.
Electrolysis issues were less common before 1975 or so in cars, and the early 1990s in campervans. Apart from spark plugs, lights, radio and a few ancillaries there wasn’t much to (un)earth. But then came the trend to front-wheel drive plus lots more electrics. There’s now more bits needing removing and replacing after front end shunts.
Compounding this are plastic (non-earthable) radiators cooled by high power electric fans. Lots of current and an alternative path through the coolant is not the best combination for all manner of metallic bits and pieces on the electrons’ trek home.
This is a less technical version of what I’ve told the auto sparkies.
All you need is a multimeter set to an approximately 0-10 volts range. Secure its negative probe securely to battery negative. Insert the positive into the radiator header tank’s coolant. That probe must contact the coolant but no metal.
With ignition off you may see an initial 0.5-0.7 volt. This is just a surface charge and should drop back after a couple of minutes. Wait until it settles.
The minimum conventionally acceptable reading is 0.3 volt for cast iron engines, and 0.1 volt for alloy engines (but see also below). If the voltage stays above that, something is causing it, for example a left-on CB radio connected directly across the battery.
To locate the cause, connect one end of a jumper lead to the suspect earthed lead – and the other to battery negative. If the meter reading drops you’ve located the area. If it doesn’t it is likely that whatever that lead is connected to is not earthed well – or at all.
Once that’s fixed, turn the ignition on and check again. If all is still well, check carefully whilst cranking the engine. It does not need to start. A high coolant voltage here is literally a potential engine eater.
Then run the engine for a moment or two to check the charging circuits. Next, and if the battery will withstand it (idle the engine otherwise) turn on everything electrical at the same time - especially spot lights and every other ancillary device on that vehicle. Check the meter for any increase.
If an excess reading is shown, locate the cause by switching things off progressively.
(It is not feasible to test for leakage one path at a time. There may be several minor problem paths, any one of which is insignificant but collectively form an excessive leakage path.)
Often the cause will be a cable ‘earthed’ via a loose self-tapping screw. Less likely (but it happens) is a frayed cable that has a wire whisker just touching a poorly earthed metal radiator.
In-line shower heat exchangers are not necessarily a problem, but certainly become one if they form part of a negative return path via a poorly earthed pump.
You may have to trace the entire earth path. The offending earth connection may be well made, but if that is to a piece of unbonded sheet metal, extend that lead to the chassis or a common negative power post as recommended and described in ‘Motorhome Electrics’.
You need two people to do this test – or you’ll need to extend the meter leads and find a way to hold that positive probe in the coolant, away from metal. And keep the leads out of the fan. Extending those leads by a few metres barely affects voltage measurement (but does for current).
The two most common causes are DIY’ed spotlights (especially with earth return via a radiator bracket). Second are electric radiator fans. And anything electrical that’s self fitted and close to the engine/transmission.
A quick and dirty check is to use a pH test strip - electrolysis sends the coolant acidic. This gives an indication, not a measurement. If acidic do the electrical test.
Extensive research indicates there’s no universal agreement on acceptable electrolysis voltage although most ‘authorities’ suggest an absolute maximum of 0.3 volt for cast iron and 0.1 volt for alloy, but I believe this is too high. Severe damage is known to be done (not just begin to occur) at 0.5 volt and 0.15 volt respectively. The present practice leaves insufficient margin for measuring error etc. I have respectfully suggested to the industry that 0.2 volt and 0.075 volt is safer yet still realistic.
Where vehicles have earth return there will always be some electrolysis simply because that earth return automatically provides an alternative parallel path. Electrically, there’s a resistive divider network.
With the gradual change to 42 volt electrics and electrical actuation increasingly replacing hydraulic, this situation can only worsen. My guess is that earth return will be replaced by individual positive and negative cabling. A few truck makers are doing this already (and I have strongly advised it for RV ‘house wiring’ in my books and other writings, since 1996).
Far from all corrosion is caused by electrolysis. There are many instances of severe corrosion where electrolysis voltage is fine. These are almost always caused by poor quality coolant, by diluting coolant, and particularly by those who just know that plain water is fine.
I met one (at a CMCA Rally) who swears by town water. He gets away with it only because his very old truck has (a) an engine that is basically a cast iron anvil with holes for the pistons and crankshaft. And (b) because it has next to no electrics – it’s a diesel with a few lights. Without intending offence, I do wish this member would accept his is an exceptional case and stop advising fellow members they are wasting money by not using plain water in their Sprinters etc. Top quality coolant has been absolutely essential for decades. Much town water now contains acid rain fallout. Coolant’s boiling point is also far higher.
I’d like to say there is more about electrolysis in my books, but right now this is it! An extended account however will be in the next issue of Motorhome Electrics – and there’s a lot there right now that it’s odds on you won’t know!
I need once again remind that all of my published writing is protected by the Commonwealth Copyright Act. And that includes in websites other than the CMCA’s.
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